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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2019	Mar. 01, 2020	Jun. 28, 2019
Document and Entity Information
Document Type	10-K
Document Period End Date	Dec. 31, 2019
Entity Registrant Name	Scholar Rock Holding Corp
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Public Float			$ 185.1
Entity Common Stock, Shares Outstanding		29,808,174
Entity Central Index Key	0001727196
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 36,308	$ 115,069
Marketable securities	121,140	60,576
Accounts receivable	25,000
Prepaid expenses and other current assets	2,719	2,296
Total current assets	185,167	177,941
Property and equipment, net	4,171	3,190
Operating lease right-of-use asset	4,447
Restricted cash	2,498	205
Other long-term assets	98
Total assets	196,381	181,336
Current liabilities:
Accounts payable	1,130	3,303
Accrued expenses	9,610	7,157
Deferred rent		16
Operating lease liability	1,135
Loan payable		424
Deferred revenue	20,923	20,209
Other current liabilities	16	14
Total current liabilities	32,814	31,123
Long-term portion of deferred rent		871
Long-term portion of operating lease liability	4,168
Other long-term liabilities	9	24
Long-term portion of deferred revenue	46,489	42,695
Total liabilities	83,480	74,713
Commitments and contingencies (Note 12)
Stockholders' equity:
Preferred stock, $0.001 par value; 10,000,000 shares authorized at December 31, 2019 and December 31, 2018; no shares issued and outstanding at December 31, 2019 and December 31, 2018
Common stock, $0.001 par value; 150,000,000 shares authorized and 29,792,922 shares issued and outstanding as of December 31, 2019; 150,000,000 shares authorized and 26,217,701 shares issued and outstanding as of December 31, 2018	30	26
Additional paid-in capital	270,682	213,453
Accumulated other comprehensive income (loss)	37	(8)
Accumulated deficit	(157,848)	(106,848)
Total stockholders' equity	112,901	106,623
Total liabilities and stockholders' equity	$ 196,381	$ 181,336

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENT OF FINANCIAL POSITION
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	150,000,000	150,000,000
Common stock, shares issued	29,792,922	26,217,701
Common stock, shares outstanding	29,792,922	26,217,701

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
CONSOLIDATED STATEMENT OF COMPREHENSIVE LOSS
Revenue	$ 20,492
Operating expenses:
Research and development	54,217	$ 36,310
General and administrative	20,817	14,382
Total operating expenses	75,034	50,692
Loss from operations	(54,542)	(50,692)
Other income (expense), net	3,542	1,366
Net loss	$ (51,000)	$ (49,326)
Net loss per share, basic and diluted (in dollars per share)	$ (1.85)	$ (3.15)
Weighted average common shares outstanding, basic and diluted (in shares)	27,537,939	15,655,293
Comprehensive loss:
Net loss	$ (51,000)	$ (49,326)
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities	45	(6)
Total other comprehensive income (loss)	45	(6)
Comprehensive loss	$ (50,955)	$ (49,332)

CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit	Total
Balance at beginning at Dec. 31, 2017	$ 4	$ 4,001	$ (2)	$ (57,525)	$ (53,522)
Balance at beginning (in shares) at Dec. 31, 2017	3,970,586
Increase (decrease) in Stockholders' Equity
Unrealized gain (loss) on marketable securities			(6)		(6)
Reclassification of warrant to stockholders' equity		93			93
Conversion of convertible preferred stock into common stock	$ 15	109,217			109,232
Conversion of convertible preferred stock into common stock (in shares)	15,109,950
Sale of common shares sold in IPO, net of offering costs	$ 6	77,833			77,839
Sale of common shares sold in IPO, net of offering costs (in shares)	6,164,000
Sale of common shares, net of issuance costs	$ 1	17,095			17,096
Sale of common shares (in shares)	980,392
Restricted shares forfeited during the period (in shares)	(8,125)
Exercise of stock options		6			6
Exercise of stock options (in shares)	898
Equity-based compensation expense		5,211			5,211
Cumulative effective adjustment for ASU 2018-07		(3)		3
Net Loss				(49,326)	(49,326)
Balance at end at Dec. 31, 2018	$ 26	213,453	(8)	(106,848)	106,623
Balance at end (in shares) at Dec. 31, 2018	26,217,701
Increase (decrease) in Stockholders' Equity
Unrealized gain (loss) on marketable securities			45		45
Sale of common shares, net of issuance costs	$ 4	48,344			48,348
Sale of common shares (in shares)	3,450,000
Restricted shares forfeited during the period (in shares)	(4,210)
Exercise of stock options		913			913
Exercise of stock options (in shares)	129,431
Equity-based compensation expense		7,972			7,972
Net Loss				(51,000)	(51,000)
Balance at end at Dec. 31, 2019	$ 30	$ 270,682	$ 37	$ (157,848)	$ 112,901
Balance at end (in shares) at Dec. 31, 2019	29,792,922

CONSOLIDATED STATEMENTS OF CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - Temporary Equity - 12 months ended Dec. 31, 2018 - USD ($) $ in Thousands	Convertible preferred stock	Total
Balance, beginning at Dec. 31, 2017	$ 109,232
Balance, beginning (in shares) at Dec. 31, 2017	43,135,911
Convertible preferred equity
Conversion of convertible preferred stock into common stock	$ (109,232)	$ 109,232
Conversion of convertible preferred stock into common stock (in shares)	(43,135,911)
Balance, end at Dec. 31, 2018	$ 0
Balance, end (in shares) at Dec. 31, 2018	0

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (51,000)	$ (49,326)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,303	807
Gain or loss on sale of property and equipment	(8)
Equity-based compensation	7,972	5,211
Amortization/accretion of investment securities	(1,390)	(345)
Non-cash operating lease expense	997
Deferred payroll tax credit	176	272
Change in operating assets and liabilities:
Accounts receivable	(25,000)
Prepaid expenses and other current assets	(739)	(1,276)
Other assets	(98)
Accounts payable	(1,342)	1,664
Accrued expenses	2,453	4,361
Deferred rent		191
Operating lease liabilities	(888)
Deferred revenue	4,508	62,904
Other liabilities	(59)	108
Net cash (used in) provided by operating activities	(63,115)	24,571
Cash flows from investing activities:
Purchase of property and equipment	(3,115)	(1,492)
Purchase of marketable securities	(235,417)	(75,239)
Proceeds from sale of property and equipment	8
Sales and maturities of marketable securities	176,288	16,500
Net cash used in investing activities	(62,236)	(60,231)
Cash flows from financing activities:
Principal payments on loan payable	(365)	(667)
Proceeds from sale of common stock, net of issuance costs	48,348	94,935
Proceeds from stock option exercises	913	6
Other	(13)	(6)
Net cash provided by financing activities	48,883	94,268
Net (decrease) increase in cash and cash equivalents and restricted cash	(76,468)	58,608
Cash and cash equivalents and restricted cash, beginning of period	115,274	56,666
Cash and cash equivalents and restricted cash, end of period	38,806	115,274
Supplemental disclosure of non-cash items:
Property and equipment purchases in accounts payable and accrued expenses		$ 439
Operating lease right-of-use asset obtained in exchange for operating lease obligation	$ 5,444

Nature of the Business and Basis of Presentation	12 Months Ended
Nature of the Business and Basis of Presentation	Dec. 31, 2019
Nature of the Business and Basis of Presentation
Nature of the Business and Basis of Presentation	1. Nature of the Business and Basis of Presentation Organization Scholar Rock Holding Corporation (the “Company”) is a biopharmaceutical company focused on the discovery and development of innovative medicines for the treatment of serious diseases in which signaling by protein growth factors plays a fundamental role. The Company’s novel understanding of the molecular mechanisms of growth factor activation enabled the development of a proprietary platform for the discovery and development of monoclonal antibodies that locally and selectively target these signaling proteins at the cellular level. The Company’s first product candidate, SRK-015, is a highly selective fully human, monoclonal antibody, with a unique mechanism of action that results in inhibition of the activation of the growth factor, myostatin, in skeletal muscle. SRK-015 is being developed as a potential first muscle-directed therapy for the treatment of spinal muscular atrophy (“SMA”). SRK-015 is being evaluated in the Company’s TOPAZ Phase 2 proof-of-concept trial for the treatment of patients with Type 2 and Type 3 SMA. The Company’s second product candidate, SRK-181, is being developed for the treatment of cancers that are resistant to checkpoint inhibitor (“CPI”) therapies, such as anti-PD-1 or anti-PD-L1 (collectively called anti-PD-(L)1) antibody therapies. SRK-181 is a potent and highly selective inhibitor of the activation of latent transforming growth factor beta-1 (“TGFβ1”). In the first quarter of 2020, the Company initiated a Phase 1 proof-of-concept clinical trial of SRK-181 in patients with locally advanced or metastatic solid tumors that exhibit primary resistance to anti-PD-(L)1 antibodies. Additionally, the Company continues to create a pipeline of novel product candidates with the potential to transform the lives of patients suffering from a wide range of serious diseases, including neuromuscular disorders, cancer, fibrosis and anemia. The Company was originally formed in May 2012. Its principal offices are in Cambridge, Massachusetts. Since its inception, the Company’s operations have focused on research and development of monoclonal antibodies that selectively inhibit activation of growth factors for therapeutic effect, as well as establishing the Company’s intellectual property portfolio and performing research and development activities. The Company has primarily financed its operations through various equity financings, including the initial public offering of its common stock (the “IPO”) in May 2018 and a secondary offering in June 2019 (Note 9), as well as research and development collaboration agreements. Revenue generation activities have been limited to two collaborations, both containing research services and the issuance of a license. The first agreement, executed in 2013, was with Janssen Biotech, Inc. (“Janssen”), a subsidiary of Johnson & Johnson. The second agreement (the “Gilead Collaboration Agreement”), executed in December 2018, was with Gilead Sciences, Inc. (“Gilead”). The Company began recognizing revenue on the Gilead Collaboration Agreement in 2019. No revenues have been recorded from the sale of any commercial product. The Company is subject to a number of risks similar to other life science companies, including, but not limited to, successful discovery and development of its drug candidates, raising additional capital, development by its competitors of new technological innovations, protection of proprietary technology and regulatory approval and market acceptance of the Company’s products. The Company anticipates that it will continue to incur significant operating losses for the next several years as it continues to develop its product candidates. The Company believes that its existing cash and cash equivalents, and marketable securities at December 31, 2019 will be sufficient to allow the Company to fund its current operations through at least a period of one year after the date the financial statements are issued. Basis of Presentation The consolidated financial statements include the accounts of Scholar Rock Holding Corporation and its wholly owned subsidiaries. All intercompany balances have been eliminated in consolidation. These consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the U.S. (“GAAP”). Any reference in these notes to applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Update (“ASU”) of the Financial Accounting Standards Board (“FASB”).

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2019

Summary of Significant Accounting Policies

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Use of Estimates

The preparation of financial statements in accordance with GAAP requires management to make estimates and judgments that may affect the reported amounts of assets and liabilities and related disclosures of contingent assets and liabilities at the date of the financial statements and the related reporting of revenues and expenses during the reporting period. Significant estimates of accounting reflected in these consolidated financial statements include, but are not limited to, estimates related to revenue recognition, research and development, accrued expenses, the valuation of equity-based compensation, including common stock, restricted common stock and stock options, and income taxes. Actual results could differ from those estimates.

Prior to the IPO, the Company utilized significant estimates and assumptions in determining the fair value of its equity-based compensation, including common stock, restricted common stock and stock options. The Company utilized various valuation methodologies in accordance with the framework of the 2013 American Institute of Certified Public Accountants Technical Practice Aid, Valuation of Privately-Held Company Equity Securities Issued as Compensation, to estimate the fair value of its equity awards. Each valuation methodology included estimates and assumptions that required the Company’s judgment. These estimates and assumptions included a number of objective and subjective factors, including external market conditions, guideline public company information, the prices at which the Company sold convertible preferred units and convertible preferred stock, the superior rights and preferences of securities senior to the Company’s common units and common stock at the time and the likelihood of achieving a liquidity event such as an initial public offering or sale. Significant changes to the assumptions used in the valuations could have resulted in different fair values of common stock, restricted common stock and stock options at each valuation date, as applicable.

Concentration of Credit Risk and Off-Balance Sheet Risk

The Company has no off-balance sheet risk, such as foreign exchange contracts, option contracts or other foreign-hedging arrangements. The Company follows an investment policy approved by the Board of Directors. Its primary objectives are the preservation of capital and maintenance of liquidity. The Company invests only in fixed income instruments denominated and payable in U.S. dollars including obligations of the U.S. government and its agencies and money market funds registered according to SEC Rule 2a‑7 of the Investment Company Act of 1940. All securities must have a readily ascertainable market value, must be readily marketable and be U.S. dollar denominated.

Cash and Cash Equivalents and Restricted Cash

The Company considers highly liquid investments with a maturity of three months or less when purchased to be cash equivalents. Cash equivalents are stated at cost, which approximates market value. At December 31, 2019 and 2018, cash equivalents include money market funds that invest primarily in U.S. government-backed securities and treasuries.

Restricted cash consists of letters of credit in the amount of $2.5 million related to its leased facilities. The following table reconciles cash and cash equivalents and restricted cash per the balance sheet to the statement of cash flows:


	As of December 31,
	2019		2018
Cash and cash equivalents	$	36,308	$	115,069
Restricted cash		2,498		205
	$	38,806	$	115,274

Property and Equipment

Property and equipment are recorded at cost. Expenditures for major renewals or betterments that extend the useful lives of property and equipment are capitalized; expenditures for maintenance and repairs are charged to expense as incurred. Depreciation is calculated on a straight-line basis over the estimated useful lives of the related asset. Property and equipment are depreciated as follows:


		Estimated Useful Life
		(in Years)
Laboratory equipment		3 – 5
Computer equipment & software		3
Furniture & fixtures		5
Machinery & equipment		3 – 5
Leasehold improvements		Shorter of the useful life or remaining lease term

Impairment of Long-Lived Assets

Long-lived assets consist of property and equipment and right-of-use assets. Long-lived assets to be held and used are tested for recoverability whenever events or changes in business circumstances indicate that the carrying amount of the assets may not be fully recoverable. Factors that the Company considers in deciding when to perform an impairment review include significant underperformance of the business in relation to expectations, significant negative industry or economic trends and significant changes or planned changes in the use of the assets. If an impairment review is performed to evaluate a long-lived asset group for recoverability, the Company compares forecasts of undiscounted cash flows expected to result from the use and eventual disposition of the long-lived asset group to its carrying value. An impairment loss would be recognized when estimated undiscounted future cash flows expected to result from the use of an asset group are less than its carrying amount. The impairment loss would be based on the excess of the carrying value of the impaired asset group over its fair value, determined based on discounted cash flows. The Company did not record any impairment losses on long-lived assets during the years ended December 31, 2019 or 2018.

Leases

Effective January 1, 2019, the Company adopted ASC Topic 842, Leases (“ASC 842”), using the modified retrospective approach and utilizing the effective date as its date of initial application, for which prior periods are presented in accordance with the previous guidance in ASC Topic 840, Leases. The Company elected the package of practical expedients permitted under the transition guidance.

At the inception of an arrangement, the Company determines whether the arrangement is or contains a lease based on the unique facts and circumstances present. Leases with a term greater than one year are recognized on the balance sheet as right-of-use assets, lease liabilities and, if applicable, long-term lease liabilities. Operating lease liabilities and their corresponding right-of-use assets are recorded based on the present value of lease payments over the expected remaining lease term. However, certain adjustments to the right-of-use asset may be required for items such as incentives received. The interest rate implicit in lease contracts is typically not readily determinable. As a result, the Company utilizes its incremental borrowing rates, which are the rates incurred to borrow on a collateralized basis over a similar term an amount equal to the lease payments in a similar economic environment.

In accordance with the guidance in ASC 842, components of a lease should be split into three categories: lease components (e.g. land, building, etc.), non-lease components (e.g. common area maintenance, consumables, etc.), and non-components (e.g. property taxes, insurance, etc.) Then the fixed and in-substance fixed contract consideration (including any related to non-components) must be allocated based on the respective relative fair values to the lease components and non-lease components. For operating leases, lease expense relating to fixed payments is recognized on a straight-line basis over the term and lease expense relating to variable payments is expensed as incurred.

Fair Value Measurements

ASC Topic 820, Fair Value Measurement ("ASC 820"), establishes a fair value hierarchy for instruments measured at fair value that distinguishes between assumptions based on market data (observable inputs) and the Company’s own assumptions (unobservable inputs). Observable inputs are inputs that market participants would use in pricing the asset or liability based on market data obtained from sources independent of the Company. Unobservable inputs are inputs that reflect the Company’s assumptions about the inputs that market participants would use in pricing the asset or liability and are developed based on the best information available in the circumstances. ASC 820 identifies fair value as the exchange price, or exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As a basis for considering market participant assumptions in fair value measurements, ASC 820 establishes a three-tier fair value hierarchy that distinguishes between the following:

Level 1 — Quoted market prices in active markets for identical assets or liabilities.

Level 2 — Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves.

Level 3 — Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use.

To the extent the valuation is based on models or inputs that are less observable or unobservable in the market, the determination of fair values requires more judgment. Accordingly, the degree of judgment exercised by the Company in determining fair value is greatest for instruments categorized as Level 3. A financial instrument’s level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement.

Segment Information

Operating segments are defined as components of an entity about which separate discrete information is available for evaluation by the chief operating decision maker, or decision-making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment operating exclusively in the U.S.

Revenue Recognition

The Company accounts for revenue using the provisions of ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”). Under ASC 606, an entity recognizes revenue when its customer obtains control of promised goods or services, in an amount that reflects the consideration which the entity expects to receive in exchange for those goods or services. To determine the appropriate amount of revenue to be recognized for arrangements determined to be within the scope of ASC 606, the Company performs the following five steps: (i) identification of the contract(s) with the customer, (ii) identification of the promised goods or services in the contract and determination of whether the promised goods or services are performance obligations, (iii) measurement of the transaction price, (iv) allocation of the transaction price to the performance obligations, and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the entity will collect consideration it is entitled to in exchange for the goods or services it transfers to the customer. At contract inception, once the contract is determined to be within the scope of ASC 606, the Company assesses the goods or services promised within each contract and determines those that are performance obligations, and assesses whether each promised good or service is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied.

The Company accounts for a contract with a customer that is within the scope of ASC 606 when all of the following criteria are met: (i) the arrangement has been approved by the parties and the parties are committed to perform their respective obligations, (ii) each party’s rights regarding the goods or services to be transferred can be identified, (iii) the payment terms for the goods or services to be transferred can be identified, (iv) the arrangement has commercial substance and (v) collection of substantially all of the consideration to which the Company will be entitled in exchange for the goods or services that will be transferred to the customer is probable.

The Company first evaluates license and/or collaboration arrangements to determine whether the arrangement (or part of the arrangement) represents a collaborative arrangement pursuant to ASC Topic 808, Collaborative Arrangements, based on the risks and rewards and activities of the parties pursuant to the contractual arrangement. The Company accounts for collaborative arrangements (or elements within the contract that are deemed part of a collaborative arrangement), which represent a collaborative relationship and not a customer relationship, outside of the scope of ASC 606. The Company’s existing collaborations represent revenue arrangements.

For the arrangements or arrangement components that are subject to revenue accounting guidance, in determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of its agreements, the Company performs the following steps: (i) identification of the promised goods or services in the contract; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including the constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when (or as) the Company satisfies each performance obligation. As part of the accounting for these arrangements, the Company must use significant judgment to determine: a) the number of performance obligations based on the determination under step (ii) above and whether those performance obligations are distinct from other performance obligations in the contract; b) the transaction price under step (iii) above; and c) the standalone selling price for each performance obligation identified in the contract for the allocation of transaction price in step (iv) above. The Company uses judgment to determine whether milestones or other variable consideration, except for royalties, should be included in the transaction price as described further below. The transaction price is allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. In determining the stand-alone selling price of a license to the Company’s proprietary technology or a material right provided by a customer option, the Company considers market conditions as well as entity-specific factors, including those factors contemplated in negotiating the agreements as well as internally developed estimates that include assumptions related to the market opportunity, estimated development costs, probability of success and the time needed to commercialize a product candidate pursuant to the license. In validating its estimated stand-alone selling prices, the Company evaluates whether changes in the key assumptions used to determine its estimated stand-alone selling prices will have a significant effect on the allocation of arrangement consideration between performance obligations.

The Company estimates the transaction price based on the amount of consideration the Company expects to be received for transferring the promised goods or services in the contract. The consideration may include both fixed consideration and variable consideration. At the inception of each arrangement that includes variable consideration, the Company evaluates the amount of the potential payments and the likelihood that the payments will be received. The Company utilizes either the most likely amount method or expected value method to estimate the transaction price based on which method better predicts the amount of consideration expected to be received. If it is probable that a significant revenue reversal would not occur, the variable consideration is included in the transaction price.

Performance obligations are promised goods or services in a contract to transfer a distinct good or service to the customer. Promised goods or services are considered distinct when: (i) the customer can benefit from the good or service on its own or together with other readily available resources and (ii) the promised good or service is separately identifiable from other promises in the contract. In assessing whether promised goods or services are distinct, the Company considers factors such as the stage of development of the underlying intellectual property, the capabilities of the customer to develop the intellectual property on their own and whether the required expertise is readily available.

The Company allocates the transaction price based on the estimated standalone selling price. The Company must develop assumptions that require judgment to determine the standalone selling price for each performance obligation identified in the contract. The Company utilizes key assumptions to determine the standalone selling price, which may include other comparable transactions, pricing considered in negotiating the transaction and the estimated costs. Estimating costs for research and development programs is subjective as the Company estimates the costs anticipated to successfully complete the research performance obligations. As the research is novel, efforts to be successful may be significantly different than the estimated costs at the beginning of the contract. Certain variable consideration is allocated specifically to one or more performance obligations in a contract when the terms of the variable consideration relate to the satisfaction of the performance obligation and the resulting amounts allocated to each performance obligation are consistent with the amounts the Company would expect to receive for each performance obligation.

For performance obligations which consist of licenses and other promises, the Company utilizes judgment to assess the nature of the combined performance obligation in order to determine whether the combined performance obligation is satisfied over time or at a point in time. The Company determines the appropriate method of measuring progress of combined performance obligations satisfied over time for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The estimated remaining costs is highly subjective, as the research is novel, therefore efforts to be successful may be significantly different than the estimated costs made at the balance sheet date. If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company will recognize revenue from non-refundable, up-front fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. The Company receives payments from customers based on billing schedules established in each contract. Up-front payments and fees are recorded as deferred revenue upon receipt or when due until the Company performs its obligations under these arrangements. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current portion of deferred revenue in the accompanying consolidated balance sheets. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue, net of current portion. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. Amounts recognized as revenue, but not yet received or invoiced are generally recognized as contract assets.

Exclusive Licenses – If the license granted in the arrangement is determined to be distinct from the other promises or performance obligations identified in the arrangement, which generally include research and development services, the Company recognizes revenue from non-refundable, upfront fees allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. In assessing whether a license is distinct from the other promises, the Company considers relevant facts and circumstances of each arrangement, including the research and development capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can benefit from the license for its intended purpose without the receipt of the remaining promise, whether the value of the license is dependent on the unsatisfied promise, whether there are other vendors that could provide the remaining promise, and whether it is separately identifiable from the remaining promise. For licenses that are combined with other promises, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. The measure of progress, and thereby periods over which revenue should be recognized, are subject to estimates by management and may change over the course of the arrangement.

Research and Development Services – The promises under the Company’s collaboration and license agreements generally include research and development services to be performed by the Company on behalf of the collaboration partner. For performance obligations that include research and development services, the Company generally recognizes revenue allocated to such performance obligations based on an appropriate measure of progress. The Company utilizes judgment to determine the appropriate method of measuring progress for purposes of recognizing revenue, which is generally an input measure, such as costs incurred. The Company evaluates the measure of progress each reporting period as described under Exclusive Licenses above. Reimbursements from the partner that are the result of a collaborative relationship with the partner, instead of a customer relationship, such as co-development activities, are generally recorded as a reduction to research and development expense.

Customer Options – The Company’s arrangements may provide a collaborator with the right to certain optional purchases, such as the right to license a target either at the inception of the arrangement or within a pre-defined option period. Under these agreements, fees may be due to the Company (i) at the inception of the arrangement as an upfront fee or payment or (ii) upon the exercise of an option to acquire a license. If an arrangement is determined to contain customer options that allow the customer to acquire additional goods or services, the goods and services underlying the customer options are not considered to be performance obligations at the outset of the arrangement, as they are contingent upon option exercise. The Company evaluates the customer options for material rights, or options to acquire additional goods or services for free or at a discount. If the customer options are determined to represent a material right, the material right is recognized as a separate performance obligation at the inception of the arrangement. The Company allocates the transaction price to material rights based on the relative stand-alone selling price, which is determined based on the identified discount, and the probability that the customer will exercise the option. Amounts allocated to a material right are not recognized as revenue until, at the earliest, the option is exercised or expires.

Milestone Payments – At the inception of each arrangement that includes milestone payments based on certain events, the Company evaluates whether the milestones are considered probable of being achieved and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable of being achieved until those approvals are received. The Company evaluates factors such as the scientific, clinical, regulatory, commercial, and other risks that must be overcome to achieve the particular milestone in making this assessment. There is considerable judgment involved in determining whether it is probable that a significant revenue reversal would not occur. At the end of each subsequent reporting period, the Company reevaluates the probability of achievement of all milestones subject to constraint and, if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. If a milestone or other variable consideration relates specifically to the Company’s efforts to satisfy a single performance obligation or to a specific outcome from satisfying the performance obligation, the Company generally allocates the milestone amount entirely to that performance obligation once it is probable that a significant revenue reversal would not occur.

Royalties – For arrangements that include sales-based royalties, including milestone payments based on a level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its licensing arrangements.

For a complete discussion of accounting for collaboration revenues, see Note 14, Agreements.

Research and Development Expenses and Accruals

Research and development expenses are expensed as incurred and consist of costs incurred in performing research and development activities, including compensation related expenses for research and development personnel, preclinical and clinical activities including cost of supply, overhead expenses including facilities expenses, materials and supplies, amounts paid to consultants and outside service providers, and depreciation of equipment. Upfront license payments related to acquired technologies which have not yet reached technological feasibility and have no alternative future use are also included in research and development expense.

The Company has entered into various research and development service arrangements under which vendors perform various services. The Company records accrued expenses for estimated costs incurred under the arrangements. When evaluating the adequacy of the accrued expenses, the Company analyzed the progress of the studies, trials or other services performed, including invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued expense balances at the end of each reporting period.

Equity-Based Compensation

The Company accounts for equity awards, including common stock, restricted common stock, common stock options, granted to employees as equity award compensation in accordance with ASC Topic 718, Compensation — Stock Compensation ("ASC 718"). ASC 718 requires all stock-based payments to employees, which includes grants of employee equity awards, to be recognized as expense in the statements of operations based on their grant date fair values.

Prior to becoming a public company, the Company estimated the fair value of common stock using an appropriate valuation methodology, based on the guideline public company (“GPC”) method or the precedent transaction method which "backsolves" to a preferred price. The use of these valuation approaches requires management to make assumptions with respect to the expected volatility of its common stock, time until a liquidity event and risk-free interest rates. The fair value of each restricted common stock award is based on the fair value of the Company’s common stock less any purchase price, if applicable. The fair value of each stock option award is estimated using the Black-Scholes option-pricing model, which uses as inputs the fair value of the Company’s common stock and certain subjective assumptions, including the expected stock price volatility, the expected term of the award, the risk-free rate, and expected dividends. Expected volatility is calculated based on reported volatility data for a representative group of publicly traded companies for which historical information was available. The historical volatility is generally calculated based on a period of time commensurate with the expected term assumptions. The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant commensurate with the expected term assumption. The Company uses the simplified method, under which the expected term is presumed to be the midpoint between the vesting date and the end of the contractual term. The Company utilizes this method due to lack of historical exercise data and the plain nature of its stock-based awards. The expected dividend yield is assumed to be zero as the Company has never paid dividends and has no current plans to pay any dividends on common stock.

Compensation expense related to equity awards to employees that are subject to graded vesting is recognized on a straight-line basis, based on the grant date fair value, over the requisite service period of the award, which is generally the vesting term. For awards subject to performance conditions, the Company recognizes equity award compensation expense using an accelerated recognition method over the remaining service period when management determines that achievement of the milestone is probable. Management evaluates when the achievement of a performance-based milestone is probable based on the relative satisfaction of the performance conditions as of the reporting date.

The Company adopted ASU No. 2018-07, Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting (“ASU 2018-07”) in the fourth quarter of 2018. The standard expands the scope of ASC 718 to include all share-based payment arrangements related to the acquisition of goods and services from both non-employees and employees. Prior to the adoption of ASU 2018-07, for equity awards granted to non-employees, the Company accounted for the related equity award compensation in accordance with the provisions of ASC 718 and ASC Topic 505, Equity, and recognized equity award compensation expense over the related service period of the non-employee award. Equity awards issued to non-employees were recorded at their fair values, using the then-current fair value of the common stock and updated assumption inputs in the Black-Scholes option-pricing model, as applicable, and were periodically revalued as the equity instruments vested. After the adoption of ASU 2018-07, equity-classified share-based payment awards issued to non-employees are measured at grant date fair value similarly to those of employees and are no longer revalued as the equity instruments vest. The new standard allows entities to use the expected term to measure non-employee options or elect to use the contractual term as the expected term, on an award-by-award basis.

The Company classifies equity-based compensation expense in its consolidated statements of operations in the same manner in which the award recipient’s salary and related costs are classified or in which the award recipient’s service payments are classified.

The Company accounts for forfeitures when they occur.

Convertible Preferred Stock

The Company records all convertible preferred shares at their respective fair values on the dates of issuance less issuance costs. The Company classifies its convertible preferred shares outside of stockholders’ equity when the redemption of such shares is outside the Company’s control. The Company does not adjust the carrying values of the convertible preferred stock to the liquidation preferences of such units or shares until such time as a deemed liquidation event is probable of occurring.

Comprehensive Loss

Comprehensive loss is the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Comprehensive loss includes net loss and the change in accumulated other comprehensive income (loss) for the period. Accumulated other comprehensive loss consisted entirely of unrealized gains and losses on available-for-sale marketable securities during the period ending December 31, 2019 and 2018.

Net Loss per Share

The Company applies the two-class method to compute basic and diluted net loss per share because it has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income (losses) available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to share in the earnings as if all income (losses) for the period had been distributed. During periods of loss, there is no allocation required under the two-class method since the participating securities do not have a contractual obligation to fund the losses of the Company.

The Company calculates basic net loss per share by dividing net loss by the weighted average number of common shares outstanding, excluding restricted common stock. The Company calculates diluted net loss per share by dividing net loss by the weighted average number of common shares outstanding, as applicable, after giving consideration to the dilutive effect of convertible preferred stock, restricted common stock, warrants and stock options that are outstanding during the period.

Income Taxes

Income taxes for Scholar Rock Holding Corporation and Scholar Rock, Inc. are recorded in accordance with ASC Topic 740, Income Taxes ("ASC 740"), which provides for deferred taxes using an asset and liability approach. Under this method, deferred income tax assets and liabilities are recognized based on future income tax consequences attributable to differences between the financial statement carrying amount of existing assets and liabilities, and their respective income tax basis. Deferred income tax assets and liabilities are measured using enacted income tax rates expected to apply to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect of changes in income tax rates on deferred income tax assets and liabilities is recognized as income or expense in the period that a valuation allowance for any income tax benefits of which future realization is not more likely than not.

The Company provides reserves for potential payments of tax to various tax authorities related to uncertain tax positions, as necessary. The tax benefits recorded are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is "more likely than not" to be realized following resolution of any uncertainty related to the tax benefit, assuming that the matter in question will be raised by the tax authorities.

The Company is open to examination by the Internal Revenue Service for the tax years ended December 31, 2013 to December 31, 2019. Since the Company is in a U.S. loss carryforward position, carryforward tax attributes generated in prior years may still be adjusted upon future examination if they have or will be used in a future period. The Company is currently not under examination by the Internal Revenue Service or any other jurisdictions for any tax years. The Company has not recorded any interest or penalties on any unrecognized tax benefits since its inception.

Marketable Securities

The Company classifies its marketable securities as available-for-sale. Marketable securities with a remaining maturity date greater than one year are classified as non-current. Marketable securities are maintained by an investment manager and consist of U.S. treasury securities. Marketable securities are carried at fair value with the unrealized gains and losses included in accumulated other comprehensive loss as a component of stockholders’ equity until realized. Any premium or discount arising at purchase is amortized and/or accreted to interest income and/or expense over the life of the underlying marketable security.

Although available to be sold to meet operating needs or otherwise, securities are generally held through maturity. The cost of securities sold is determined on a specific identification basis, and realized gains and losses are included in other income (expense) within the statement of operations and comprehensive loss. During the years ended December 31, 2019 and 2018, there was an immaterial amount of realized gains on sales of marketable securities and no marketable securities were adjusted for other than temporary declines in fair value.

The Company evaluates its marketable securities with unrealized losses for other-than-temporary impairment. When assessing marketable securities for other-than-temporary declines in value, the Company considers such factors as, among other things, how significant the decline in value is as a percentage of the original cost, how long the market value of the investment has been less than its original cost, the Company’s ability and intent to retain the investment for a period of time sufficient to allow for any anticipated recovery in fair value and market conditions in general. If any adjustment to fair value reflects a decline in the value of the investment that the Company considers to be "other than temporary," the Company would reduce the investment to fair value through a charge to the statement of operations and comprehensive loss. No such adjustments were necessary during the periods presented.

Deferred Offering Costs

The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ equity as a reduction of additional paid-in capital generated as a result of the offering. Should the planned equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the consolidated statement of operations and comprehensive loss.

Recently Adopted Accounting Pronouncements

In February 2016, the FASB issued ASU 2016-02, Leases, (“ASU 2016-02”), which superseded the lease accounting requirements in ASC 840, Leases and created a new Topic 842, Leases.

In adopting the new standard, the Company elected to utilize the available package of practical expedients permitted under the transition guidance within the new standard, which removed the requirement to reassess previous accounting conclusions around whether arrangements are or contain leases, the classification of leases, and the treatment of initial direct costs. The adoption of this standard resulted in the recognition of operating lease liabilities and right-of-use assets of $6.2 million and $5.4 million, respectively, as of January 1, 2019. There was no cumulative transition adjustment to retained earnings upon adoption of the standard and there was no material effect on the Company’s statements of operations or statement of cash flows as the difference relates to previously recorded deferred rent which was eliminated upon adoption of this standard.

Recently Issued Accounting Pronouncements

In August 2018, the FASB issued ASU 2018-15, Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract. The new standard will align the requirements for capitalizing implementation costs for hosting arrangements (services) with costs for internal-use software (assets). As a result, certain implementation costs incurred in hosting arrangements will be deferred and amortized. The new standard will be effective for the Company on January 1, 2020. The Company does not anticipate a material impact to its net financial position or disclosures as a result of the adoption of ASU 2018-15.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The standard requires that a financial asset or a group of financial assets measured at amortized cost basis to be presented at the net amount expected to be collected. Under current GAAP, a company only considered past events and current conditions in measuring an incurred loss. Under ASU 2016-13, the information that a company must consider is broadened in developing an expected credit loss estimate for assets measured either collectively or individually. The use of forecasted information incorporates more timely information in the estimate of expected credit loss. The guidance is applied using a modified retrospective, or prospective approach, depending on a specific amendment. In November 2019, the FASB deferred the effective date for smaller reporting companies to fiscal years beginning after December 15, 2022. The Company does not anticipate a material impact to its net financial position or disclosures as a result of the adoption of ASU 2016-13.

Fair Value of Financial Assets and Liabilities

12 Months Ended

Dec. 31, 2019

Fair Value of Financial Assets and Liabilities

Fair Value of Financial Assets and Liabilities

3. Fair Value of Financial Assets and Liabilities

The following tables summarize the assets and liabilities measured at fair value on a recurring basis at December 31, 2019 and 2018 (in thousands):


	Fair Value Measurements at December 31, 2019
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds, included in cash and cash equivalents	$	34,896	$	34,896	$	—	$	—
Marketable securities:
U.S. Treasury obligations		121,140		121,140		—		—
Total assets	$	156,036	$	156,036	$	—	$	—


	Fair Value Measurements at December 31, 2018
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds, included in cash and cash equivalents	$	114,593	$	114,593	$	—	$	—
Marketable securities:
U.S. Treasury obligations		60,576		60,576		—		—
Total assets	$	175,169	$	175,169	$	—	$	—

Cash and cash equivalents and marketable securities include investments in money market funds and U.S. government securities that are valued using quoted market prices. Accordingly, money market funds and government funds are categorized as Level 1 as of December 31, 2019 and 2018. There were no transfers of assets between fair value measurement levels during the years ended December 31, 2019 and 2018.

The carrying amounts reflected in the balance sheets for accounts receivable, prepaid expenses and other current assets, accounts payable, and accrued expenses approximate their fair values at December 31, 2019 and 2018, due to their short-term nature.

Upon the completion of the IPO, the Company’s outstanding warrant to purchase preferred stock converted into a warrant to purchase common stock and the Company reclassified the fair value of the warrant to additional paid-in capital. As of December 31, 2019, the warrant is currently exercisable for 7,614 shares of the Company’s common stock at an exercise price of $3.94 per share.

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Marketable Securities

12 Months Ended

Dec. 31, 2019

Marketable Securities

Marketable Securities

4. Marketable Securities

The following table summarizes the Company’s investments as of December 31, 2019 (in thousands):


			Gross
	Amortized		Unrealized				Estimated
	Cost		Gains		Losses		Fair Value
Marketable securities available-for-sale:
U.S. Treasury obligations	$	121,103	$	39	$	(2)	$	121,140
Total available-for-sale securities	$	121,103	$	39	$	(2)	$	121,140

The following table summarizes the Company’s investments as of December 31, 2018 (in thousands):


			Gross
	Amortized		Unrealized				Estimated
	Cost		Gains		Losses		Fair Value
Marketable securities available-for-sale:
U.S. Treasury obligations	$	60,584	$	—	$	(8)	$	60,576
Total available-for-sale securities	$	60,584	$	—	$	(8)	$	60,576

The aggregate fair value of marketable securities with unrealized losses was $19.6 million and $60.6 million at December 31, 2019 and 2018, respectively. At December 31, 2019 and 2018, 3 investments and 16 investments, respectively, were in an unrealized loss position. All such investments have been in an unrealized loss position for less than a year and these losses are considered temporary. The Company has the ability and intent to hold these investments until a recovery of their amortized cost, which may be until maturity.

Property and Equipment, Net

12 Months Ended

Dec. 31, 2019

Property and Equipment, Net

Property and Equipment, Net

5. Property and Equipment, Net

At December 31, 2019 and 2018, property and equipment consists of the following (in thousands):


	December 31,		December 31,
	2019		2018
Laboratory equipment	$	5,432	$	3,585
Leasehold improvements		1,580		1,578
Computer equipment & software		423		—
Furniture & fixtures		219		219
Machinery & equipment		75		75
Construction in progress		—		89
		7,729		5,546
Less: Accumulated depreciation and amortization		(3,558)		(2,356)
	$	4,171	$	3,190

Depreciation and amortization expense was $1.3 million and $0.8 million for the years ended December 31, 2019 and 2018, respectively.

Accrued Expenses

12 Months Ended

Dec. 31, 2019

Accrued Expenses

Accrued Expenses

6. Accrued Expenses

At December 31, 2019 and 2018, accrued expenses consist of the following (in thousands):


	As of
	December 31,		December 31,
	2019		2018
Accrued external research and development expense	$	4,088	$	3,284
Accrued payroll and related expenses		4,380		2,826
Accrued professional and consulting expense		929		890
Accrued other		213		157
	$	9,610	$	7,157

Convertible Preferred Stock	12 Months Ended
Convertible Preferred Stock	Dec. 31, 2019
Convertible Preferred Stock.
Convertible Preferred Stock	7. Convertible Preferred Stock The Series A‑1, A‑2, A‑3, A‑4, B, and C Convertible Preferred Stock are collectively referred to as Convertible Preferred Stock. In conjunction with the IPO, all Convertible Preferred Stock was converted to common stock.

Preferred Stock	12 Months Ended
Preferred Stock	Dec. 31, 2019
Common Stock and Preferred Stock
Common Stock and Preferred Stock	8. Preferred Stock The Board of Directors or any authorized committee thereof is expressly authorized, to the fullest extent permitted by law, to provide by resolution or resolutions for, out of the unissued shares of Preferred Stock, the issuance of the shares of Preferred Stock in one or more series of such stock, and by filing a certificate of designations pursuant to applicable law of the State of Delaware, to establish or change from time to time the number of shares of each such series, and to fix the designations, powers, including voting powers, full or limited, or no voting powers, preferences and the relative, participating, optional or other special rights of the shares of each series and any qualifications, limitations and restrictions thereof. In connection with the consummation of the IPO, on May 29, 2018 the Company filed an amended and restated certificate of incorporation which authorized for issuance 10,000,000 shares of Preferred Stock, par value $0.001. As of December 31, 2019, no shares of the Preferred Stock were issued or outstanding.

Common Stock

12 Months Ended

Dec. 31, 2019

Common Stock.

Common Stock

9. Common Stock

In June and July 2019, the Company sold 3,450,000 shares of its common stock, including the exercise of the overallotment option, through an underwritten public offering at a price of $15.00 per share. The offering was made pursuant to the Company’s effective shelf registration statement on Form S‑3. The Company received aggregate net proceeds, after underwriting discounts and commissions and other offering expenses, of approximately $48.3 million.

During the second quarter of 2018, the Company completed its IPO, in which the Company sold 6,164,000 shares of common stock, including all additional shares available to cover overallotments, at a price of $14.00 per share. The Company received aggregate net proceeds of approximately $77.8 million, after deducting underwriting discounts and commissions and other offering expenses payable by the Company. Upon the closing of the IPO, all outstanding shares of convertible preferred stock converted into 15,109,950 shares of common stock and the Company’s outstanding warrant to purchase preferred stock converted into a warrant to purchase 7,614 shares of common stock.

In connection with the consummation of the IPO, on May 29, 2018 the Company filed an amended and restated certificate of incorporation, which increased the number of shares of common stock authorized for issuance thereunder by 90,000,000 shares to 150,000,000 shares.

The voting, dividend and liquidation rights of the holders of common stock are subject to and qualified by the rights, powers and preferences of the holders of Preferred Stock. The common stock has the following characteristics:

Voting

The holders of shares of common stock are entitled to one vote for each share of common stock held at any meeting of stockholders and at the time of any written action in lieu of a meeting.

Dividends

The holders of shares of common stock are entitled to receive dividends, if and when declared by the Company’s Board of Directors. No dividends have been declared or paid by the company to the holders of common stock since the issuance of the common stock.

Liquidation

The holders of common stock are entitled to share ratably in the Company’s net assets available for distribution to its stockholders in the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company or upon the occurrence of a deemed liquidation event.

Shares Reserved For Future Issuance

As of December 31, 2019, the Company had reserved common shares as follows:


		As of
		December 31,
		2019
Common shares reserved for exercise of a warrant		7,614
Common shares reserved for future issuance under the 2018 ESPP		497,920
Common shares reserved for exercise of outstanding stock options under the 2017 and 2018 Plans		2,401,382
Common shares reserved for future issuance under the 2018 Plan		2,684,464
		5,591,380

Equity-Based Compensation

12 Months Ended

Dec. 31, 2019

Equity-Based Compensation

Equity-Based Compensation

10. Equity-Based Compensation

Equity Plans

As of December 31, 2019, the Company has three active equity plans, the 2018 Stock Option and Incentive Plan (the “2018 Plan”), the 2017 Stock Option and Incentive Plan (the “2017 Plan”), and the 2018 Employee Stock Purchase Plan (the “2018 ESPP”).

2018 Stock Option and Incentive Plan

The 2018 Plan was adopted by the Company’s Board of Directors on May 2, 2018, and approved by the Company’s stockholders on May 11, 2018. The 2018 Plan has replaced the 2017 Plan as no additional awards will be granted under that plan following the consummation of the IPO. The Company initially reserved 3,139,274 shares of common stock for the issuance of awards under the 2018 Plan (the “Initial Limit”), which included 352,204 unused shares reserved for issuance under the 2017 Plan that became available under the 2018 Plan upon the completion of the IPO.

The 2018 Plan provides for the grant of equity-based incentive awards, including incentive stock options, non‑qualified stock options, restricted stock awards, unrestricted stock awards and restricted stock units to the Company’s officers, employees, directors and other key persons (including consultants). Stock options granted under the 2018 Plan to employees generally vest over four years. The shares of common stock underlying any awards that are forfeited, cancelled, repurchased or are otherwise terminated by the Company under the 2018 Plan will be added back to the shares of common stock available for issuance under the 2018 Plan.

The 2018 Plan provides that the number of shares reserved and available for issuance under the plan will automatically increase each January 1, beginning on January 1, 2019, by 4% of the outstanding number of shares of common stock on the immediately preceding December 31 or such lesser number of shares as determined by the Board of Directors or compensation committee (the “Annual Increase”). These limits are subject to adjustment in the event of a stock split, stock dividend or other change in the Company’s capitalization.

2017 Stock Option and Incentive Plan

The 2017 Plan provides for the grant of incentive stock options, non‑qualified stock options, restricted stock awards, unrestricted stock awards and restricted stock units. Stock options granted under the 2017 Plan to employees generally vest over four years. The number of shares initially reserved for issuance under the 2017 Plan was 3,455,330 shares of common stock. The shares of common stock underlying any awards that are forfeited, cancelled, repurchased or are otherwise terminated by the Company under the 2017 Plan will be added back to the shares of common stock available for issuance under the 2018 Plan.

2018 Employee Stock Purchase Plan

On May 2, 2018, the Board of Directors adopted the 2018 ESPP, and it was approved by the stockholders on May 11, 2018. The 2018 ESPP initially reserved and authorized the issuance of 235,743 shares of common stock to participating employees. The ESPP provides that the number of shares reserved and available for issuance will automatically increase each January 1, beginning on January 1, 2019, by the lesser of (i) 353,614 shares of common stock, (ii) 1% of the outstanding number of shares of the Company’s common stock on the immediately preceding December 31 or (iii) such lesser number of shares as determined by the 2018 ESPP administrator. The number of shares reserved under the 2018 ESPP is subject to adjustment in the event of a stock split, stock dividend or other change in the Company’s capitalization. As of December 31, 2019, no shares have been issued under the 2018 ESPP.

Total Equity‑Based Compensation Expense

The Company recorded equity‑based compensation expense related to all equity‑based awards for employees and non‑employees, which was allocated as follows in the consolidated statements of operations and comprehensive loss (in thousands):


	Year Ended
	December 31,
	2019		2018
Research and development expense	$	2,425	$	1,661
General and administrative expense		5,547		3,550
	$	7,972	$	5,211

Equity-based compensation during the year ended December 31, 2019 includes $0.6 million and $0.1 million related to the acceleration and modification, respectively, of certain equity awards. Equity-based compensation during the year ended December 31, 2018 includes $1.2 million related to the modification of certain other equity awards.

Restricted Stock

The following table summarizes restricted common stock activity as of December 31, 2019:


		Weighted
		Average Fair
		Value per Share
	Number of Shares	at Issuance
Restricted common stock as of December 31, 2018	664,174	$	5.77
Granted	—	$	—
Vested	(357,604)	$	5.77
Forfeited	(4,210)	$	5.77
Restricted common stock as of December 31, 2019	302,360	$	5.77

As of December 31, 2019, the Company had unrecognized equity-based compensation expense of $1.3 million related to restricted stock issued to employees and directors, which is expected to be recognized over a period of 1.2 years.

Stock Options

The following table summarizes the Company’s stock option activity as of December 31, 2019:


				Weighted
		Weighted		Average
	Number of	Average		Remaining	Aggregate
	Shares	Exercise Price		Contractual Term	Intrinsic Value
				(in years)	(in thousands)
Outstanding as of December 31, 2018	1,627,947	$	10.86	9.26	$	19,831
Granted	1,034,825	$	15.07
Exercised	(129,431)	$	7.06
Cancelled	(131,959)	$	15.46
Outstanding as of December 31, 2019	2,401,382	$	12.63	8.36	$	6,523
Options exercisable as of December 31, 2019	787,537	$	11.17	7.40	$	2,902

Using the Black-Scholes option pricing model, the weighted average fair value of options granted to employees and directors during the year ended December 31, 2019 was $10.53.

The following assumptions were used in determining the fair value of options granted in the year ended December 31, 2019:


Risk-free interest rate	2.31	%
Expected dividend yield	0.0	%
Expected term (years to liquidity)	6.20
Expected volatility	79.50	%

As of December 31, 2019, the Company has unrecognized equity-based compensation expense related to its employee stock options of $13.8 million which the Company expects to recognize over the remaining weighted-average vesting period of 2.6 years.

Income Taxes

12 Months Ended

Dec. 31, 2019

Income Taxes

Income Taxes

11. Income Taxes

The Company has not recorded a current or deferred tax provision for the years ended December 31, 2019 and 2018.

The effective income tax rate differed from the amount computed by applying the federal statutory rate to the Company’s loss before income taxes as follows:


	For Year Ended
	December 31,
	2019		2018
Tax effected at statutory rate	21.0	%	21.0	%
State taxes	7.2		6.6
Stock compensation	(1.7)		(1.7)
Non deductible expenses	(0.4)		(0.1)
Federal research and development credits	7.8		5.9
Change in valuation allowance	(33.9)		(31.7)
	—	%	—	%

Deferred tax assets (liabilities) consist of the following at December 31, 2019 and 2018 (in thousands):


	As of
	December 31,
	2019		2018
Deferred tax assets:
Reserve and accruals	$	1,704	$	1,031
Net operating loss carryforwards		26,932		25,380
Deferred rent		—		242
Operating lease liability		1,448		—
Deferred revenue		13,173		3,525
Tax credits		9,569		4,976
Stock based compensation		1,049		314
Total gross deferred tax assets		53,875		35,468
Valuation allowance		(52,260)		(34,970)
Total deferred tax assets		1,615		498
Total deferred tax liabilities:
Operating lease right-of-use asset		(1,214)		—
Fixed and intangible assets		(401)		(498)
Total deferred tax liabilities		(1,615)		(498)
Total net deferred tax assets	$	—	$	—

Total Net Deferred Tax Assets

Deferred tax assets are reduced by a valuation allowance if, based on the weight of available positive and negative evidence, it is more likely than not that some portion or all of the deferred tax assets will not be realized. Accordingly, a full valuation allowance has been established against the net deferred tax assets as of December 31, 2019 and 2018. The valuation allowance for deferred tax assets increased by $17.3 million and $19.2 million in 2019 and 2018, respectively. This increase mainly relates to the establishment of a valuation allowance against the Company’s net domestic deferred tax assets in connection with net operating losses generated in each year and the recording of additional net operating losses and credit carryforwards, partially offset by a revaluation of the federal deferred tax assets in 2018 based on the tax law change. As of December 31, 2019, the Company had approximately $98.1 million and $100.1 million of Federal and State operating loss carryforwards respectively, which begin to expire in 2032. The Company also had federal net operating loss carryforwards of $47.6 million that do not expire. These loss carryforwards are available to reduce future taxable income, if any. These loss carryforwards are subject to review and possible adjustment by the appropriate taxing authorities. As of December 31, 2019, the Company also had federal and state credit carryovers of $8.0 million and $2.0 million, respectively. The amount of loss and credit carryforwards that may be utilized in any future period may be limited based upon changes in the ownership of the Company’s ultimate parent. Additionally, the deductibility of federal net operating losses generated after December 31, 2017 is limited to 80% of the Company’s taxable income in any future taxable year.

The Company follows the provisions of ASC 740-10, “Accounting for Uncertainty in Income Taxes,” which specifies how tax benefits for uncertain tax positions are to be recognized, measured, and recorded in financial statements; requires certain disclosures of uncertain tax matters; specifies how reserves for uncertain tax positions should be classified on the balance sheet; and provides transition and interim period guidance, among other provisions. As of December 31, 2019 and 2018, the Company has not recorded any amounts for uncertain tax positions. The Company’s policy is to recognize interest and penalties accrued on any uncertain tax positions as a component of income tax expense, if any, in its statements of income.

Commitments and Contingencies

12 Months Ended

Dec. 31, 2019

Commitments and Contingencies

Commitments and Contingencies

12. Commitments and Contingencies

Operating Leases

620 Memorial Facility Lease

In March 2015, the Company entered into a 5‑year facility lease for its corporate headquarters (the “lease”) at 620 Memorial Drive in Cambridge, Massachusetts. The lease was amended in February 2018, to add an additional space (the “expansion space”) at the current location and to extend the lease term (the “amended lease”). The amended lease expires in September 2023. Rent for the facility lease, including the expansion space, increases from $1.4 million a year to $1.7 million a year over the term of the lease. Variable lease payments include the Company’s allocated share of costs incurred and expenditures made by the landlord in the operation and management of the building. The Company has the option to extend the term of the amended lease for one additional term of 5 years commencing after the amended lease expires.

Other information related to the Company’s lease is as follows (in thousands, except lease term and discount rate):


	For Year Ended
	December 31,
	2019
Lease Cost:
Operating lease cost	$	1,375
Variable lease cost		674
Total lease cost	$	2,049


	For Year Ended
	December 31,
	2019
Other information:
Operating cash flows used for operating leases	$	1,266
Weighted average remaining lease term		3.75 years
Weighted average incremental borrowing rate		6.47	%

The following is a maturity analysis of the annual undiscounted cash flows reconciled to the carrying value of the operating lease liabilities as of December 31, 2019 (in thousands):


Year Ending December 31,
2020	$	1,446
2021		1,619
2022		1,668
2023		1,279
Total lease payments		6,012
Less imputed interest		(709)
Total operating lease liabilities	$	5,303

The Company recorded approximately $1.4 million and $1.0 million in rent expense for the years ended December 31, 2019 and 2018, respectively.

301 Binney Facility Lease

In November 2019, the Company entered into a facility lease at 301 Binney Street in Cambridge, Massachusetts to be used as its new corporate headquarters. The Company is involved in the construction and design of the space and anticipates that it will incur construction costs, subject to an allowance for tenant improvements of up to $14.1 million. No construction costs have been incurred as of December 31, 2019. The expiration date of the lease is in August 2025 and the Company has the option to extend the term by two years. The base rent is $6.9 million per year, subject to an increase of 3.5%, and the Company is subject to a free-rent period through mid-August 2020. Variable lease payments include the Company’s allocated share of costs incurred and expenditures made by the landlord in the operation and management of the building. In connection with the facility lease, the Company has secured a letter of credit for $2.3 million which renews automatically each year. The lease commencement date, for accounting purposes, was not reached as of December 31, 2019 and therefore the lease is not included in the Company’s operating lease right-of-use asset or operating lease liabilities as of December 31, 2019.

Legal Proceedings

The Company, from time to time, may be party to litigation arising in the ordinary course of its business. The Company was not subject to any material legal proceedings during the years ended December 31, 2019 and 2018.

Loan Payable	12 Months Ended
Loan Payable	Dec. 31, 2019
Loan Payable
Loan Payable	13. Loan Payable In August 2015, the Company entered into a Loan and Security Agreement with Silicon Valley Bank (“SVB”), which provided the Company an equipment line of credit of up to $2.0 million to finance the purchase of eligible equipment, which the Company borrowed the full $2.0 million against the line of credit. The loan balance at December 31, 2018 was $0.4 million. The Company made the final payments on the loan in June 2019. For the years ended December 31, 2019 and 2018, the Company recorded total interest expense for this loan of $27,000 and $0.1 million, respectively.

Agreements	12 Months Ended
Agreements	Dec. 31, 2019
Agreements
Agreements	14. Agreements Collaboration with Gilead Agreement Summary On December 19, 2018 (the “Effective Date”), the Company entered into a Master Collaboration Agreement (the “Gilead Collaboration Agreement”) with Gilead to discover and develop specific inhibitors of TGFβ activation focused on the treatment of fibrotic diseases. Under the collaboration, Gilead has exclusive options to license worldwide rights to product candidates that emerge from three of the Company’s TGFβ programs (each a “Gilead Program”). Pursuant to the Gilead Collaboration Agreement, the Company is responsible for antibody discovery and preclinical research through product candidate nomination, after which, upon exercising the option for a Gilead Program, Gilead will be responsible for the program’s preclinical and clinical development and commercialization. Such option may be exercised by Gilead at any time from the Effective Date through a date that is 90 days following the expiration of the Research Collaboration Term (as defined below) for a given Gilead Program, or until termination of the Gilead Program, whichever is earlier (the “Option Exercise Period”). The Company received a non-refundable upfront payment of $50 million under the Gilead Collaboration Agreement. If Gilead exercises its option to exclusively license a Gilead Program, the Company may earn a total potential aggregate option exercise fee, development, regulatory and commercial milestone payments with respect to each Gilead Program of $475 million, or a total of $1,425 million across all three Gilead Programs. Additionally, in partial consideration of the rights granted to Gilead pursuant to the License Agreement, Gilead shall pay to the Company certain tiered royalties at a rate ranging from the high single-digits to the low double-digits (depending on the amount of net sales) on each Licensed Product in a given calendar year, on a country-by-country basis. In December 2019, the Company achieved a $25 million preclinical milestone for the successful demonstration of efficacy in preclinical in vivo proof-of-concept studies. None of the payments under the Gilead Collaboration Agreement are refundable. Simultaneously with the entry into the Gilead Collaboration Agreement, the Company entered into a Share Purchase Agreement with Gilead (the “Gilead Equity Agreement”). Pursuant to the terms of the Gilead Equity Agreement, Gilead purchased 980,392 shares of common stock of the Company (the “Shares”) at a purchase price of $30.60 per share, for an aggregate purchase price of $30 million. The Company did not incur any material costs in connection with the issuance of the Shares. The Company and Gilead have established a joint steering committee (the “JSC”). The JSC, among other powers and responsibilities, reviews, oversees and has decision-making responsibilities for certain strategic activities performed under the Gilead Programs, including reviewing and amending the research plans, reviewing any development candidate nominations, selecting a development candidate, and overseeing the strategic direction of the Gilead Programs. The Company conducts its activities for each Gilead Program under the Gilead Collaboration Agreement, on a program-by-program basis, during the period beginning on the Effective Date and ending on the earliest to occur of (a) the date that the JSC first approves a selected development candidate for such program, (b) the third anniversary of the Effective Date, or (c) the effective date of termination of the Gilead Collaboration Agreement (the “Research Collaboration Term”). During the Research Collaboration Term, for each Gilead Program, the Company will notify Gilead, through the JSC, of up to two Gilead Program antibodies (in the case that Gilead rejects one, in accordance with the terms of the Gilead Collaboration Agreement) that satisfy the development criteria for such program (the “Development Candidate Nomination”). The Gilead Collaboration Agreement remains in effect, unless otherwise earlier terminated in accordance with the terms of the Gilead Collaboration Agreement, on a program-by-program basis, until Gilead exercises its option with respect to a given Gilead Program or until expiration of the applicable Option Exercise Period, whichever is earlier (the “Term”). Unless earlier terminated, the Term shall expire in its entirety upon the expiration of the last to expire Option Exercise Period under the Gilead Collaboration Agreement. Gilead may terminate the Gilead Collaboration Agreement in its entirety or on a program-by-program basis in its sole discretion upon prior written notice to the Company pursuant to the terms of the agreement. The Gilead Collaboration Agreement may also be terminated on a program-by-program basis by either party in the event of an uncured material breach of the Gilead Collaboration Agreement by the other party. Prior to Gilead’s exercise of an option, the Company has the lead responsibility for drug discovery and pre-clinical development of all Gilead Programs through to Development Candidate Nomination. Within a certain period of time after receiving a data package for a Development Candidate Nomination, Gilead may exercise its option to enter into a Form of License Agreement for exclusive rights to develop, manufacture and commercialize the licensed antibodies and licensed products of such Gilead Program. Accounting Treatment The Company assessed this arrangement in accordance with ASC 606 and concluded that the contract counterparty, Gilead, is a customer. The Company identified the following material promises under the arrangement: (1) the non-exclusive, royalty-free research and development license; (2) the research and development services for the Gilead Programs; and (3) the options to license each of the three Gilead Programs to develop, manufacture and commercialize licensed candidates and resulting products, which were determined to be material rights for each Gilead Program. The research and development services for each of the three Gilead Programs were determined to not be distinct from the research and development license and have been combined into a single performance obligation for each Gilead Program. Additionally, the option and associated material right for each Gilead Program represent separate performance obligations. The promises under the Gilead Collaboration Agreement relate primarily to the research and development required by the Company for each of the Gilead Programs nominated by Gilead. The Company does not have significant responsibilities subsequent to Gilead’s exercise of each option. At the commencement of the arrangement, two units of accounting were identified: the issuance of 980,392 of the Company’s common shares and the joint research activities during the three-year research collaboration term. The Company determined the total transaction price to be $80 million, consisting of $17.1 million attributed to the equity sold to Gilead and $62.9 million attributed to the joint research activities. In determining the fair value of the common stock at closing, the Company considered the closing price of the common stock at the time of the transaction and included a lack of marketability discount because the shares were subject to certain restrictions. Of the $30 million equity investment, $12.9 million was determined to be a premium and therefore was included as part of the transaction price to be allocated over the performance obligations. At the commencement of the arrangement, the $25 million milestone for the successful demonstration of efficacy in preclinical in vivo proof-of-concept studies was not included in the transaction price. The Company will reevaluate the transaction price at the end of each reporting period and as uncertain events are resolved or other changes in circumstances occur, and, if necessary, will adjust its estimate of the transaction price. The $62.9 million attributed to the joint research activities was allocated to the performance obligations based on their standalone selling prices (the “SSP”) when the Gilead Collaboration Agreement was executed. The Company made certain estimates when determining the SSP. For the research licenses and related research and development services, the estimated SSP is primarily based on the nature of the services to be performed and estimates of the associated effort and costs of the services. The Company developed the estimated SSP for the material rights based on the intrinsic value of the license upon exercise of the underlying option, industry standards for product development and estimates for the likelihood of option exercise. The consideration related to the underlying options will not be included in the transaction price until the options are exercised. Additionally, the subsequent potential development, regulatory and commercial milestones are excluded from the transaction price, until after Gilead exercises its respective options. Revenue associated with the research and development and license performance obligations relating to the Gilead Programs is recognized as revenue as the research and development services are provided using an input method, according to the costs incurred on each Gilead Program and the costs expected to be incurred in the future to satisfy the performance obligation. The transfer of control occurs over time. In management’s judgment, this input method is the best measure of progress towards satisfying the performance obligation. The amounts allocated to the three material rights will be recognized when Gilead exercises each respective option and delivers the underlying license and transfer of know-how, or immediately as each option expires unexercised. The amounts received that have not yet been recognized as revenue are recorded in deferred revenue on the Company’s consolidated balance sheet. None of the performance obligations have been fully satisfied as of December 31, 2019. A $25 million preclinical milestone was achieved in December 2019 for the successful demonstration of efficacy in preclinical in vivo proof-of-concept studies. As a result, the associated $25 million was included in the consideration transferred and proportionally allocated to the performance obligations, as it was probable that a future material reversal will not occur. In 2019, the Company recognized $20.5 million in revenue under the Gilead Collaboration Agreement, of which $14.7 million was included in the deferred revenue balance at the beginning of the period. The aggregate amount of the transaction price allocated to the Company’s unsatisfied performance obligations and recorded in deferred revenue at December 31, 2019 is $67.4 million. The Company will recognize the deferred revenue related to the research and development services based on a cost input method, over the remaining research term for each respective Gilead Program, which is a maximum of 2 years as of December 2019; each research term is dependent on the timing of Gilead either exercising its options for the Gilead Programs or terminating further development on the Gilead Programs prior to the expiration date of the research term.

Net Loss per Share

12 Months Ended

Dec. 31, 2019

Net Loss per Share

Net Loss per Share

15. Net Loss per Share

The Company calculates basic net loss per share by dividing net loss by the weighted average number of common shares outstanding, excluding restricted common stock. The Company has generated a net loss in all periods presented, so the basic and diluted net loss per share are the same, as the inclusion of the potentially dilutive securities would be anti-dilutive.

Basic and diluted net loss per share is calculated as follows (in thousands, except share and per share data):


	Year Ended		Year Ended
	December 31, 2019		December 31, 2018
Net loss	$	(51,000)	$	(49,326)
Weighted average common shares outstanding, basic and diluted		27,537,939		15,655,293
Net loss per share, basic and diluted	$	(1.85)	$	(3.15)

The following table sets forth the outstanding common stock equivalents, presented based on amounts outstanding at each period end, that have been excluded from the calculation of diluted net loss per share for the periods indicated because their inclusion would have been anti‑dilutive:


	Year Ended December 31,
	2019	2018
Restricted common stock	302,360	664,174
Warrant	7,614	7,614
Stock options	2,401,382	1,627,947
	2,711,356	2,299,735

Retirement Plan	12 Months Ended
Retirement Plan	Dec. 31, 2019
Retirement Plan
Retirement Plan	16. Retirement Plan The Company sponsors a 401(K) retirement plan, in which substantially all employees are eligible to participate upon employment. Participants may contribute a percentage of their annual compensation to this plan, subject to statutory limitations. The Company did not provide any contributions to this plan during the years ended December 31, 2019 and 2018.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2019

Summary of Significant Accounting Policies

Use of Estimates

Concentration of Credit Risk and Off-Balance Sheet Risk

Cash and Cash Equivalents and Restricted Cash


	As of December 31,
	2019		2018
Cash and cash equivalents	$	36,308	$	115,069
Restricted cash		2,498		205
	$	38,806	$	115,274

Property and Equipment


		Estimated Useful Life
		(in Years)
Laboratory equipment		3 – 5
Computer equipment & software		3
Furniture & fixtures		5
Machinery & equipment		3 – 5
Leasehold improvements		Shorter of the useful life or remaining lease term

Impairment of Long-Lived Assets

Leases

Fair Value Measurements

Level 1 — Quoted market prices in active markets for identical assets or liabilities.

Level 2 — Inputs other than Level 1 inputs that are either directly or indirectly observable, such as quoted market prices, interest rates and yield curves.

Level 3 — Unobservable inputs developed using estimates of assumptions developed by the Company, which reflect those that a market participant would use.

Segment Information

Revenue Recognition

For a complete discussion of accounting for collaboration revenues, see Note 14, Agreements.

Research and Development Expenses and Accruals

Equity-Based Compensation

The Company accounts for forfeitures when they occur.

Convertible Preferred Stock

Comprehensive Loss

Net Loss per Share

Income Taxes

Marketable Securities

Deferred Offering Costs

Recently Adopted and Issued Accounting Pronouncements

Recently Adopted Accounting Pronouncements

In February 2016, the FASB issued ASU 2016-02, Leases, (“ASU 2016-02”), which superseded the lease accounting requirements in ASC 840, Leases and created a new Topic 842, Leases.

Recently Issued Accounting Pronouncements

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2019

Summary of Significant Accounting Policies

Schedule of reconciles of cash and cash equivalents and restricted cash


	As of December 31,
	2019		2018
Cash and cash equivalents	$	36,308	$	115,069
Restricted cash		2,498		205
	$	38,806	$	115,274

Schedule of useful life of property, plant and equipment


		Estimated Useful Life
		(in Years)
Laboratory equipment		3 – 5
Computer equipment & software		3
Furniture & fixtures		5
Machinery & equipment		3 – 5
Leasehold improvements		Shorter of the useful life or remaining lease term

Fair Value of Financial Assets and Liabilities (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value of Financial Assets and Liabilities

Schedule of summary of the assets and liabilities measured at fair value on a recurring basis

The following tables summarize the assets and liabilities measured at fair value on a recurring basis at December 31, 2019 and 2018 (in thousands):


	Fair Value Measurements at December 31, 2019
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds, included in cash and cash equivalents	$	34,896	$	34,896	$	—	$	—
Marketable securities:
U.S. Treasury obligations		121,140		121,140		—		—
Total assets	$	156,036	$	156,036	$	—	$	—


	Fair Value Measurements at December 31, 2018
	Total		Level 1		Level 2		Level 3
Assets:
Money market funds, included in cash and cash equivalents	$	114,593	$	114,593	$	—	$	—
Marketable securities:
U.S. Treasury obligations		60,576		60,576		—		—
Total assets	$	175,169	$	175,169	$	—	$	—

Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2019

Marketable Securities

Summary of investments

The following table summarizes the Company’s investments as of December 31, 2019 (in thousands):


			Gross
	Amortized		Unrealized				Estimated
	Cost		Gains		Losses		Fair Value
Marketable securities available-for-sale:
U.S. Treasury obligations	$	121,103	$	39	$	(2)	$	121,140
Total available-for-sale securities	$	121,103	$	39	$	(2)	$	121,140

The following table summarizes the Company’s investments as of December 31, 2018 (in thousands):


			Gross
	Amortized		Unrealized				Estimated
	Cost		Gains		Losses		Fair Value
Marketable securities available-for-sale:
U.S. Treasury obligations	$	60,584	$	—	$	(8)	$	60,576
Total available-for-sale securities	$	60,584	$	—	$	(8)	$	60,576

Property and Equipment, Net (Tables)

12 Months Ended

Dec. 31, 2019

Property and Equipment, Net

Summary of property and equipment

At December 31, 2019 and 2018, property and equipment consists of the following (in thousands):


	December 31,		December 31,
	2019		2018
Laboratory equipment	$	5,432	$	3,585
Leasehold improvements		1,580		1,578
Computer equipment & software		423		—
Furniture & fixtures		219		219
Machinery & equipment		75		75
Construction in progress		—		89
		7,729		5,546
Less: Accumulated depreciation and amortization		(3,558)		(2,356)
	$	4,171	$	3,190

Accrued Expenses (Tables)

12 Months Ended

Dec. 31, 2019

Accrued Expenses

Summary of accrued expenses

At December 31, 2019 and 2018, accrued expenses consist of the following (in thousands):


	As of
	December 31,		December 31,
	2019		2018
Accrued external research and development expense	$	4,088	$	3,284
Accrued payroll and related expenses		4,380		2,826
Accrued professional and consulting expense		929		890
Accrued other		213		157
	$	9,610	$	7,157

Common Stock (Tables)

12 Months Ended

Dec. 31, 2019

Common Stock.

Schedule of reserved common stock


		As of
		December 31,
		2019
Common shares reserved for exercise of a warrant		7,614
Common shares reserved for future issuance under the 2018 ESPP		497,920
Common shares reserved for exercise of outstanding stock options under the 2017 and 2018 Plans		2,401,382
Common shares reserved for future issuance under the 2018 Plan		2,684,464
		5,591,380

Equity-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Equity-Based Compensation

Summary of allocation of equity-based compensation


	Year Ended
	December 31,
	2019		2018
Research and development expense	$	2,425	$	1,661
General and administrative expense		5,547		3,550
	$	7,972	$	5,211

Summary of restricted common stock activity


		Weighted
		Average Fair
		Value per Share
	Number of Shares	at Issuance
Restricted common stock as of December 31, 2018	664,174	$	5.77
Granted	—	$	—
Vested	(357,604)	$	5.77
Forfeited	(4,210)	$	5.77
Restricted common stock as of December 31, 2019	302,360	$	5.77

Summary of stock option activity


				Weighted
		Weighted		Average
	Number of	Average		Remaining	Aggregate
	Shares	Exercise Price		Contractual Term	Intrinsic Value
				(in years)	(in thousands)
Outstanding as of December 31, 2018	1,627,947	$	10.86	9.26	$	19,831
Granted	1,034,825	$	15.07
Exercised	(129,431)	$	7.06
Cancelled	(131,959)	$	15.46
Outstanding as of December 31, 2019	2,401,382	$	12.63	8.36	$	6,523
Options exercisable as of December 31, 2019	787,537	$	11.17	7.40	$	2,902

Schedule of fair value assumptions


Risk-free interest rate	2.31	%
Expected dividend yield	0.0	%
Expected term (years to liquidity)	6.20
Expected volatility	79.50	%

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Taxes

Schedule of reconciliation of effective income tax rate differed from the amount computed by applying the federal statutory rate


	For Year Ended
	December 31,
	2019		2018
Tax effected at statutory rate	21.0	%	21.0	%
State taxes	7.2		6.6
Stock compensation	(1.7)		(1.7)
Non deductible expenses	(0.4)		(0.1)
Federal research and development credits	7.8		5.9
Change in valuation allowance	(33.9)		(31.7)
	—	%	—	%

Summary of deferred tax assets (liabilities)

Deferred tax assets (liabilities) consist of the following at December 31, 2019 and 2018 (in thousands):


	As of
	December 31,
	2019		2018
Deferred tax assets:
Reserve and accruals	$	1,704	$	1,031
Net operating loss carryforwards		26,932		25,380
Deferred rent		—		242
Operating lease liability		1,448		—
Deferred revenue		13,173		3,525
Tax credits		9,569		4,976
Stock based compensation		1,049		314
Total gross deferred tax assets		53,875		35,468
Valuation allowance		(52,260)		(34,970)
Total deferred tax assets		1,615		498
Total deferred tax liabilities:
Operating lease right-of-use asset		(1,214)		—
Fixed and intangible assets		(401)		(498)
Total deferred tax liabilities		(1,615)		(498)
Total net deferred tax assets	$	—	$	—

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2019

Commitments and Contingencies

Summary of lease costs

Other information related to the Company’s lease is as follows (in thousands, except lease term and discount rate):


	For Year Ended
	December 31,
	2019
Lease Cost:
Operating lease cost	$	1,375
Variable lease cost		674
Total lease cost	$	2,049


	For Year Ended
	December 31,
	2019
Other information:
Operating cash flows used for operating leases	$	1,266
Weighted average remaining lease term		3.75 years
Weighted average incremental borrowing rate		6.47	%

Summary of minimum lease payments

The following is a maturity analysis of the annual undiscounted cash flows reconciled to the carrying value of the operating lease liabilities as of December 31, 2019 (in thousands):


Year Ending December 31,
2020	$	1,446
2021		1,619
2022		1,668
2023		1,279
Total lease payments		6,012
Less imputed interest		(709)
Total operating lease liabilities	$	5,303

Net Loss per Share (Tables)

12 Months Ended

Dec. 31, 2019

Net Loss per Share

Schedule of basic and diluted net loss per share

Basic and diluted net loss per share is calculated as follows (in thousands, except share and per share data):


	Year Ended		Year Ended
	December 31, 2019		December 31, 2018
Net loss	$	(51,000)	$	(49,326)
Weighted average common shares outstanding, basic and diluted		27,537,939		15,655,293
Net loss per share, basic and diluted	$	(1.85)	$	(3.15)

Summary of anti-dilutive securities


	Year Ended December 31,
	2019	2018
Restricted common stock	302,360	664,174
Warrant	7,614	7,614
Stock options	2,401,382	1,627,947
	2,711,356	2,299,735

Nature of the Business and Basis of Presentation (Details)	12 Months Ended
	Dec. 31, 2019 item
Nature of the Business and Basis of Presentation
Number of collaborations	2

Summary of Significant Accounting Policies - Concentration of Credit Risk and Off-Balance Sheet Risk (Details) $ in Billions	Dec. 31, 2019 USD ($)
Summary of Significant Accounting Policies
Off-balance sheet risk	$ 0

Summary of Significant Accounting Policies - Cash and Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash and cash equivalents and restricted cash
Letter of credit	$ 2,500
Cash and cash equivalents	36,308	$ 115,069
Restricted cash	2,498	205
Total	$ 38,806	$ 115,274	$ 56,666

Summary of Significant Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2019
Property and Equipment, Net
Lease, Practical Expedients, Package [true false]	true
Laboratory equipment \| Minimum
Property and Equipment, Net
Estimated Useful Life	3 years
Laboratory equipment \| Maximum
Property and Equipment, Net
Estimated Useful Life	5 years
Computer equipment & software
Property and Equipment, Net
Estimated Useful Life	3 years
Furniture & fixtures
Property and Equipment, Net
Estimated Useful Life	5 years
Machinery & equipment \| Minimum
Property and Equipment, Net
Estimated Useful Life	3 years
Machinery & equipment \| Maximum
Property and Equipment, Net
Estimated Useful Life	5 years

Summary of Significant Accounting Policies - Misc (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) segment	Dec. 31, 2018 USD ($)
Number of operating segments \| segment	1
Adjustment for other than temporary decline in fair value \| $	$ 0	$ 0
Stock options
Expected dividend yield	0.00%

Summary of Significant Accounting Policies - Recently Issued Accounting Pronouncements (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Jan. 01, 2019
Significant accounting policies
Lease, Practical Expedients, Package [true false]	true
Operating lease liabilities	$ 5,303
Right-of-use assets	$ 4,447
ASU 2016-02 \| Restatement
Significant accounting policies
Operating lease liabilities		$ 6,200
Right-of-use assets		$ 5,400

Fair Value of Financial Assets and Liabilities - (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Marketable securities:
Warrant to purchase preferred stock converted into warrant to purchase common stock	7,614
Warrant purchase price	$ 3.94
Recurring
Assets:
Money market funds, included in cash and cash equivalents	$ 34,896	$ 114,593
Marketable securities:
U.S. Treasury obligations	121,140	60,576
Total assets	156,036	175,169
Recurring \| Level 1
Assets:
Money market funds, included in cash and cash equivalents	34,896	114,593
Marketable securities:
U.S. Treasury obligations	121,140	60,576
Total assets	$ 156,036	$ 175,169

Marketable Securities - Summary of Investments (Details) $ in Thousands	Dec. 31, 2019 USD ($) security	Dec. 31, 2018 USD ($) security
Marketable securities available-for-sale
Amortization Cost	$ 121,103	$ 60,584
Gross Unrealized Gains	39
Gross Unrealized Losses	(2)	(8)
Estimated Fair Value	121,140	60,576
Aggregate fair value of marketable securities with unrealized losses position for less than a year	$ 19,600	$ 60,600
Number of investments in an unrealized loss position for less than a year \| security	3	16
U.S. Treasury obligations
Marketable securities available-for-sale
Amortization Cost	$ 121,103	$ 60,584
Gross Unrealized Gains	39
Gross Unrealized Losses	(2)	(8)
Estimated Fair Value	$ 121,140	$ 60,576

Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Property and Equipment, Net
Property and equipment, gross	$ 7,729	$ 5,546
Less: Accumulated depreciation and amortization	(3,558)	(2,356)
Total property and equipment, net	4,171	3,190
Depreciation and amortization expense	1,303	807
Laboratory equipment
Property and Equipment, Net
Property and equipment, gross	5,432	3,585
Leasehold improvements
Property and Equipment, Net
Property and equipment, gross	1,580	1,578
Computer equipment & software
Property and Equipment, Net
Property and equipment, gross	423
Furniture & fixtures
Property and Equipment, Net
Property and equipment, gross	219	219
Machinery & equipment
Property and Equipment, Net
Property and equipment, gross	$ 75	75
Construction in progress
Property and Equipment, Net
Property and equipment, gross		$ 89

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Accrued Expenses
Accrued external research and development expense	$ 4,088	$ 3,284
Accrued payroll and related expenses	4,380	2,826
Accrued professional and consulting expense	929	890
Accrued other	213	157
Accrued expenses	$ 9,610	$ 7,157

Preferred Stock (Details) - $ / shares	Dec. 31, 2019	Dec. 31, 2018	May 29, 2018
Common Stock and Preferred Stock
Preferred stock, shares authorized	10,000,000	10,000,000	10,000,000
Preferred stock, par value	$ 0.001	$ 0.001	$ 0.001
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0

Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands		2 Months Ended	3 Months Ended	12 Months Ended
	May 29, 2018	Jul. 31, 2019	Jun. 30, 2018	Dec. 31, 2019	Dec. 31, 2018
Common Stock and Preferred Stock
Convertible preferred stock converted into shares			15,109,950
Increase in common stock authorized (in shares)	90,000,000
Common stock, shares authorized	150,000,000			150,000,000	150,000,000
Preferred stock, shares authorized	10,000,000			10,000,000	10,000,000
Preferred stock, par value	$ 0.001			$ 0.001	$ 0.001
Preferred stock, shares issued				0	0
Preferred stock, shares outstanding				0	0
Sale of common shares (in shares)		3,450,000	6,164,000
Purchase price (in dollars per share)		$ 15.00	$ 14.00
Proceeds from sale of common stock			$ 77,800	$ 48,348	$ 94,935
Warrant to purchase preferred stock converted into warrant to purchase common stock				7,614

Common Stock - Shares Reserved For Future Issuance (Details)	12 Months Ended
	Dec. 31, 2019 USD ($) Vote shares
Class of Stock [Line Items]
Number of votes per share \| Vote	1
Dividend declared or paid \| $	$ 0
Shares reserved for future issuance	5,591,380
2018 ESPP
Class of Stock [Line Items]
Shares reserved for future issuance	497,920
2018 Plan
Class of Stock [Line Items]
Shares reserved for future issuance	2,684,464
Stock options
Class of Stock [Line Items]
Shares reserved for future issuance	2,401,382
Warrant
Class of Stock [Line Items]
Shares reserved for future issuance	7,614

Equity-Based Compensation - 2018 Plan (Details)		12 Months Ended
Equity-Based Compensation - 2018 Plan (Details)	May 11, 2018 shares	Dec. 31, 2019 item	Dec. 31, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award
Number of share-based compensation plans \| item		3
2018 Plan
Share-based Compensation Arrangement by Share-based Payment Award
Additional shares authorized under stock-based plans (in shares)	352,204
Shares authorized for issuance	3,139,274
Increase as percentage of outstanding shares	4.00%
Vesting period	4 years
2017 Plan
Share-based Compensation Arrangement by Share-based Payment Award
Additional shares authorized under stock-based plans (in shares)	0
Shares authorized for issuance			3,455,330
Vesting period			4 years

Equity-Based Compensation - 2017 Plan (Details) - 2017 Plan	12 Months Ended
	Dec. 31, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	4 years
Shares authorized for issuance	3,455,330

Equity-Based Compensation - 2018 ESPP (Details) - 2018 ESPP - shares		12 Months Ended
	May 02, 2018	Dec. 31, 2019	May 11, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized for issuance			235,743
Additional shares authorized under stock-based plans (in shares)	353,614
Increase as percentage of outstanding shares	1.00%
Shares issued		0

Equity-Based Compensation - Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Equity-based compensation
Equity-based compensation expense	$ 7,972	$ 5,211
Equity-based compensation expense related to acceleration of equity awards	600
Equity-based compensation expense related to modifications of equity awards	100	1,200
Research and development expense
Equity-based compensation
Equity-based compensation expense	2,425	1,661
General and administrative expense
Equity-based compensation
Equity-based compensation expense	$ 5,547	$ 3,550

Equity-Based Compensation - Restricted stock (Details) - Restricted common stock $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($) $ / shares shares
Number of unvested awards
Outstanding, beginning (in shares) \| shares	664,174
Vested (in shares) \| shares	(357,604)
Forfeited (in shares) \| shares	(4,210)
Outstanding, end (in shares) \| shares	302,360
Weighted Average Fair Value
Outstanding, beginning (in dollars per share) \| $ / shares	$ 5.77
Vested (in dollars per share) \| $ / shares	5.77
Forfeited (in dollars per share) \| $ / shares	5.77
Outstanding, end (in dollars per share) \| $ / shares	$ 5.77
Unrecognized equity based compensation expense \| $	$ 1.3
Period for recognition	1 year 2 months 12 days

Equity-Based Compensation - Stock Options (Details) - Stock options - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Number of Units
Outstanding, beginning (in shares)	1,627,947
Granted (in shares)	1,034,825
Exercised (in shares)	(129,431)
Cancelled (in shares)	(131,959)
Outstanding, end (in shares)	2,401,382	1,627,947
Options exercisable, end (in shares)	787,537
Weighted Average Exercise Price
Outstanding, beginning (in dollars per share)	$ 10.86
Granted (in dollars per share)	15.07
Exercised (in dollars per share)	7.06
Cancelled (in dollars per share)	15.46
Outstanding, end (in dollars per share)	12.63	$ 10.86
Options exercisable, end (in dollars per share)	$ 11.17
Stock options
Weighted average remaining contractual term	8 years 4 months 10 days	9 years 3 months 4 days
Weighted average remaining contractual term, exercisable	7 years 4 months 24 days
Aggregate intrinsic value, beginning	$ 19,831
Aggregate intrinsic value, end	6,523	$ 19,831
Aggregate intrinsic value, exercisable	$ 2,902
Weighted average grant date fair value (in dollars per share)	$ 10.53

Equity-Based Compensation - Assumptions (Details) - Stock options $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Assumptions used in determining the fair value of options
Risk-free interest rate	2.31%
Expected dividend yield	0.00%
Expected term (years to liquidity)	6 years 2 months 12 days
Expected volatility	79.50%
Unrecognized equity-based compensation expense	$ 13.8
Period for recognition	2 years 7 months 6 days

Income Taxes - Reconciliation (Details)	12 Months Ended
Income Taxes - Reconciliation (Details)	Dec. 31, 2019	Dec. 31, 2018
Effective income tax rate
Tax effected at statutory rate	21.00%	21.00%
State taxes	7.20%	6.60%
Stock compensation	(1.70%)	(1.70%)
Non deductible expenses	(0.40%)	(0.10%)
Federal research and development credits	7.80%	5.90%
Change in valuation allowance	(33.90%)	(31.70%)

Income Taxes - Deferred Tax Assets (Liabilities) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Reserve and accruals	$ 1,704	$ 1,031
Net operating loss carryforwards	26,932	25,380
Deferred rent		242
Operating lease liability	1,448
Deferred revenue	13,173	3,525
Tax credits	9,569	4,976
Stock based compensation	1,049	314
Total gross deferred tax assets	53,875	35,468
Valuation allowance	(52,260)	(34,970)
Total deferred tax assets	1,615	498
Operating lease right-of-use asset	(1,214)
Fixed and intangible assets	(401)	(498)
Total deferred tax liabilities	$ (1,615)	$ (498)

Income Taxes - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income Tax Contingency
Increase in valuation allowance for deferred tax assets	$ 17.3	$ 19.2
Federal operating loss carryforwards without expiration date	47.6
Federal
Income Tax Contingency
Net operating loss carryforwards	98.1
Tax credit carryforward amount	8.0
State
Income Tax Contingency
Net operating loss carryforwards	100.1
Tax credit carryforward amount	$ 2.0

Commitments and Contingencies (Details) $ in Thousands	1 Months Ended	12 Months Ended
Commitments and Contingencies (Details) $ in Thousands	Feb. 28, 2018 USD ($) item	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Mar. 31, 2015
Leased assets
Rent for facility lease		$ 1,400	$ 1,000
Lease Cost:
Operating lease cost		1,375
Variable lease cost		674
Total lease cost		2,049
Operating cash flows used for operating leases		$ 1,266
Weighted average remaining lease term		3 years 9 months
Weighted average incremental borrowing rate		6.47%
Memorial Drive, Cambridge MA
Leased assets
Term of lease				5 years
Option to extend the term	true
Number of renewal options \| item	1
Renewal term	5 years
Memorial Drive, Cambridge MA \| Minimum
Leased assets
Rent for facility lease	$ 1,400
Memorial Drive, Cambridge MA \| Maximum
Leased assets
Rent for facility lease	$ 1,700

Commitments and Contingencies - Maturities (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Nov. 30, 2019	Dec. 31, 2019
Maturity analysis of the annual undiscounted cash flows
2020		$ 1,446
2021		1,619
2022		1,668
2023		1,279
Total lease payments		6,012
Less imputed interest		(709)
Total operating lease liabilities		5,303
Letter of credit		2,500
Binney St, Cambridge MA
Maturity analysis of the annual undiscounted cash flows
Incentive to lease	$ 14,100
Payments for tenant improvements		$ 0
Lease not yet commenced, option to extend the term	true
Lease not yet commenced, renewal term	2 years
Base rent	$ 6,900
Annual upward adjustment (as a percent)	3.50%
Letter of credit	$ 2,300

Loan Payable (Details) - SVB - USD ($)	12 Months Ended
Loan Payable (Details) - SVB - USD ($)	Dec. 31, 2019	Dec. 31, 2018	Aug. 31, 2015
Loan Payable
Line of credit maximum			$ 2,000,000
Amount borrowed		$ 400,000	$ 2,000,000
Interest expense	$ 27,000	$ 100,000

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References + Details

Agreements - Gilead (Details) $ / shares in Units, $ in Thousands		2 Months Ended	3 Months Ended	12 Months Ended
	Dec. 19, 2018 USD ($) item $ / shares shares	Jul. 31, 2019 $ / shares shares	Jun. 30, 2018 $ / shares shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Agreements
Accounts receivable				$ 25,000
Sale of common shares (in shares) \| shares		3,450,000	6,164,000
Purchase price (in dollars per share) \| $ / shares		$ 15.00	$ 14.00
Sale of common shares				48,348	$ 17,096
Revenue earned				20,492
Gilead
Agreements
Number of programs \| item	3
Option exercise period	90 days
Revenue proceeds	$ 50,000
Potential milestone payments	$ 475,000
Accounts receivable				25,000
Refundable payments under the agreement				0
Sale of common shares (in shares) \| shares	980,392
Purchase price (in dollars per share) \| $ / shares	$ 30.60
Sale of common shares	$ 30,000
Maximum number of program antibodies to be notified which satisfies development criteria \| item	2
Transaction price	$ 80,000
Research collaboration term	3 years
Equity investment included in transaction price	$ 17,100
Contract liability	62,900			67,400
Securities premium				12,900
Revenue earned				20,500
Deferred revenue recognized				$ 14,700
Gilead \| Maximum
Agreements
Potential milestone payments	$ 1,425,000

Agreements - Gilead obligation period (Details) - Gilead - USD ($) $ in Millions	Dec. 31, 2019	Dec. 19, 2018
Agreements
Contract liability	$ 67.4	$ 62.9
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Agreements
Expected to recognize remaining deferred revenue	2 years

Net Loss per Share - Basic and Diluted (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Loss per share
Net loss	$ (51,000)	$ (49,326)
Weighted average common shares outstanding, basic and diluted (in shares)	27,537,939	15,655,293
Net loss per share, basic and diluted (in dollars per share)	$ (1.85)	$ (3.15)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Net Loss per Share - Anti-dilutive (Details) - shares	12 Months Ended
Net Loss per Share - Anti-dilutive (Details) - shares	Dec. 31, 2019	Dec. 31, 2018
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of net loss per share	2,711,356	2,299,735
Restricted common stock
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of net loss per share	302,360	664,174
Warrant
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of net loss per share	7,614	7,614
Stock options
Anti-dilutive securities
Anti-dilutive securities excluded from the calculation of net loss per share	2,401,382	1,627,947

Retirement Plan (Details) - USD ($) $ in Thousands	12 Months Ended
Retirement Plan (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Retirement Plan
Company contributions	$ 0	$ 0