Aceragen (ACGN) 10-K 1 Mar 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 28, 2021	Jun. 30, 2020
Document and Entity Information
Document Type	10-K
Document Period End Date	Dec. 31, 2020
Document Annual Report	true
Document Transition Report	false
Entity File Number	001-31918
Entity Registrant Name	IDERA PHARMACEUTICALS, INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	04-3072298
Entity Address, Address Line One	505 Eagleview Blvd., Suite 212
Entity Address, City or Town	Exton
Entity Address, State or Province	PA
Entity Address, Postal Zip Code	19341
City Area Code	484
Local Phone Number	348-1600
Title of 12(b) Security	Common Stock, $.001 par value
Trading Symbol	IDRA
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
ICFR Auditor Attestation Flag	false
Entity Small Business	true
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		42,257,456
Entity Public Float			$ 52.7
Entity Central Index Key	0000861838
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false

BALANCE SHEETS

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 33,229	$ 40,019
Short-term investments	4,499	2,774
Prepaid expenses and other current assets	3,627	3,475
Total current assets	41,355	46,268
Property and equipment, net	44	97
Operating lease right-of-use assets	930	1,054
Other assets	70	70
Total assets	42,399	47,489
Current liabilities:
Accounts payable	329	457
Accrued expenses	6,072	7,461
Operating lease liability	191	163
Future tranche right liability		46,436
Other current liability	435
Total current liabilities	7,027	54,517
Warrant liability, long-term	6,983	3,241
Future tranche right liability, long-term	118,803
Operating lease liability, net of current portion	758	899
Total liabilities	133,571	58,657
Commitments and contingencies (Note 13)
Stockholders' equity (deficit):
Common stock, $0.001 par value, Authorized - 140,000 shares; Issued and outstanding - 35,219 and 29,672 at December 31, 2020 and December 31, 2019, respectively	38	30
Additional paid-in capital	742,342	709,692
Accumulated deficit	(833,552)	(720,890)
Total stockholders' deficit	(91,172)	(11,168)
Total liabilities and stockholders' deficit	42,399	47,489
Series B1 Redeemable Convertible Preferred Stock
Stockholders' equity (deficit):
Preferred stock
Series A Convertible Preferred Stock
Stockholders' equity (deficit):
Preferred stock

BALANCE SHEETS (Parenthetical)

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Preferred stock, shares issued	500,000
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	140,000,000	140,000,000
Common stock, shares issued	38,291,000	29,672,000
Common stock, shares outstanding	38,291,000	29,672,000
Series B1 Redeemable Convertible Preferred Stock
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares designated	277,921	278,000
Preferred stock, shares issued	24,000	24,000
Preferred stock, shares outstanding	24,000	24,000
Common stock, shares outstanding	24,000	24,000
Series A Convertible Preferred Stock
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares designated	1,500,000	1,500,000
Preferred stock, shares issued	1,000	1,000
Preferred stock, shares outstanding	655	655

STATEMENTS OF OPERATIONS

STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
STATEMENTS OF OPERATIONS
Alliance revenue		$ 1,448	$ 662
Revenue, Product and Service [Extensible List]	us_gaap:RevenueFromContractWithCustomerIncludingAssessedTax	us_gaap:RevenueFromContractWithCustomerIncludingAssessedTax	us_gaap:RevenueFromContractWithCustomerIncludingAssessedTax
Operating expenses:
Research and development	$ 24,772	$ 34,853	$ 41,841
General and administrative	11,915	12,481	15,420
Merger-related costs, net			1,245
Restructuring costs		181	3,112
Total operating expenses	36,687	47,515	61,618
Loss from operations	(36,687)	(46,067)	(60,956)
Other income (expense):
Interest income	165	1,150	1,089
Interest expense	(3)		(11)
Warrant revaluation loss	(3,742)	(598)
Future tranche right revaluation loss	(72,367)	(10,964)
Foreign currency exchange loss	(28)	(36)	(3)
Net loss	(112,662)	(56,515)	(59,881)
Deemed dividend related to December 2019 Private Placement (see Note 7)		(28,043)
Net loss attributable to common stockholders	$ (112,662)	$ (84,558)	$ (59,881)
Net loss per share applicable to common stockholders - basic and diluted (Note 17)	$ (3.33)	$ (2.96)	$ (2.25)
Weighted-average number of common shares used in computing net loss per share applicable to common stockholders - basic and diluted	33,821	28,545	26,601

STATEMENTS OF REDEEMABLE PREFER

STATEMENTS OF REDEEMABLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Series B1 Redeemable Convertible Preferred Stock	Total
Beginning balance at Dec. 31, 2017	$ 24	$ 712,165	$ (604,494)		$ 107,695
Beginning balance (in shares) at Dec. 31, 2017	24,453
Issuance of common stock under employee stock purchase plan		243			243
Issuance of common stock under employee stock purchase plan (in shares)	25
Issuance of common stock upon exercise of common stock options and warrants	$ 3	10,163			10,166
Issuance of common stock upon exercise of common stock options and warrants (in shares)	2,702
Issuance of common stock for services rendered		97			97
Issuance of common stock for services rendered (in shares)	8
Stock-based compensation expense		5,674			5,674
Net loss			(59,881)		(59,881)
Ending balance at Dec. 31, 2018	$ 27	728,342	(664,375)		63,994
Ending balance (in shares) at Dec. 31, 2018	27,188
Sale of common stock, net of issuance costs	$ 3	5,295			5,298
Sale of common stock, net of issuance costs (in shares)	2,068
Sale of redeemable convertible preferred stock				24
Deemed dividend related to December 2019 Private Placement (Note 7)		(28,043)			(28,043)
Issuance of commitment shares (in shares)	270
Issuance of common stock under employee stock purchase plan		121			121
Issuance of common stock under employee stock purchase plan (in shares)	61
Issuance of common stock upon exercise of common stock options and warrants		3			3
Issuance of common stock upon exercise of common stock options and warrants (in shares)	38
Issuance of common stock for services rendered		129			129
Issuance of common stock for services rendered (in shares)	47
Stock-based compensation expense		3,845			3,845
Net loss			(56,515)		(56,515)
Ending balance at Dec. 31, 2019	$ 30	709,692	(720,890)		$ (11,168)
Ending balance (in shares) at Dec. 31, 2019	29,672			24	29,672
Sale of common stock, net of issuance costs	$ 8	28,638			$ 28,646
Sale of common stock, net of issuance costs (in shares)	8,218
Issuance of common stock under equity incentive plan (vesting of restricted stock units) (in shares)	177
Issuance of common stock under employee stock purchase plan		113			113
Issuance of common stock under employee stock purchase plan (in shares)	76
Issuance of common stock upon exercise of warrants		15			15
Issuance of common stock upon exercise of warrants (in shares)	5
Issuance of common stock for services rendered		243			243
Issuance of common stock for services rendered (in shares)	143
Stock-based compensation expense		3,641			3,641
Net loss			(112,662)		(112,662)
Ending balance at Dec. 31, 2020	$ 38	$ 742,342	$ (833,552)		$ (91,172)
Ending balance (in shares) at Dec. 31, 2020	38,291			24	38,291

STATEMENTS OF CASH FLOWS

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash Flows from Operating Activities:
Net loss	$ (112,662)	$ (56,515)	$ (59,881)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	3,641	3,845	5,674
Warrant liability revaluation loss	3,742	598
Future tranche right liability revaluation loss	72,367	10,964
Issuance of common stock for services rendered	243	129	97
Accretion of discounts on short-term investments	(46)	(372)
Depreciation and amortization expense	61	120	432
(Gain) loss on disposal of property and equipment		(10)	477
Changes in operating assets and liabilities:
Prepaid expenses and other assets	500	(2,160)	2,717
Accounts payable, accrued expenses, and other liabilities	(1,629)	(1,105)	(866)
Deferred revenue			(566)
Other	11	8
Net cash used in operating activities	(33,772)	(44,498)	(51,916)
Cash Flows from Investing Activities:
Purchases of available-for-sale securities	(12,178)	(44,502)
Proceeds from maturity of available-for-sale securities	10,499	42,100
Proceeds from the sale of property and equipment		11	290
Purchases of property and equipment	(8)	(11)	(75)
Net cash (used in) provided by investing activities	(1,687)	(2,402)	215
Cash Flows from Financing Activities:
Proceeds from private placement		10,072
Proceeds from common stock financings, net	28,758	5,298
Proceeds from employee stock purchases	113	121	243
Proceeds from exercise of common stock options and warrants	15	3	10,166
Payments on note payable and seller-financed purchases	(217)		(209)
Other		(6)	(8)
Net cash provided by financing activities	28,669	15,488	10,192
Net decrease in cash and cash equivalents	(6,790)	(31,412)	(41,509)
Cash and cash equivalent, beginning of period	40,019	71,431	112,940
Cash and cash equivalents, end of period	33,229	40,019	71,431
Supplemental disclosure of cash flow information:
Cash paid for interest	3		9
Increase to operating lease right-of-use asset upon adoption of ASC 842		1,236
Increase to operating lease right-of-use assets upon acquisition	54
Increase to lease liability upon adoption of ASC 842		1,236
Increase to operating lease liability upon acquisition	54
Supplemental disclosure of non-cash financing and investing activities:
Offering costs in accounts payable and accrued expenses	112	$ 165	$ 101
Non-cash seller-financed purchases	$ 652

Business and Organization

Business and Organization	12 Months Ended
	Dec. 31, 2020
Business and Organization
Business and Organization	Note 1. Business and Organization ​ Business Overview ​ Idera Pharmaceuticals, Inc. (“Idera” or the “Company”), a Delaware corporation, is a clinical-stage biopharmaceutical company with a business strategy focused on the clinical development, and ultimately the commercialization, of drug candidates for both oncology and rare disease indications characterized by small, well-defined patient populations with serious unmet medical needs. The Company’s current focus is on its Toll-like receptor (“TLR”) agonist, tilsotolimod (IMO-2125), for oncology. The Company believes it can develop and commercialize targeted therapies on its own. To the extent the Company seeks to develop drug candidates for broader disease indications, it has entered into and may explore additional collaborative alliances to support development and commercialization. ​ Liquidity and Financial Condition ​ As of December 31, 2020, the Company had an accumulated deficit of $833.6 million and a cash, cash equivalents and short-term investments balance of $37.7 million. The Company expects to incur substantial operating losses in future periods and will require additional capital as it seeks to advance tilsotolimod and any future drug candidates through development to commercialization. The Company does not expect to generate product revenue, sales-based milestones or royalties until the Company successfully completes development of and obtains marketing approval for tilsotolimod or other future drug candidates, either alone or in collaboration with third parties, which the Company expects will take a number of years. In order to commercialize tilsotolimod and any future drug candidates, the Company needs to complete clinical development and comply with comprehensive regulatory requirements. The Company is subject to a number of risks and uncertainties similar to those of other companies of the same size within the biotechnology industry, such as uncertainty of clinical trial outcomes, uncertainty of additional funding and history of operating losses. ​ The Company follows the provisions of Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 205-40, Presentation of Financial Statements—Going Concern , which requires management to assess the Company’s ability to continue as a going concern within one year after the date the financial statements are issued. Management currently anticipates that the Company’s balance of cash, cash equivalents, and short-term investments on hand as of December 31, 2020, plus a total of $16.3 million of cash received in January and February 2021 from the ATM Agreement (Note 8) and the LPC Purchase Agreement (Note 8), is sufficient to enable the Company to continue as a going concern through the one-year period subsequent to the filing date of this Annual Report on Form 10-K and fund operations into the second quarter of 2022. The Company has and will continue to evaluate available alternatives to extend its operations beyond this date, which include raising additional capital through the Company’s December 2019 Securities Purchase Agreement (Note 7), LPC Agreement (Note 8), ATM Agreement (Note 8), April 2020 Securities Purchase Agreement (Note 8), July 2020 Securities Purchase Agreement (Note 8), or additional financing or strategic transactions. Additionally, management’s plans may also include the possible deferral of certain operating expenses unless additional capital is received. Management’s operating plan, which underlies the analysis of the Company’s ability to continue as a going concern, involves the estimation of the amount and timing of future cash inflows and outflows. Actual results could vary from the operating plan . ​

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	Note 2. Summary of Significant Accounting Policies ​ Basis of Presentation ​ The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”). ​ Use of Estimates ​ The preparation of financial statements in conformity with GAAP requires management to make estimates, judgements, and assumptions that affect the reported amounts of assets, liabilities, equity, revenues and expenses, and related disclosure of contingencies in the accompanying financial statements and these notes. In addition, management’s assessment of the Company’s ability to continue as a going concern involves the estimation of the amount and timing of future cash inflows and outflows. On an ongoing basis, the Company evaluates its estimates, judgments and methodologies. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable. Actual results could differ materially from those estimates. ​ Segment Information ​ Operating segments are defined as components of an enterprise in 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 assessing performance. The Company views its operations and manages its business as one operating segment, which is the business of developing novel therapeutics for oncology and rare diseases. ​ Financial Instruments ​ The fair value of the Company’s financial instruments is determined and disclosed in accordance with the three-tier fair value hierarchy specified in Note 3. The Company is required to disclose the estimated fair values of its financial instruments. As of December 31, 2020 and 2019, the Company’s financial instruments consisted of cash, cash equivalents, short-term investments, receivables, and warrant and future tranche right liabilities. The estimated fair values of these financial instruments approximate their carrying values as of December 31, 2020 and 2019. As of December 31, 2020, the Company did not have any other derivatives, hedging instruments or other similar financial instruments. ​ Concentration of Credit Risk ​ Financial instruments that subject the Company to credit risk primarily consist of cash, cash equivalents and short-term investments. The Company’s credit risk is managed by investing in highly rated money market instruments, U.S. treasury bills, corporate bonds, commercial paper and/or other debt securities. Due to these factors, no significant additional credit risk is believed by management to be inherent in the Company’s assets. As of December 31, 2020, all of the Company’s cash and cash equivalents were held at two financial institutions. ​ Cash and Cash Equivalents ​ The Company considers all highly liquid investments with maturities of 90 days or less when purchased to be “cash equivalents.” Cash and cash equivalents at December 31, 2020 and 2019 consisted of cash and money market funds. ​ Note 2. Summary of Significant Accounting Policies (Continued) ​ Property and Equipment ​ Property and equipment is carried at acquisition cost less accumulated depreciation, subject to review for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable as described further under the heading "Impairment of Long-Lived Assets" below. The cost of normal, recurring, or periodic repairs and maintenance activities related to property and equipment are expensed as incurred. The cost for planned major maintenance activities, including the related acquisition or construction of assets, is capitalized if the repair will result in future economic benefits. ​ Depreciation and amortization are computed using the straight-line method based on the estimated useful lives of the related assets. Leasehold improvements are amortized over the remaining lease term or the related useful life, if shorter. Equipment and other long-lived assets are depreciated over three to five years . ​ When an asset is disposed of, the associated cost and accumulated depreciation is removed from the related accounts on the Company's balance sheet with any resulting gain or loss included in the Company's statement of operations. ​ Operating Lease Right-of-use Asset and Lease Liability ​ The Company accounts for leases under ASC Topic 842, Leases . Operating leases are included in “Operating lease right-of-use assets” within the Company’s balance sheets and represent the Company’s right to use an underlying asset for the lease term. The Company’s related obligation to make lease payments are included in “Operating lease liability” and “Operating lease liability, net of current portion” within the Company’s balance sheets. Operating lease right-of-use (“ROU”) assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. As most of the Company’s leases do not provide an implicit rate, the Company uses 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. Lease expense for lease payments is recognized on a straight-line basis over the lease term. The ROU assets are tested for impairment according to ASC Topic 360, Property, Plant, and Equipment (“ASC 360”). Leases with an initial term of 12 months or less are not recorded on the balance sheet and are recognized as lease expense on a straight-line basis over the lease term. ​ As of December 31, 2020 and 2019, the Company’s operating lease ROU assets and corresponding short-term and long-term lease liabilities primarily relate to its existing Exton, PA facility operating lease which expires on May 31, 2025. ​ Impairment of Long-Lived Assets ​ In accordance with ASC 360-10-35, Impairment or Disposal of Long-Lived Assets , the Company reviews its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable (i.e. impaired). Once an impairment is determined, the actual impairment recognized is the difference between the carrying amount and the fair value (less costs to sell for assets to be disposed of) as estimated using one of the following approaches: income, cost and/or market. Fair value using the income approach is determined primarily using a discounted cash flow model that uses the estimated cash flows associated with the asset or asset group under review, discounted at a rate commensurate with the risk involved. Fair value utilizing the cost approach is determined based on the replacement cost of the asset reduced for, among other things, depreciation and obsolescence. Fair value, utilizing the market approach, benchmarks the fair value against the carrying amount. ​ Other Current Liability ​ In October 2020, the Company entered into a short-term financing arrangement with a third-party vendor to finance insurance premiums. The aggregate amount financed under this agreement was $0.6 million. As of December 31, 2020, the balance of $0.4 million, which is included in “Other current liability’ in the Company’s balance sheets, is scheduled to be paid in monthly installments through June 2021. ​ Note 2. Summary of Significant Accounting Policies (Continued) ​ Warrant Liability ​ The Company accounts for stock warrants as either equity instruments, liabilities or derivative liabilities in accordance with ASC 480, Distinguishing Liabilities from Equity (“ASC 480”) and/or ASC 815, Derivatives and Hedging (“ASC 815”), depending on the specific terms of the warrant agreement. Freestanding warrants for shares that are potentially redeemable, whereby the Company may be required to transfer assets (e.g. cash or other assets) outside of its control, are classified as liabilities. Liability-classified warrants are recorded at their estimated fair values at each reporting period until they are exercised, terminated, reclassified or otherwise settled. Changes in the estimated fair value of liability-classified warrants are recorded in Warrant Revaluation (Loss) Gain in the Company’s statements of operations. Equity classified warrants are recorded within additional paid-in capital at the time of issuance and not subject to remeasurement. For additional discussion on warrants, see Note 8. ​ Future Tranche Right Liability ​ On December 23, 2019, the Company entered into a Securities Purchase Agreement (the “December 2019 Securities Purchase Agreement”) with institutional investors affiliated with Baker Brothers (the “Purchasers”), an existing stockholder and related party (see Note 16). As more fully described in Note 7, the December 2019 Securities Purchase Agreement contains call options on redeemable preferred shares with warrants (conditionally exercisable for shares that are puttable). The Company determined that these call options represent freestanding financial instruments and accounts for the options as liabilities (“Future Tranche Right Liability”) under ASC 480, which requires the measurement and recognition of the fair value of the liability at the time of issuance and at each reporting period. Any change in fair value is recognized in Future Tranche Right Liability Revaluation (Loss) Gain in the Company’s statements of operations. ​ As of December 31, 2020, the Future Tranche Right Liability is classified as a long-term liability in the Company’s balance sheet as settlement is in the form of the applicable Series B convertible preferred stock and warrants exercisable for shares of either Series B1 Preferred Stock or the Company’s common stock. As of December 31, 2019, the Future Tranche Right Liability was classified as a current liability because the Future Tranche Rights and related Option Fee, each defined in Note 7, were subject to the Company obtaining required shareholder approval, which was obtained in May 2020. ​ Preferred Stock ​ The Company applies ASC 480 when determining the classification and measurement of its preferred stock. Preferred shares subject to mandatory redemption are classified as liability instruments and are measured at fair value. Conditionally redeemable preferred shares (including preferred shares that feature redemption rights that are either within the control of the holder or subject to redemption upon the occurrence of uncertain events not solely within the Company’s control) are classified as temporary equity. At all other times, preferred shares are classified as stockholders’ equity. ​ Accretion of redeemable convertible preferred stock includes the accretion of the Company's Series B redeemable convertible preferred stock to its stated value. The carrying value of the Series B redeemable convertible preferred stock is being accreted to redemption value using the effective interest method, from the date of issuance to the earliest date the holders can demand redemption. ​ Redeemable Preferred Stock Issued with Other Freestanding Instruments ​ The Company considers guidance within ASC 470-20, Debt (ASC 470), ASC 480, and ASC 815 when accounting for a redeemable equity instrument issued with other freestanding instruments (e.g. detachable warrants and future tranche right liabilities), such as in the December 2019 Private Placement (Note 7). In circumstances in which redeemable convertible preferred stock is issued with freestanding liability-classified instruments, the proceeds from the issuance of the convertible preferred stock are first allocated to those instruments at their full estimated fair value. The remaining proceeds, as further reduced by discounts created by the bifurcation of embedded derivatives and/or beneficial conversion features, if any, are allocated to the redeemable equity instrument. ​ Note 2. Summary of Significant Accounting Policies (Continued) ​ Revenue Recognition ​ The Company recognizes revenue in accordance with ASC Topic 606, Revenue from Contracts with Customers (“ASC 606’), which applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. In accordance with ASC 606, the Company 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 revenue recognition for arrangements that the Company determines are within the scope of ASC Topic 606, it performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. ​ The Company only applies the five-step model to contracts when it determines that it is probable it will collect the consideration to which it is entitled 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. ​ Amounts received prior to satisfying the revenue recognition criteria are recognized as deferred revenue in the Company’s balance sheet. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current portion of deferred revenue. 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. ​ Alliance Revenues The Company’s revenues have primarily been generated through collaborative research, development and/or commercialization agreements. The terms of these agreements may include payment to the Company of one or more of the following: nonrefundable, up-front license fees; research, development and commercial milestone payments; and other contingent payments due based on the activities of the counterparty or the reimbursement by licensees of costs associated with patent maintenance. Each of these types of revenue are recorded as Alliance revenues in the Company’s statements of operations. 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. ​ ​ Note 2. Summary of Significant Accounting Policies (Continued) ​ See Note 10, “Collaboration and License Agreements” for additional details regarding the Company’s collaboration and out-licensing arrangements. As part of the accounting for these arrangements, the Company allocates the transaction price to each performance obligation on a relative stand-alone selling price basis. The stand-alone selling price may be, but is not presumed to be, the contract price. In determining the allocation, the Company maximizes the use of observable inputs. When the stand-alone selling price of a good or service is not directly observable, the Company estimates the stand-alone selling price for each performance obligation using assumptions that require judgment. Acceptable estimation methods include, but are not limited to: (i) the adjusted market assessment approach, (ii) the expected cost plus margin approach, and (iii) the residual approach (when the stand-alone selling price is not directly observable and is either highly variable or uncertain). In order for the residual approach to be used, the Company must demonstrate that (a) there are observable stand-alone selling prices for one or more of the performance obligations and (b) one of the two criteria in ASC 606-10-32-34(c)(1) and (2) is met. The residual approach cannot be used if it would result in a stand-alone selling price of zero for a performance obligation as a performance obligation, by definition, has value on a stand-alone basis. ​ An option in a contract to acquire additional goods or services gives rise to a performance obligation only if the option provides a material right to the customer that it would not receive without entering into that contract. Factors that the Company considers in evaluating whether an option represents a material right include, but are not limited to: (i) the overall objective of the arrangement, (ii) the benefit the collaborator might obtain from the arrangement without exercising the option, (iii) the cost to exercise the option (e.g. priced at a significant and incremental discount) and (iv) the likelihood that the option will be exercised. With respect to options determined to be performance obligations, the Company recognizes revenue when those future goods or services are transferred or when the options expire. ​ The Company’s revenue arrangements may include the following: Up-front License Fees: If a license is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from nonrefundable, up-front fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled 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 from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments: At the inception of an agreement that includes research and development milestone payments, the Company evaluates whether each milestone is 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 transaction price is then 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. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such milestones and any related 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 Alliance revenues and earnings in the period of adjustment. Research and Development Activities: If the Company is entitled to reimbursement from its collaborators for specified research and development activities or the reimbursement of costs associated with patent maintenance, the Company determines whether such funding would result in Alliance revenues or an offset to research and development expenses. Reimbursement of patent maintenance costs are recognized during the period in which the related expenses are incurred as Alliance revenues in the Company’s statements of operations. ​ Note 2. Summary of Significant Accounting Policies (Continued) ​ Royalties: If the Company is entitled to receive sales-based royalties from its collaborator, including milestone payments based on the 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, provided the reported sales are reliably measurable, 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 collaboration and license arrangements. Manufacturing Supply and Research Services: Arrangements that include a promise for future supply of drug substance, drug product or research services at the licensee’s discretion are generally considered as options. The Company assesses if these options provide a material right to the licensee and if so, they are accounted for as separate performance obligations. If the Company is entitled to additional payments when the licensee exercises these options, any additional payments are recorded in Alliance revenues when the licensee obtains control of the goods, which is upon delivery, or as the services are performed. The Company receives payments from its licensees based on schedules established in each contract. Upfront payments and fees are recorded as deferred revenue upon receipt, and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less. ​ Research and Development Expenses ​ All research and development expenses are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including drug development trials and studies, drug manufacturing, laboratory supplies, external research, payroll including stock-based compensation and overhead. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are accepted by the Company or the services are performed. As of December 31, 2020 and 2019, the Company recorded approximately $2.5 million and $2.8 million as prepaid research and development, respectively, which is included within prepaid expenses and other current assets in the accompanying balance sheets. ​ Stock-Based Compensation ​ The Company accounts for stock-based compensation using ASC 718, Compensation – Stock Compensation (“ASC 718”), or ASC 505-50, Equity – Equity Based Payments to Non-Employees , as applicable. The Company accounts for stock-based awards to employees and non-employee directors using the fair value based method to determine compensation expense for all arrangements where shares of stock or equity instruments are issued for compensation. In addition, the Company accounts for stock-based compensation to other non-employees in accordance with the accounting guidance for equity instruments that are issued to entities or persons other than employees. ​ The Company recognizes all share-based payments to employees and directors as expense in the statements of operations based on their fair values. The Company records compensation expense on a straight-line basis over an award’s requisite service period, or vesting period, based on the award’s fair value at the date of grant. Vesting for time-based options and restricted stock units is generally four years for employees and one year for directors. The Company uses a Black-Scholes option-pricing model to determine the fair value of each option grant as of the date of grant for expense incurred. The Black-Scholes option pricing model requires inputs for risk-free interest rate, dividend yield, expected stock price volatility and expected term of the options. Forfeitures are accounted for as they occur. See Note 12, “Stock-based Compensation” for additional details. ​ ​ Note 2. Summary of Significant Accounting Policies (Continued) ​ Merger-related Costs, net On January 21, 2018, the Company, BioCryst Pharmaceuticals, Inc., a Delaware corporation (“BioCryst”), Nautilus Holdco, Inc., a Delaware corporation and a direct, wholly owned subsidiary of BioCryst (“Holdco”), Island Merger Sub, Inc., a Delaware corporation and a direct, wholly owned subsidiary of Holdco, and Boat Merger Sub, Inc., a Delaware corporation and a direct, wholly owned subsidiary of Holdco, entered into an Agreement and Plan of Merger (the “Merger Agreement”). The board of directors of each of Idera and BioCryst unanimously approved the Merger Agreement and the transactions contemplated thereby and the required regulatory approvals were received. However, the proposed merger was subject to approval by the stockholders of Idera and BioCryst, and satisfaction of other customary closing conditions, as specified in the Merger Agreement. At a special meeting of BioCryst stockholders held on July 10, 2018, BioCryst’s stockholders voted against the adoption of the Merger Agreement. Following such vote and in accordance with the terms of the Merger Agreement, BioCryst terminated the Merger Agreement. In accordance with the Merger Agreement, BioCryst paid the Company a fixed expense reimbursement amount of $6 million in July 2018 in connection with the termination of the Merger Agreement. The fixed expense reimbursement amount is included in “Merger-related costs, net” in the accompanying statements of operations. ​ Merger-related costs, net includes amounts related to the transactions contemplated under the Merger Agreement, including charges incurred for transaction and integration-related professional fees, employee retention costs, and other incremental costs directly related to the potential merger; less the $6 million fixed expense reimbursement termination fee, which was received by the Company in July 2018. ​ Restructuring Costs Restructuring charges are primarily comprised of severance costs related to workforce reductions, contract termination and wind-down costs and asset impairments. In accordance with ASC 420, Exit or Disposal Cost Obligations , the Company recognizes restructuring charges when the liability has been incurred, except for one-time employee termination benefits that are incurred over time. Generally, one-time employee termination benefits (i.e. severance costs) are accrued at the date management has committed to a plan of termination and employees have been notified of their termination dates and expected severance payments. Other costs will be recorded as incurred. Asset impairment charges have been, and will be, recognized when management has concluded that the assets have been impaired in accordance with ASC 360-10-35, Impairment or Disposal of Long-Lived Assets , or other applicable authoritative guidance. See Note 11 for additional details. ​ Income Taxes ​ An asset and liability approach is used for financial accounting and reporting for income taxes. Deferred income taxes arise from temporary differences between income tax and financial reporting and principally relate to recognition of revenue and expenses in different periods for financial and tax accounting purposes and are measured using currently enacted tax rates and laws. In addition, a deferred tax asset can be generated by a net operating loss carryover. If it is more likely than not that some portion or all of a deferred tax asset will not be realized, a valuation allowance is recognized. ​ In the event the Company is charged interest or penalties related to income tax matters, the Company would record such interest as interest expense and would record such penalties as other expense in the Statements of Operations. No such charges have been incurred by the Company. For each of the years ended December 31, 2020, 2019 and 2018, the Company had no uncertain tax positions. See Note 14, “Income Taxes” for additional details. ​ ​ Note 2. Summary of Significant Accounting Policies (Continued) ​ Net Loss per Common Share applicable to Common Stockholders ​ Basic and diluted net loss per common share applicable to common stockholders is computed using the weighted average number of shares of common stock outstanding during the period. The diluted loss per share calculation gives effect to dilutive stock options, restricted stock units, warrants, convertible preferred stock and other potentially dilutive common stock equivalents outstanding during the period. Diluted loss per share is based on the if-converted method or the treasury stock method, as applicable, and includes the effect from the potential issuance of common stock, such as shares issuable pursuant to the conversion of convertible preferred stock and the exercise of stock options and warrants, assuming the exercise of all “in-the-money” common stock equivalents based on the average market price during the period. Common stock equivalents have been excluded where their inclusion would be anti-dilutive. Diluted net loss per common share applicable to common stockholders is the same as basic net loss per common share applicable to common stockholders for each of the three years in the period ended December 31, 2020 as the effects of the Company’s potential common stock equivalents are antidilutive (see Note 17). ​ New Accounting Pronouncements ​ From time to time, new accounting pronouncements are issued by the FASB and rules are issued by the SEC that the Company has or will adopt as of a specified date. Unless otherwise noted, management does not believe that any other recently issued accounting pronouncements issued by the FASB or guidance issued by the SEC had, or is expected to have, a material impact on the Company’s present or future financial statements. ​ Recently Adopted Accounting Pronouncements ​ In June 2016, the FASB issued Accounting Standard Update (“ASU”) No. 2016-13, Financial Instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). This standard requires that credit losses be reported using an expected losses model rather than the incurred losses model that is currently used, and establishes additional disclosures related to credit risks. For available-for-sale debt securities with unrealized losses, this standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. The Company adopted ASU 2016-13 in the first quarter of 2020. The adoption of this ASU did not have a material effect on the Company’s financial statements. ​ In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework — Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”), which amends ASC 820, Fair Value Measurement . ASU 2018-13 modifies the disclosure requirements for fair value measurements by removing, modifying, or adding certain disclosures. The Company adopted ASU 2018-13 in the first quarter of 2020. The adoption of this ASU did not have a material effect on the Company’s financial statements. ​ Recently Issued (Not Yet Adopted) Accounting Pronouncements ​ In August 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU 2020-06”), which simplifies the guidance on an issuer’s accounting for convertible instruments and contracts in its own equity. The provisions of ASU 2020-06 are applicable for fiscal years beginning after December 15, 2021, with early adoption permitted no earlier than fiscal years beginning after December 15, 2020. The Company is currently evaluating the impact of ASU 2020-

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Measurements
Fair Value Measurements	Note 3. Fair Value Measurements ​ Assets and Liabilities Measured at Fair Value on a Recurring Basis ​ The Company applies the guidance in ASC 820, Fair Value Measurement , to account for financial assets and liabilities measured on a recurring basis. Fair value is measured at the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. As such, fair value is a market-based measurement that is determined based on assumptions that market participants would use in pricing an asset or liability. ​ The Company uses a fair value hierarchy, which distinguishes between assumptions based on market data (observable inputs) and an entity's own assumptions (unobservable inputs). The guidance requires that fair value measurements be classified and disclosed in one of the following three categories: ​ ● Level 1: Unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities; ● Level 2: Quoted prices in markets that are not active or inputs which are observable, either directly or indirectly, for substantially the full term of the asset or liability; ● Level 3: Prices or valuation techniques that require inputs that are both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity). ​ Determining which category an asset or liability falls within the hierarchy requires significant judgment. The Company evaluates its hierarchy disclosures each reporting period. There were no transfers between Level 1 , 2 and 3 during the year ended December 31 , 2020 . ​ The table below presents the assets and liabilities measured and recorded in the financial statements at fair value on a recurring basis at December 31, 2020 and 2019 categorized by the level of inputs used in the valuation of each asset and liability. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 (In thousands) ​ Total ​ Level 1 ​ Level 2 ​ Level 3 Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash ​ $ 250 ​ $ 250 ​ $ — ​ $ — ​ Cash equivalents – money market funds ​ ​ 32,979 ​ ​ 32,979 ​ ​ — ​ ​ — ​ Short-term investments – commercial paper ​ 3,499 ​ — ​ 3,499 ​ — ​ Short-term investments – US treasury bills ​ 1,000 ​ — ​ 1,000 ​ — ​ Total assets ​ $ 37,728 ​ $ 33,229 ​ $ 4,499 ​ $ — ​ Liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Warrant liability ​ $ 6,983 ​ $ — ​ $ — ​ $ 6,983 ​ Future tranche right liability ​ ​ 118,803 ​ ​ — ​ ​ — ​ ​ 118,803 ​ Total liabilities ​ $ 125,786 ​ $ — ​ $ — ​ $ 125,786 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ (In thousands) ​ Total ​ Level 1 ​ Level 2 ​ Level 3 ​ Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash ​ $ 250 ​ $ 250 ​ $ — ​ $ — ​ Cash equivalents – money market funds ​ ​ 39,769 ​ ​ 39,769 ​ ​ — ​ ​ — ​ Short-term investments – commercial paper ​ 2,774 ​ — ​ 2,774 ​ — ​ Total assets ​ $ 42,793 ​ $ 40,019 ​ $ 2,774 ​ $ — ​ Liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Warrant liability ​ $ 3,241 ​ $ — ​ $ — ​ $ 3,241 ​ Future tranche right liability ​ ​ 46,436 ​ ​ — ​ ​ — ​ ​ 46,436 ​ Total liabilities ​ $ 49,677 ​ $ — ​ $ — ​ $ 49,677 ​ ​ Note 3. Fair Value Measurements (Continued) ​ The Level 1 assets consist of money market funds, which are actively traded daily. The Level 2 assets consist of commercial paper and US treasury bills whose fair value may not represent actual transactions of identical securities. The fair value of commercial paper is generally determined based on the relationship between the investment’s discount rate and the discount rates of the same issuer’s commercial paper available in the market which may not be actively traded daily. Since these fair values may not be based upon actual transactions of identical securities, they are classified as Level 2. ​ Changes in Level 3 Liabilities Measured at Fair Value on a Recurring Basis ​ Warrant Liability and Future Tranche Right Liability ​ The reconciliation of the Company's warrant and future tranche right liability measured at fair value on a recurring basis using unobservable inputs (Level 3) is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Future ​ ​ Warrant ​ Tranche Right (In thousands) ​ Liability ​ Liability Balance, December 31, 2019 $ 3,241 ​ $ 46,436 Change in the fair value of liability 3,742 ​ 72,367 Balance, December 31, 2020 $ 6,983 ​ $ 118,803 ​ Assumptions Used in Determining Fair Value of Liability-Classified Warrants ​ The Company utilizes an option pricing model to value its liability-classified warrants. Inherent in the valuation model are assumptions related to volatility, risk-free interest rate, expected term, dividend rate, and other scenarios (i.e. probability of complex features of the warrants being triggered) . ​ The fair value of the warrants has been estimated with the following weighted-average assumptions: ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 ​ 2019 Risk-free interest rate ​ 0.50% ​ ​ 1.79% Expected dividend yield ​ — ​ ​ — Expected term (years) ​ 5.98 ​ ​ 6.98 Expected volatility ​ 80% ​ ​ 80% Exercise price (per share) $ 1.52 ​ $ 1.52 ​ Assumptions Used in Determining Fair Value of Future Tranche Rights ​ Th e Company utilizes a lattice model to value the Series B2 and B3 future tranche rights and a Monte Carlo simulation to value the Series B4 future tranche rights. The Company selected these models as it believes they are reflective of all significant assumptions that market participants would likely consider in negotiating the transfer of the Future Tranche Rights (as defined in Note 7). Such assumptions include, among other inputs, stock price volatility, risk-free rates, and expected terms inclusive of early exercise and cancellation assumptions . ​ The estimated fair value of the Future Tranche Rights is determined using Level 2 and Level 3 inputs. Significant inputs and assumptions used in the valuation models are as follows: ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 ​ 2019 Risk-free interest rate ​ 0.64% - 0.73% ​ ​ 1.84% - 1.88% Expected dividend yield ​ — ​ ​ — Expected term (years) of call options on preferred stock ​ 0.25 - 1.12 ​ ​ 1.16 - 2.16 Expected term (years) of warrants ​ 7.25 - 8.12 ​ ​ 8.16 - 9.16 Expected volatility ​ 80% ​ ​ 80% Exercise price (per share) for common stock equivalent for preferred stock and warrant $ 1.52 - 1.82 ​ $ 1.52 - 1.82 ​ ​

Investments

Investments	12 Months Ended
	Dec. 31, 2020
Investments
Investments	Note 4. Investments The Company’s available-for-sale investments at fair value consisted of the following at December 31, 2020 and 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ Gross Gross Estimated ​ ​ ​ ​ Unrealized ​ Unrealized ​ Fair ​ (In thousands) ​ Cost ​ (Losses) ​ Gains ​ Value ​ Short-term investments – commercial paper ​ $ 3,499 ​ $ — ​ $ — ​ $ 3,499 ​ Short-term investments – US treasury bills ​ ​ 1,000 ​ ​ — ​ ​ — ​ ​ 1,000 ​ Total short-term investments ​ $ 4,499 ​ $ — ​ $ — ​ $ 4,499 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ ​ ​ ​ ​ Unrealized ​ Unrealized ​ Fair (In thousands) Cost (Losses) Gains Value Short-term investments – commercial paper ​ $ 2,774 ​ $ — ​ $ — ​ $ 2,774 ​ Total short-term investments ​ $ 2,774 ​ $ — ​ $ — ​ $ 2,774 ​ ​ The Company had no realized gains or losses from the sale of investments in available-for-sale securities during each of the years ended December 31, 2020 and 2019. In accordance with ASU 2016-13, if the fair value of the Company’s investments in available-for-sale debt securities is less than the amortized cost, the Company records (i) an allowance for credit losses with a corresponding charge to net income (loss) for any credit-related impairment, with subsequent improvements in expected credit losses recognized as a reversal of the allowance, and/or (ii) any non-credit impairment loss to other comprehensive income (loss). ​ As of December 31, 2020 and 2019, the Company had no allowance for credit losses pertaining to the Company’s investments in available-for-sale debt securities. Additionally, there were no impairment charges or recoveries recorded during each of the years ended December 31, 2020 and 2019.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2020
Property and Equipment
Property and Equipment	Note 5. Property and Equipment ​ At December 31, 2020 and 2019, net property and equipment at cost consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ (In thousands) 2020 2019 Leasehold improvements ​ $ 107 ​ $ 107 ​ Equipment and other ​ 770 ​ 764 ​ Total property and equipment, at cost ​ $ 877 ​ $ 871 ​ Less: Accumulated depreciation and amortization ​ 833 ​ 774 ​ Property and equipment, net ​ $ 44 ​ $ 97 ​ ​ Depreciation and amortization expense on property and equipment was approximately $0.1 million, $0.1 million, and $0.4 million in 2020, 2019 and 2018, respectively. ​ No impairment charges were recognized during the years ended December 31, 2020 or 2019. During the year ended December 31, 2018, the Company recorded asset impairments related to its property equipment in the amount of $0.5 million in connection with restructuring activities more fully described in Note 11.

Accrued Expenses

Accrued Expenses	12 Months Ended
	Dec. 31, 2020
Accrued Expenses
Accrued Expenses	Note 6. Accrued Expenses ​ At December 31, 2020 and 2019, accrued expenses consisted of the following: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, (In thousands) ​ 2020 2019 Payroll and related costs ​ $ 2,133 ​ $ 2,179 ​ Clinical and nonclinical trial expenses ​ 3,229 ​ 4,199 ​ Professional and consulting fees ​ 584 ​ 859 ​ Restructuring expenses ​ — ​ 113 ​ Other ​ 126 ​ 111 ​ Total accrued expenses ​ $ 6,072 ​ $ 7,461 ​ ​

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2020
Redeemable Convertible Preferred Stock
Redeemable Convertible Preferred Stock	Note 7. Redeemable Convertible Preferred Stock ​ December 2019 Private Placement ​ On December 23, 2019, the Company entered into the December 2019 Securities Purchase Agreement, under which the Company sold 23,684 shares of Series B1 convertible preferred stock (“Series B1 Preferred Stock”) and warrants to purchase 2,368,400 shares of the Company’s common stock at an exercise price of $1.52 per share (or, if the holder elects to exercise the warrants for shares of Series B1 Preferred Stock, 23,684 shares of Series B1 Preferred Stock at an exercise price of $152 per share) for aggregate gross proceeds of $3.9 million (the “Initial Closing”). ​ In addition, the Company has agreed to sell to the Purchasers, at their option and subject to certain conditions, shares of Series B2 convertible preferred stock (“Series B2 Preferred Stock”), Series B3 convertible preferred stock (“Series B3 Preferred Stock”) and Series B4 convertible preferred stock (“Series B4 Preferred Stock) and accompanying warrants to purchase common stock (or preferred stock at the election of the holder) over a 21-month period following stockholder approval for the Charter Amendment, as defined below (the “Future Tranche Rights”). As of December 31, 2020, the Company’s outstanding Future Tranche Rights are as follows : ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Price Per ​ Aggregate Future Tranche Rights ​ Preferred Shares ​ Share ​ Purchase Price Tranche 2 (Series B2) (1) ​ 98,685 ​ $ 152 ​ $ 15,000,120 Tranche 3 (Series B3) (2) ​ 82,418 ​ $ 182 ​ ​ 15,000,076 Tranche 4 (Series B4) (2) ​ 82,418 ​ $ 182 ​ ​ 15,000,076 Total ​ 263,521 ​ ​ ​ ​ $ 45,000,272 (1) Accompanied by related warrants to purchase up to 9,868,500 shares of the Company’s common stock (or, if the holder elects to exercise the warrants for shares of Series B1 Preferred Stock, 98,685 shares of Series B1 Preferred Stock), at an exercise price of $1.52 per share (or, if the holder elects to exercise the warrants for Series B1 Preferred Stock, $152 per share of Series B1 Preferred Stock). (2) Accompanied by related warrants to purchase up to 6,593,440 shares of the Company’s common stock (or, if the holder elects to exercise the warrants for shares of Series B1 Preferred Stock, 65,934 shares of Series B1 Preferred Stock), at an exercise price of $1.82 per share (or, if the holder elects to exercise the warrants for Series B1 Preferred Stock, $182 per share of Series B1 Preferred Stock). ​ As consideration for the Future Tranche Rights, the Company received aggregate gross proceeds of $6.2 million (the “Option Fee”) in December 2019. Following the Company’s 2020 Annual Meeting of Stockholders held on May 12, 2020, where stockholders of the Company voted to approve an amendment to the Company’s Restated Certificate of Incorporation to increase the authorized number of shares of the Company’s common stock to 140,000,000 (the “Charter Amendment”), the Company is not required to return the Option Fee. ​ ​ ​ Note 7. Redeemable Convertible Preferred Stock ​ The purchase and sale of the securities issuable under tranches 2, 3 and 4 may occur in up to three separate closings, each to be conducted at the Purchasers’ discretion. The right of the Purchasers to purchase Series B2, Series B3 and Series B4 Preferred Stock will expire on the 10 th business day following the Company’s ORR Data Announcement, as defined in the December 2019 Securities Purchase Agreement, for its ILLUMINATE-301 study , August 12, 2021, and February 12, 2022, respectively. However, the Purchasers’ right to purchase securities under tranches 3 and 4 is contingent on the purchase of all of the securities in each preceding tranche right. In the event the Purchasers do not purchase all of the securities in a given tranche, their right to purchase shares in future tranches terminates and any outstanding warrants issued under the December 2019 Securities Purchase Agreement would terminate. Additionally, the Company has the right to decline the Series B4 Preferred Stock investment if its common stock trades at $7.60 for 20 days out of 30 days subsequent to the closing of the Series B3 Preferred Stock investment. ​ In addition to the aggregate gross proceeds received from the Initial Closing and the Option Fee, the Company is eligible to receive aggregate gross proceeds of up to an additional $87.6 million under the December 2019 Securities Purchase Agreement. ​ Accounting Considerations ​ The Company determined that the Series B1 Preferred Stock, the accompanying Series B1 warrants, and each of the Future Tranche Rights represent freestanding financial instruments. The warrants and the Future Tranche Rights are liability classified as the underlying shares are potentially redeemable and such redemption is deemed to be outside of the Company’s control. The $10.1 million in gross proceeds received in December 2019 was allocated to the Series B1 warrants and the Future Tranche Rights based on their estimated fair values of $2.6 million and $35.5 million, respectively. The excess fair value of $28.0 million over the gross proceeds received of $10.1 million was recorded as a deemed dividend to Baker Brothers, an existing significant shareholder. Costs incurred in connection with the December 2019 Securities Purchase Agreement were expensed as incurred. ​ Due to the redeemable nature of the Series B1 Preferred Stock, the Series B1 Preferred Stock has been classified as temporary equity. While the Series B1 Preferred Stock is not currently redeemable, it will become redeemable either on (i) the fifth anniversary of the initial issue date, or December 23, 2024, provided that certain events (the “Redemption Loss Events”) do not occur first or (ii) upon a liquidation or deemed liquidation event, provided that certain events (the “Liquidation Loss Events”) do not occur first. The Company cannot assess the probability of whether the Redemption Loss Events will occur prior to the fifth anniversary of the initial issue date, if ever, as certain factors triggering such events are outside the control of the Company. Accordingly, the carrying value of the Series B1 Preferred Stock is currently being accreted to its redemption value. In the event the holders of the Series B1 Preferred Stock lose their right to request redemption, the Series B Preferred Stock will no longer be accreted to its redemption value until redemption upon a liquidation event is deemed probable. For the years ended December 31, 2020 and 2019, accretion was de minimis.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Stockholders' Equity
Stockholders' Equity	Note 8. Stockholders’ Equity ​ Preferred Stock ​ The Restated Certificate of Incorporation, as amended, of the Company permits its board of directors to issue up to 5,000,000 shares of preferred stock, par value $0.01 per share, in one or more series, to designate the number of shares constituting such series, and fix by resolution, the powers, privileges, preferences and relative, optional or special rights thereof, including liquidation preferences and dividends, and conversion and redemption rights of each such series. ​ As of December 31, 2020, the Company has designated the following class of preferred stock: ● Series A: 1,500,000 authorized shares of Series A Convertible Preferred Stock ● Series B1: 277,921 authorized shares of Series B1 Redeemable Convertible Preferred Stock ● Series B2: 98,685 authorized shares of Series B2 Redeemable Convertible Preferred Stock ● Series B3: 82,814 authorized shares of Series B3 Redeemable Convertible Preferred Stock ● Series B4: 82,814 authorized shares of Series B4 Redeemable Convertible Preferred Stock ​ Series A Convertible Preferred Stock . The dividends on the Series A convertible preferred stock (“Series A Preferred Stock”) are payable semi-annually in arrears at the rate of 1% per annum, at the election of the Company, either in cash or additional duly designated, fully paid and nonassessable shares of Series A Preferred Stock. In the event of liquidation, dissolution or winding up of the Company, after payment of debts and other liabilities of the Company, the holders of the Series A Preferred Stock then outstanding will be entitled to a distribution of $1 per share out of any assets available to shareholders. The Series A Preferred Stock is non-voting. All remaining shares of Series A Preferred Stock rank, as to payment upon the occurrence of any liquidation event, senior to the Company’s common stock. Shares of Series A Preferred Stock are convertible, in whole or in part, at the option of the holder into fully paid and nonassessable shares of common stock at $272.00 per share, subject to adjustment. As of December 31, 2020 and 2019, there were 655 shares of Series A Preferred Stock outstanding. ​ Series B1, B2, B3 and B4 Convertible Preferred Stock . Holders of Series B1 Preferred Stock, Series B2 Preferred Stock, Series B3 Preferred Stock and Series B4 Preferred Stock (collectively, the “B1/B2/B3/B4 Preferred Stock”) are entitled to the amount of dividends, if and when declared, as would be payable to holders of common stock on an “as converted” basis (e.g. participating dividends). Until the applicable Transition Date (defined below), in the event of a liquidation event or deemed liquidation event, after payment of debts and other liabilities of the Company, the holders of the Series B1/B2/B3/B4 Preferred Stock then outstanding will be entitled to a distribution equal to the then applicable stated value per share of the Series B1/B2/B3/B4 Preferred Stock. Additionally, until the applicable Transition Date (defined below), at any time on or after the date that is the fifth (5th) anniversary of the initial issue date of the applicable series of preferred stock, all or any portion of the preferred stock is redeemable at the option of the holder at a redemption price of $152.00 per share (for Series B1 and Series B2 Preferred Stock) and $182.00 per share (for Series B3 and Series B4 Preferred Stock). The “Transition Date” means: ​ a) With respect to the Series B1 Preferred Stock, the first date following December 23, 2021, on which each of the Conditions (as defined below) is met (the “Series B1 Transition Date”); and ​ b) With respect to the Series B2 Preferred Stock, Series B3 Preferred Stock and Series B4 Preferred Stock, the first date following the two-year anniversary of the applicable series of preferred stock’s initial issue date, on which each of the Conditions (as defined below) is met (the “Series B2 Transition Date”). ​ ​ ​ ​ ​ Note 8. Stockholders’ Equity (Continued) ​ The “Conditions” shall mean: (a) the closing price of the Company’s common stock has been equal to or exceeded the price that is equal to three times (3x) the applicable series of preferred stock’s conversion price ( $1.52 for Series B1 Preferred Stock and B2 Preferred Stock; $1.82 for Series B3 Preferred Stock and Series B4 Preferred Stock) for 180 calendar days; (b) the 50 -day average trading volume of the Company’s common stock is greater than 500,000 shares (subject to adjustment for any stock dividend, stock split, stock combination or other similar transaction); and (c) the presentation by the Company at an appropriate medical conference of the “Overall Survival” data as defined in its ILLUMINATE-301 study protocol. ​ The Series B1/B2/B3/B4 Preferred Stock is non-voting and rank, as to payment upon the occurrence of any liquidation event, senior to the Company’s common stock. Shares of Series B1 Preferred Stock and Series B2 Preferred Stock are convertible, in whole or in part, at the option of the holder into fully paid and nonassessable shares of common stock at $1.52 per share, subject to adjustment. Shares of Series B3 Preferred Stock and Series B4 Preferred Stock are convertible, in whole or in part, at the option of the holder into fully paid and nonassessable shares of common stock at $1.82 per share, subject to adjustment. As more fully described in Note 7, the Company’s outstanding Series B1 Preferred Stock is classified in temporary equity, outside of stockholders’ equity as of December 31, 2020 and 2019. No shares of Series B2 Preferred Stock, Series B3 Preferred Stock or Series B4 Preferred Stock were outstanding as of December 31, 2020 and 2019. ​ Common Stock ​ Common Stock Authorized ​ On May 12, 2020, the Company’s stockholders approved the Charter Amendment. Also, on May 12, 2020, following stockholder approval, the Company filed the Charter Amendment with the Secretary of State of the State of Delaware ​ As of December 31, 2020, the Company had 140,000,000 shares of common stock authorized of which 35,750,149 shares of common stock were reserved for the issuance upon the exercise of outstanding warrants and options to purchase common stock, outstanding restricted stock units, the conversion of Series A and Series B1 convertible preferred stock, shares required to be reserved under the LPC Purchase Agreement (defined below), and shares available for grant under the Company’s 2013 Stock Incentive Plan and shares available for purchase under the Company’s 2017 Employee Stock Purchase Plan. ​ Put Shares ​ Pursuant to the terms of a unit purchase agreement dated as of May 5, 1998, the Company issued and sold a total of 149,960 shares of common stock (the “Put Shares”) at a price of $128.00 per share. Under the terms of the unit purchase agreement, the initial purchasers (the “Put Holders”) of the Put Shares have the right (the “Put Right”) to require the Company to repurchase the Put Shares. The Put Right may not be exercised by any Put Holder unless: (1) the Company liquidates, dissolves or winds up its affairs pursuant to applicable bankruptcy law, whether voluntarily or involuntarily; (2) all of the Company’s indebtedness and obligations, including without limitation the indebtedness under the Company’s then outstanding notes, has been paid in full; and (3) all rights of the holders of any series or class of capital stock ranking prior and senior to the common stock with respect to liquidation, including without limitation the Series A convertible preferred stock, have been satisfied in full. The Company may terminate the Put Right upon written notice to the Put Holders if the closing sales price of its common stock exceeds $256.00 per share for the twenty consecutive trading days prior to the date of notice of termination. Because the Put Right is not transferable, in the event that a Put Holder has transferred Put Shares since May 5, 1998, the Put Right with respect to those shares has terminated. As a consequence of the Put Right, in the event the Company is liquidated, holders of shares of common stock that do not have Put Rights with respect to such shares may receive smaller distributions per share upon the liquidation than if there were no Put Rights outstanding. ​ As of December 31, 2020, the Company has repurchased or received documentation of the transfer of 49,993 Put Shares and 4,472 of the Put Shares continued to be held in the name of Put Holders. The Company cannot determine at this time what portion of the Put Rights of the remaining 95,494 Put Shares have terminated. ​ Note 8. Stockholders’ Equity (Continued) ​ Equity Financings ​ April 2020 Private Placement ​ On April 7, 2020, the Company entered into a Securities Purchase Agreement (as amended to date, the “April 2020 Securities Purchase Agreement”) with Pillar Partners Foundation, L.P. (“Pillar Partners”), a related party as more fully described in Note 16, providing for the sale of securities in two closings exempt from the registration requirements of the Securities Act. Concurrent with the consummation of the April 2020 Securities Purchase Agreement, the Company issued and sold to Pillar Partners, for $5.0 million of aggregate consideration (the “April 2020 Private Placement First Closing”), (i) 3,039,514 shares of common stock and (ii) warrants to purchase 3,039,514 shares of the Company’s common stock with an exercise price of $2.28 per share. Each share and the accompanying common warrant sold in the April 2020 Private Placement First Closing had a combined purchase price of $1.645 , which included $0.125 for each share of common stock underlying each warrant. ​ On December 11, 2020, the Company entered into an amendment to the April 2020 Securities Purchase Agreement with Pillar Partners and Pillar Pharmaceuticals 6, L.P., a related party (“Pillar 6” and, collectively with Pillar Partners, the “April 2020 Purchasers”), principally to enable Pillar 6 to participate in the Second Closing (as defined below) pursuant to the April 2020 Purchase Agreement. Also on December 11, 2020, the Company issued and sold to the April 2020 Purchasers, for $5.0 million of aggregate consideration (the “April 2020 Private Placement Second Closing”), (i) 69,941 shares of the Company’s common stock, (ii) pre-funded warrants to purchase up to 2,677,311 shares of the Company’s common stock, at an exercise price of $0.01 per share, and (iii) warrants to purchase up to 1,373,626 shares of the Company’s common stock with an exercise price of $2.71 per share. Each share and the accompanying 0.5 common warrant sold in the April 2020 Private Placement Second Closing had a combined purchase price of $1.82 and each pre-funded warrant and the accompanying 0.5 common warrant had a combined purchase price of $1.81 . ​ Through December 31, 2020, net proceeds received pursuant to the April 2020 Securities Purchase Agreement, after deduction of offering expenses, was $9.8 million. All proceeds have been recorded within the Company’s statements of stockholders’ equity (deficit) as all securities issued pursuant to the April 2020 Securities Purchase Agreement were determined to be freestanding equity-classified instruments. ​ July 2020 Private Placement On July 13, 2020, the Company entered into a Securities Purchase Agreement (the “July 2020 Securities Purchase Agreement”) with Pillar Partners, Pillar 6, and Pillar Pharmaceuticals 7 L.P. (“Pillar 7”) (collectively, the “July 2020 Purchasers”), each a related party as more fully described in Note 16, under which the Company issued and sold to the July 2020 Purchasers in a private placement transaction exempt from the registration requirements of the Securities Act, for $5.1 million of aggregate consideration (the “July 2020 Private Placement First Closing”), (i) 749,993 shares of common stock, (ii) pre-funded warrants to purchase up to 2,014,234 shares of common stock, at an exercise price of $0.01 per share, and (iii) warrants to purchase 2,764,227 shares of the Company’s common stock with an exercise price of $2.58 per share. Each share (or pre-funded warrant) and the accompanying common warrant sold in the July 2020 Private Placement First Closing had a combined purchase price of $1.845 , which included $0.125 for each share of common stock underlying each accompanying warrant. ​ In addition, the Company has agreed to sell to the July 2020 Purchasers, at their option, pre-funded warrants to purchase up to 784,615 shares of the Company’s common stock, at an exercise price of $0.01 per share, and warrants to purchase up to 274,615 shares of the Company’s common stock, at an exercise price of $9.75 , for aggregate gross proceeds of $5.1 million (the “July 2020 Private Placement Second Closing”). Each pre-funded warrant and the 0.35 associated common warrant will have a combined purchase price of $6.50 ( $6.45625 per pre-funded warrant plus $0.04375 per 0.35 associated common warrant). The July 2020 Private Placement Second Closing can occur (at the option of the July 2020 Purchasers) on or before the tenth Business Day following the ORR Data Announcement (as defined in the July 2020 Securities Purchase Agreement) and will be held on or before the fifth day following delivery of written notice by the July 2020 Purchasers to the Company. ​ Note 8. Stockholders’ Equity (Continued) ​ Through December 31, 2020, net proceeds received pursuant to the July 2020 Securities Purchase Agreement, after deduction of offering expenses, was $5.0 million. All proceeds have been recorded within the Company’s statements of stockholders’ equity (deficit) as the securities issued pursuant to the July 2020 Securities Purchase Agreement, including the July 2020 Private Placement Second Closing option, were determined to be freestanding equity-classified instruments. ​ Common Stock Purchase Agreement On March 4, 2019, the Company entered into a Purchase Agreement with Lincoln Park Capital Fund, LLC (“Lincoln Park”), which was amended on September 2, 2020 (as amended to date, the “LPC Purchase Agreement”), pursuant to which, upon the terms and subject to the conditions and limitations set forth therein, Lincoln Park has committed to purchase an aggregate of $35.0 million of shares of Company common stock from time to time at the Company’s sole discretion over a 36-month period. As consideration for entering into the LPC Purchase Agreement, the Company issued 269,749 shares of Company common stock to Lincoln Park as a commitment fee (the “Commitment Shares”). The closing price of the Company’s common stock on March 4, 2019 was $2.84 and the Company did not receive any cash proceeds from the issuance of the Commitment Shares. ​ During the years ended December 31, 2020 and 2019, the Company sold 750,000 and 1,535,848 shares, respectively, pursuant to the LPC Purchase Agreement, resulting in net proceeds of $1.7 million and $3.7 million, respectively. As of December 31, 2020, the Company may sell up to an additional $29.5 million of shares under the LPC Purchase Agreement, subject to certain limitations. ​ "At-The-Market" Equity Program In November 2018, the Company entered into a Equity Distribution Agreement (the “ATM Agreement”) with JMP Securities LLC (“JMP”) pursuant to which the Company may issue and sell shares of its common stock having an aggregate offering price of up to $50.0 million (the “Shares”) through JMP as its agent. Subject to the terms and conditions of the ATM Agreement, JMP will use its commercially reasonable efforts to sell the Shares from time to time, based upon the Company’s instructions, by methods deemed to be an “at the market offering” as defined in Rule 415(a)(4) promulgated under the Securities Act of 1933, as amended, or if specified by the Company, by any other method permitted by law, including but not limited to in negotiated transactions. The Company has no obligation to sell any of the Shares, and the Company or JMP may at any time suspend sales under the ATM Agreement or terminate the ATM Agreement. JMP is entitled to a fixed commission of 3.0% of the gross proceeds from Shares sold. ​ During the years ended December 31, 2020 and 2019, the Company sold 3,608,713 and 532,700 Shares, respectively, pursuant to the ATM Agreement resulting in net proceeds, after deduction of commissions and other offering expenses, of $12.3 million and $1.6 million, respectively. No Shares were sold pursuant to the ATM Agreement during 2018. As of December 31, 2020, the Company may sell up to an additional $35.4 million of shares under the ATM Agreement. ​ ​ Note 8. Stockholders’ Equity (Continued) ​ Common Stock Warrants ​ In connection with various financing transactions, the Company has issued warrants to purchase shares of the Company’s common stock and preferred stock. The Company accounts for common stock and preferred stock warrants as equity instruments or liabilities, depending on the specific terms of the warrant agreement. See Note 2 for further details on accounting policies related to the Company’s warrants. ​ The following table summarizes outstanding warrants to purchase shares of the Company’s common stock and/or preferred stock as of December 31, 2020 and 2019: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of Shares ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ Weighted-Average ​ ​ ​ Description ​ 2020 ​ 2019 ​ Exercise Price ​ Expiration Date Liability-classified Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 2019 Series B1 warrants (1) ​ 2,368,400 ​ 2,368,400 ​ ​ $ 1.52 ​ Dec 2026 ​ ​ ​ 2,368,400 ​ 2,368,400 ​ ​ ​ ​ ​ ​ Equity-classified Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ May 2013 warrants 1,949,754 ​ 1,949,754 ​ ​ $ 0.08 ​ None ​ September 2013 warrants 514,756 ​ 514,756 ​ ​ $ 0.08 ​ None ​ February 2014 warrants 266,006 ​ 266,006 ​ ​ $ 0.08 ​ None ​ April 2020 Private Placement first closing warrants ​ 3,039,514 ​ — ​ ​ $ 2.28 ​ Apr 2023 ​ April 2020 Private Placement second closing warrants ​ 1,373,626 ​ — ​ ​ $ 2.71 ​ Dec 2023 ​ April 2020 Private Placement second closing warrants ​ 2,677,311 ​ — ​ ​ $ 0.01 ​ None ​ July 2020 Private Placement first closing warrants ​ 2,014,234 ​ — ​ ​ $ 0.01 ​ None ​ July 2020 Private Placement first closing warrants ​ 2,764,227 ​ — ​ ​ $ 2.58 ​ Jul 2023 ​ ​ ​ 14,599,428 ​ 2,730,516 ​ ​ ​ ​ ​ ​ Total outstanding 16,967,828 ​ 5,098,916 ​ ​ ​ ​ ​ ​ (1) The Series B1 warrants are exercisable for either common stock (exercise price of $1.52 ) or Series B1 Convertible Preferred Stock (exercise price of $152 ) at the discretion of the warrant holder. ​ The table below is a summary of the Company's warrant activity for the year ended December 31, 2020. ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Weighted-Average ​ ​ Warrants ​ Exercise Price Outstanding at December 31, 2019 5,098,916 ​ $ 0.75 Issued (1) 11,868,912 ​ 1.50 Exercised — ​ — Expired — ​ — Outstanding at December 31, 2020 16,967,828 ​ $ 1.28 (1) During th e year ended December 31, 2020, certain related parties were issued warrants as more fully described in Note 16.

Alliance Revenue

Alliance Revenue	12 Months Ended
	Dec. 31, 2020
Alliance Revenue
Alliance Revenue	Note 9. Alliance Revenue ​ Alliance revenue for the years ended December 31, 2020, 2019 and 2018 represents revenue from contracts with customers accounted for in accordance with ASC Topic 606. ​ For the year ended December 31, 2019, the Company recognized Alliance revenues totaling $1.4 million which consistent primarily of revenues recognized under the Licensee Agreement, as more fully described in Note 10, primarily related to the transfer of the IMO-8400 License and IMO-8400 drug product. For the year ended December 31, 2018, the Company recognized Alliance revenues totaling $0.7 million which consisted of (i) $0.5 million pursuant to the GSK Agreement, as more fully described in Note 10, and (ii) $0.2 million related to collaborations which have either been terminated and/or are not material to the Company’s current operations nor expected to be material in the future, including reimbursements by licensees of costs associated with research services and patent maintenance. ​ During the year ended December 31, 2018, the Company recognized Alliance revenues of $0.6 million as a result of changes in the contract liability balances associated with its contracts with customers. Such revenue recognized was included in the contract liability balance at the beginning of the period. See Note 10 for additional details regarding the Company’s collaboration arrangements.

Collaboration and License Agree

Collaboration and License Agreements	12 Months Ended
	Dec. 31, 2020
Collaboration and License Agreements
Collaboration and License Agreements	Note 10. Collaboration and License Agreements ​ Option and License Agreement with Licensee In April 2019, the Company entered into an amended and restated option and license agreement with a privately-held biopharmaceutical company (“Licensee”) , pursuant to which the Company granted Licensee (i) exclusive worldwide rights to develop and market IMO-8400 for the treatment, palliation and diagnosis of all diseases, conditions or indications in humans (the “IMO-8400 License”), (ii) an exclusive right and license to develop IMO-9200 in accordance with certain IMO-9200 pre-option exercise protocols (the “IMO-9200 Option Period License”), and (iii) an exclusive one-year option, exercisable at Licensee’s discretion, to obtain the exclusive worldwide rights to develop and market IMO-9200 for the treatment, palliation and diagnosis of all diseases, conditions or indications in humans (the “IMO-9200 Option”) (collectively, the “Licensee Agreement”). In connection with the Licensee Agreement, the Company transferred certain drug material to Licensee for Licensee’s use in development activities. Licensee is solely responsible for the development and commercialization of IMO-8400 and, if Licensee exercises the IMO-9200 Option, Licensee would be solely responsible for the development and commercialization of IMO-9200. ​ Under the terms of the Licensee Agreement, the Company received upfront, non-refundable fees totaling approximately $1.4 million and ownership of 10% of Licensee’s outstanding common stock, subject to future adjustment, for granting Licensee the IMO-8400 License, the IMO-9200 Option Period License and transfer of related drug materials. In addition, following expiry of the IMO-9200 Option in 2020, the Company is now only eligible to receive certain development and sales-based milestone payments and royalties on global net sales related to the IMO-8400 Compound and potential future IMO-8400 Products, each as defined in the Licensee Agreement. The Company does not anticipate the receipt of any of the future milestones or royalties in the short term, if ever. ​ The Company accounts for the Licensee Agreement in accordance with ASC 606. As of December 31, 2020, the total transaction price of the contract was $1.4 million, which excluded the Option Fee and all development and sales milestones as all such payments were fully constrained. Additionally, as of December 31, 2020, there were no remaining performance obligations under the Licensee Agreement. The Company re-evaluates its performance obligations and transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. ​ Note 10. Collaboration and License Agreements (Continued) ​ As disclosed above, in connection with the Licensee Agreement, the Company owns 10% of Licensee’s outstanding common stock, subject to future adjustment. The Company evaluated the guidance in ASC Topic 321, Investments-Equity Securities , and elected to account for the investment using the measurement alternative as the equity securities are without a readily determinable fair value, and the arrangement does not result in Idera having control or significant influence over Licensee. Accordingly, the securities are measured at cost, less any impairment, plus or minus changes resulting from observable price changes and are recorded in Other assets at a value of less than $0.1 million in the accompanying balance sheets. As of December 31, 2020, the Company considered the cost of the investment to not exceed the fair value of the investment and did not identify any observable price changes. Collaboration with GSK ​ In November 2015, the Company entered into a collaboration and license agreement with GSK to license, research, develop and commercialize pharmaceutical compounds from the Company’s nucleic acid chemistry technology for the treatment of selected targets in renal disease (the “GSK Agreement”). In connection with the GSK Agreement, GSK identified an initial target for the Company to attempt to identify a potential population of development candidates to address such target under a mutually agreed upon research plan. Prior to the wind-down of its discovery operations as more fully described in Note 10, the Company created multiple development candidates to address the initial target designated by GSK. Until November 2019, the expiration of the collaboration term, GSK had the right to designate one development candidate in its sole discretion, from the population of identified candidates, to move forward into clinical development. However, GSK did not designate any candidate for development during the collaboration term. If such designation had occurred, GSK would have been solely responsible for the development and commercialization activities of that designated development candidate. ​ The GSK Agreement also provided GSK with the option to select up to two additional targets at any time during the first two years of the GSK agreement, for further research under mutually agreed upon research plans. Upon selecting additional targets, GSK then had the option to designate one development candidate for each additional target, at which time GSK would have sole responsibility to develop and commercialize each such designated development candidate. GSK did not select any additional targets for research through expiry of the option period. ​ Under the terms of the GSK Agreement, the Company received a $2.5 million upfront, non-refundable, non-creditable cash payment upon the execution of the GSK Agreement. Additionally, the Company was initially eligible to receive a total of up to approximately $100 million in license, research, clinical development and commercialization milestone payments, of which $9 million of these milestone payments would have been payable by GSK upon the identification of the additional targets, the completion of current and future research plans and the designation of development candidates and $89 million would have been payable by GSK upon the achievement of clinical milestones and commercial milestones. As a result of GSK not designating a development candidate during the collaboration term, the Company is no longer eligible to receive any additional license, research, clinical development and commercialization milestone payments, or any royalty payments. ​ For the year ended December 31, 2018, the Company recognized Alliance revenues of $0.5 million pursuant to the GSK Agreement primarily related to the amortization of the $2.5 million upfront, non-refundable, non-creditable cash payment received upon the execution of the GSK Agreement, which was recognized as revenue on a straight-line basis over the estimated 36-month research plan period, which approximated the timing in which performance obligations were satisfied. No such revenues were recognized during 2020 or 2019.

Restructuring Costs

Restructuring Costs	12 Months Ended
	Dec. 31, 2020
Restructuring Costs
Restructuring Costs	Note 11. Restructuring Costs ​ In July 2018, the Company determined to wind-down its discovery operations, reduce the workforce in Cambridge, Massachusetts that supports such operations, and close its Cambridge facility (the “July 2018 Restructuring”). In connection with the reduction-in-workforce, 18 positions were eliminated, primarily in the area of discovery, representing approximately 40% of the Company’s employees. Of the 18 positions eliminated, 15 were effective July 31, 2018 with the remaining effective during the first half of 2019. The Company completed the consolidation of its operations to its Exton, Pennsylvania location in the third quarter of 2018. ​ Total restructuring-related charges incurred in connection with the July 2018 Restructuring was $3.3 million and comprised of (i) one-time termination costs in connection with the reduction in workforce, including severance, benefits and related costs, of approximately $2.8 million; (ii) contract termination costs of approximately $0.2 million in connection with the early lease termination for the Cambridge facility; and (iii) non-cash asset impairments of approximately $0.7 million, inclusive of $0.5 million of fixed asset impairments and $0.2 million in write-offs of facility-related prepaid expenses; offset by (iv) a non-cash gain of approximately $0.4 million related to the write-off of the remaining deferred rent liability associated with the Cambridge facility lease. ​ The following summarizes restructuring-related activity for the years ended December 31, 2020, 2019 and 2018: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ Employee Severance ​ Contract Termination Costs ​ Asset Impairments ​ Total Accrued restructuring balance as of December 31, 2017 $ — ​ $ — ​ $ — ​ $ — Charges incurred (1) ​ 2,635 ​ ​ 225 ​ ​ 674 ​ ​ 3,534 Cash payments ​ (1,380) ​ ​ (225) ​ ​ — ​ ​ (1,605) Non-cash settlements ​ (24) ​ ​ — ​ ​ (674) ​ ​ (698) Adjustments ​ ​ (84) ​ ​ — ​ ​ — ​ ​ (84) Accrued restructuring balance as of December 31, 2018 $ 1,147 ​ $ — ​ $ — ​ $ 1,147 Charges incurred ​ 181 ​ ​ — ​ ​ — ​ ​ 181 Cash payments ​ (1,215) ​ ​ — ​ ​ — ​ ​ (1,215) Accrued restructuring balance as of December 31, 2019 $ 113 ​ $ — $ — ​ $ 113 Charges incurred ​ — ​ ​ — ​ ​ — ​ ​ — Cash payments ​ (113) ​ ​ — ​ ​ — ​ ​ (113) Accrued restructuring balance as of December 31, 2020 $ — ​ $ — $ — ​ $ — (1) Excludes $0.4 million gain due to the write-off of the remaining deferred rent liability associated with the termination of the Cambridge, Massachusetts facility lease.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2020
Stock-Based Compensation
Stock-Based Compensation	Note 12. Stock-based Compensation ​ As of December 31, 2020, the only equity compensation plans from which the Company may currently issue new awards are the Company’s 2013 Stock Incentive Plan (as amended to date, the “2013 Plan”) and 2017 Employee Stock Purchase Plan (the “2017 ESPP”), each as more fully described below. ​ Equity Incentive and Employee Stock Purchase Plans ​ 2013 Stock Incentive Plan ​ The Company's board of directors adopted the 2013 Plan , which was approved by the Company’s stockholders effective July 26, 2013. Amendments to the 2013 Plan were approved by the Company’s stockholders in June 2014, June 2015, June 2017 and June 2019. The 2013 Plan is intended to further align the interests of the Company and its stockholders with its employees, including its officers, non-employee directors, consultants and advisers by providing equity-based incentives. T he 2013 Plan allows for the issuance of incentive stock options intended to qualify under Section 422 of the Internal Revenue Code, non-statutory stock options, stock appreciation rights, restricted stock awards, restricted stock units (“RSUs”), other stock-based awards and performance awards. The total number of shares of common stock authorized for issuance under the 2013 Plan is 5,653,057 shares of the Company’s common stock, plus such additional number of shares of common stock (up to 868,372 shares) as is equal to the number of shares of common stock subject to awards granted under the Company’s 2005 Stock Incentive Plan or 2008 Stock Incentive Plan (the “2008 Plan”), to the extent such awards expire, terminate or are otherwise surrendered, canceled, forfeited or repurchased by the Company at their original issuance price pursuant to a contractual repurchase right. ​ As of December 31, 2020, options to purchase a total of 4,034,540 shares of common stock and 903,321 RSUs were outstanding and up to 838,800 shares of common stock remained available for grant under the 2013 Plan. ​ Other Awards and Inducement Grants ​ The Company has not made any awards pursuant to other equity incentive plans, including the 2008 Plan, since the Company’s stockholders approved the 2013 Plan. As of December 31, 2020, options to purchase a total of 220,408 shares of common stock were outstanding under the 2008 Plan. In addition, as of December 31, 2020, non-statutory stock options to purchase an aggregate of 359,375 shares of common stock were outstanding that were issued outside of the 2013 Plan to certain employees in 2017, 2015 and 2014 pursuant to the Nasdaq inducement grant exception as a material component of new hires’ employment compensation. ​ 2017 Employee Stock Purchase Plan ​ The Company’s board of directors adopted the 2017 ESPP which was approved by the Company’s stockholders and became effective June 7, 2017. An amendment to the 2017 ESPP was approved by the Company’s stockholders in June 2019. The 2017 ESPP is intended to qualify as an "employee stock purchase plan" as defined in Section 423 of the Internal Revenue Code, and is intended to encourage our employees to become stockholders of ours, to stimulate increased interest in our affairs and success, to afford employees the opportunity to share in our earnings and growth and to promote systematic savings by them. The total number of shares of common stock authorized for issuance under the 2017 ESPP is 412,500 shares of common stock, subject to adjustment as described in the 2017 ESPP. Participation is limited to employees that would not own 5% or more of the total combined voting power or value of the stock of the Company after the grant. As of December 31, 2020, 245,342 shares remained available for issuance under the 2017 ESPP. ​ ​ Note 12. Stock-based Compensation (Continued) ​ Stock Purchase Plan Administration ​ The 2017 ESPP provides for offerings to employees to purchase common stock with offerings beginning on dates determined by the compensation committee of the board of directors or on the first business day thereafter. Each offering begins a “plan period” during which payroll deductions are to be made and held for the purchase of common stock at the end of the plan period. The compensation committee may, at its discretion, choose a plan period of 12 months or less for subsequent offerings and/or choose a different commencement date for offerings. During each plan period participating employees may elect to have a portion of their compensation, ranging from 1% to 10% of compensation as defined by the plan, withheld and used for the purchase of common stock at the end of each plan period. The purchase price is equal to 85% of the lower of the fair market value of a share of common stock on the first trading date of each plan period or the fair market value of a share of common stock on the last trading day of the plan period, and is limited by participant to $25,000 in fair value of common stock per year as well as other quarterly plan limitations as defined by each plan. ​ For the years ended December 31, 2020, 2019 and 2018, the Company issued 75,999 , 60,953 , and 24,824 shares of common stock, in each year respectively, under the 2017 ESPP and received proceeds of $0.1 million, $0.1 million and $0.2 million, in each year respectively, as a result of stock purchases. ​ Accounting for Stock-based Compensation ​ The Company recognizes non-cash compensation expense for stock-based awards under the Company’s equity incentive plans and employee stock purchases under the Company’s 2017 ESPP as follows: ● Stock Options: Compensation cost is recognized over an award’s requisite service period, or vesting period, using the straight-line attribution method, based on the grant date fair value determined using the Black-Scholes option-pricing model. ● RSUs: Compensation cost for time-based RSUs, which vest over time based only on continued service, is recognized on a straight-line basis over the requisite service period based on the fair value of the Company’s common stock on the date of grant. Compensation cost for awards that are subject to market considerations is recognized on a straight-line basis over the implied requisite service period, based on the grant date fair value estimated using a Monte Carlo simulation. Compensation cost for awards that are subject to performance conditions is recognized over the period of time commencing when the performance condition is deemed probable of achievement based on the fair value of the Company’s common stock on the date of grant. ● Employee Stock Purchases: Compensation cost is recognized over each plan period based on the fair value of the look-back provision, calculated using the Black-Scholes option-pricing model, considering the 15% discount on shares purchased. Total stock-based compensation expense attributable to stock-based payments made to employees and directors and employee stock purchases included in operating expenses in the Company's statements of operations for the years ended December 31, 2020, 2019 and 2018 was as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ 2020 2019 2018 Stock-based compensation: ​ ​ ​ ​ ​ ​ ​ Research and development ​ ​ ​ ​ ​ ​ ​ ​ ​ Employee Stock Purchase Plan ​ $ 88 $ 36 $ 71 Equity Incentive Plan ​ ​ 673 ​ 1,312 ​ 1,780 ​ ​ $ 761 $ 1,348 $ 1,851 General and administrative ​ ​ ​ ​ ​ ​ ​ ​ ​ Employee Stock Purchase Plan ​ $ 9 $ 20 $ 48 Equity Incentive Plan ​ ​ 2,871 ​ 2,477 ​ 3,751 ​ ​ $ 2,880 $ 2,497 $ 3,799 Restructuring costs ​ ​ ​ ​ ​ ​ ​ ​ ​ Equity Incentive Plan ​ $ — ​ $ — ​ $ 24 ​ ​ $ — ​ $ — ​ $ 24 Total stock-based compensation expense ​ $ 3,641 $ 3,845 $ 5,674 ​ Note 12. Stock-based Compensation (Continued) ​ During the years ended December 31, 2020, 2019 and 2018, the weighted average fair market value of stock options granted was $1.25 , $1.64 , and $7.00 , respectively. ​ Assumptions Used in Determining Fair Value of Stock Options ​ Inherent in the Black-Scholes option-pricing model are the following assumptions: Volatility . The Company estimates stock price volatility based on the Company’s historical stock price performance over a period of time that matches the expected term of the stock options. Risk-free interest rate . 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. Expected term . The expected term of stock options granted is based on an estimate of when options will be exercised or cancelled in the future. Dividend rate. The dividend rate is based on the historical rate, which the Company anticipates will remain at zero . Forfeitures . The Company accounts for forfeitures when they occur. Ultimately, the actual expense recognized over the vesting period will be for only those shares that vest. See Note 2. ​ The fair value of each option award at the date of grant was estimated using the Black-Scholes option pricing model. All options granted during the three years in the period ended December 31, 2020 were granted at exercise prices equal to the fair market value of the common stock on the dates of grant . ​ The following weighted average assumptions apply to the options to purchase 1,215,382 , 1,279,016 , and 1,136,874 shares of common stock granted to employees and directors during the years ended December 31, 2020, 2019 and 2018, respectively: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2019 ​ 2018 ​ Average risk-free interest rate ​ ​ 1.0% ​ ​ 2.1% ​ ​ 2.5% ​ Expected dividend yield ​ ​ — ​ ​ — ​ ​ — ​ Expected lives (years) ​ ​ 3.9 ​ ​ 3.7 ​ ​ 3.7 ​ Expected volatility ​ ​ 84% ​ ​ 84% ​ ​ 74% ​ Weighted average exercise price (per share) ​ $ 2.08 ​ $ 2.75 ​ $ 12.63 ​ ​ All options granted during the years ended December 31, 2020, 2019 and 2018 were granted at exercise prices equal to the fair market value of the common stock on the dates of grant . ​ Stock Option Activity ​ The following table summarizes stock option activity for the year ended December 31, 2020. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ($ in thousands, except per share data) ​ Stock ​ Weighted-Average ​ Weighted-Average ​ Aggregate Intrinsic Value Outstanding at December 31, 2019 4,220,417 ​ $ 13.08 6.6 ​ $ — ​ Granted 1,215,382 ​ 2.08 ​ ​ ​ ​ ​ ​ Exercised (5,265) ​ 2.84 ​ ​ ​ ​ ​ ​ Forfeited (206,323) ​ 6.12 ​ ​ ​ ​ ​ ​ Expired (609,888) ​ 18.61 ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2020 (1) 4,614,323 ​ $ 9.78 6.8 ​ $ 2,949 ​ Exercisable at December 31, 2020 2,490,179 ​ $ 15.12 5.2 ​ $ 455 ​ (1) Includes both vested stock options as well as unvested stock options for which the requisite service period has not been rendered but that are expected to vest based on achievement of a service condition. Note 12. Stock-based Compensation (Continued) ​ The fair value of options that vested during the year ended December 31, 2020 was $2.9 million. As of December 31, 2020, there was $3.5 million of unrecognized compensation cost related to unvested options, which the Company expects to recognize over a weighted average period of 2.2 years. ​ Restricted Stock Activity The following table summarizes restricted stock activity for the year ended December 31, 2020: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Time-based Awards ​ Market/Performance-based Awards ($ in thousands, except per share data) ​ Number of Shares ​ Weighted-Average ​ Number of Shares ​ Weighted-Average Nonvested shares at December 31, 2019 193,625 ​ $ 3.14 ​ — ​ $ — Granted 365,845 ​ 2.65 ​ 556,888 ​ 1.54 Cancelled (28,895) ​ 2.75 ​ (7,570) ​ 1.54 Vested (176,572) ​ 3.95 ​ — ​ — Nonvested shares at December 31, 2020 354,003 ​ $ 2.27 ​ 549,318 ​ $ 1.54 ​ Time-based Restricted Stock Units ​ In December 2020, the Company’s Chief Executive Officer was granted an award of 128,170 RSUs, pursuant to the 2013 Plan, in lieu of salary pursuant to a January 10, 2020 amendment to the officers’ employment agreement. The RSUs were fully vested on the grant date. ​ As of December 31, 2020, there was $0.7 million of unrecognized compensation cost related to the Company’s time-based RSUs, which is expected to be recognized over a weighted average period of 1.9 years. ​ Market/Performance-based Restricted Stock Units ​ In July 2020, the Company granted RSUs to certain employees, including executive officers, under the 2013 Plan, with vesting that may occur upon a combination of specific performance and/or market conditions. Accordingly, the Company views these RSUs as two separate awards: (i) an award that vests if the market condition is achieved, and (ii) an award that vests whether or not the market condition is achieved, so long as the performance condition is achieved. The Company is currently recognizing compensation expense for these awards over the estimated requisite service period of 2.36 years based on the estimated fair value when considering the market condition of the award, which was determined using a Monte Carlo simulation. During the year ended December 31, 2020, the Company recognized $0.2 million of compensation expense related to these awards. As of December 31, 2020, the remaining unrecognized compensation cost for the market-based component of these awards, which is expected to be recognized over a weighted-average period of 1.5 years, is $0.7 million. In addition, should the performance condition be achieved, the Company would recognize an additional $0.3 million of compensation expense.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies
Commitments and Contingencies	Note 13. Commitments and Contingencies ​ Lease Commitments ​ As of December 31, 2020, the Company’s leased assets primarily consisted of its office headquarters in Exton, Pennsylvania. Prior to the September 30, 2018 termination date, the Company also leased a facility in Cambridge, Massachusetts. During 2020, 2019 and 2018, rent expense, including real estate taxes, was $0.4 million, $0.3 million, and $1.7 million, respectively. The leases are classified as operating leases. ​ Future minimum commitments as of December 31, 2020 under the Company’s lease agreements are approximately: ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ Operating Leases (in thousands) 2021 ​ 244 ​ 2022 ​ ​ 249 ​ 2023 ​ ​ 250 ​ 2024 ​ ​ 240 ​ 2025 ​ 101 ​ ​ ​ $ 1,084 ​ ​ The Company entered into the Exton, Pennsylvania facility lease on April 1, 2015, which was subsequently amended on September 23, 2015 to include additional space. The Company currently leases approximately 11,000 square feet of office space at our Exton facility. The lease expires on May 31, 2025. ​ Vendor Financing Arrangement ​ In October 2020, the Company entered into a short-term financing arrangement with a third-party vendor to finance insurance premiums. As of December 31, 2020, the balance of $0.4 million, is scheduled to be paid in monthly installments through June 2020.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Taxes
Income Taxes	Note 14. Income Taxes ​ As of December 31, 2020, the Company had cumulative federal and state net operating loss carryforwards (“NOLs”) of approximately $328.7 million and $323.2 million available to reduce federal and state taxable income, respectively. As a result of the Tax Cuts and Jobs Act of 2017, federal net operating losses incurred for taxable years beginning after January 1, 2018 have an unlimited carryforward period, but can only be utilized to offset 80% of taxable income in future taxable periods. Of the $328.7 million of federal NOLs, $131.3 million have an unlimited carryforward and the remaining NOLs are still subject to expiration through 2037. State NOLs are still subject to expiration according to the laws of each respective jurisdiction. The Company files state tax returns in Massachusetts and Pennsylvania whereby both jurisdictions impose a 20-year carryforward period. All $323.2 million of state NOLs expire through 2040, with the first year of expiration being 2032 for $23.4 million of Massachusetts NOLs. In addition, at December 31, 2020, the Company had cumulative federal and state tax credit carryforwards of $25.0 million and $1.9 million, respectively, available to reduce federal and state income taxes, respectively, which expire through 2040 and 2033, respectively, for federal and state purposes, other than those that have an unlimited carryforward period. ​ Sections 382 and 383 of the Internal Revenue Code prescribe limitations on the amount of NOLs and tax credit carryforwards that may be utilized in any one year. The Company has completed several financings since the effective date of the Tax Reform Act of 1986, which as of December 31, 2020, have resulted in ownership changes that will significantly limit the Company’s ability to utilize its net operating loss and tax credit carryforwards. In December 2017, the Company completed a study which determined that ownership changes had occurred. The federal and state net operating loss and tax credit carryforwards and related deferred tax assets shown in the table below have been adjusted to reflect the limitations that resulted from this study. As no study has been completed subsequent to 2017, additional ownership change limitations may result from ownership changes that have occurred, or may occur in the future. The Company continues to monitor equity activity and potential ownership changes. Note 14. Income Taxes (Continued) ​ As of December 31, 2020 and 2019, the components of the deferred tax assets are approximately as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ 2020 2019 Operating loss carryforwards ​ $ 90,895 ​ $ 81,403 ​ Tax credit carryforwards ​ 26,550 ​ 23,072 ​ Stock-based compensation ​ ​ 6,820 ​ ​ 7,818 ​ Lease liabilities ​ ​ 276 ​ ​ 308 ​ Other ​ 162 ​ 176 ​ Total deferred tax assets ​ 124,703 ​ 112,777 ​ Right-of-use asset ​ ​ (270) ​ ​ (306) ​ Valuation allowance ​ (124,433) ​ (112,471) ​ Net deferred tax assets ​ $ — ​ $ — ​ ​ ​ The Company has provided a full valuation allowance for its deferred tax asset due to the uncertainty surrounding the ability to realize these assets. ​ The difference between the U.S. federal corporate tax rate and the Company’s effective tax rate for the years ended December 31, 2020, 2019 and 2018 is as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2019 ​ 2018 Expected federal income tax rate (21.0) % ​ (21.0) % ​ (21.0) % Expiring credits and NOLs — ​ ​ — ​ ​ 1.0 ​ Change in valuation allowance 10.6 ​ ​ 26.2 ​ ​ 37.9 ​ Federal and state credits (3.1) ​ ​ (8.1) ​ ​ (7.4) ​ State income taxes, net of federal benefit (1.9) ​ ​ (4.7) ​ ​ (9.7) ​ Warrant and future tranche right revaluation loss ​ 14.2 ​ ​ 4.3 ​ ​ — ​ Stock-based compensation 0.2 ​ ​ 0.5 ​ ​ 0.5 ​ Other 1.0 ​ ​ 2.8 ​ ​ (1.3) ​ Effective tax rate 0.0 % ​ 0.0 % ​ 0.0 % ​ The Company applies ASC 740-10, Accounting for Uncertainty in Income Taxes, an interpretation of ASC 740 . ASC 740-10 clarifies the accounting for uncertainty in income taxes recognized in financial statements and requires the impact of a tax position to be recognized in the financial statements if that position is more likely than not of being sustained by the taxing authority. The Company had no unrecognized tax benefits resulting from uncertain tax positions at December 31, 2020 and 2019. ​ The Company has not conducted a study of its research and development tax credit carryforwards. Such a study might result in an adjustment to the Company’s research and development credit carryforwards, however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position under ASC 740-10. A full valuation allowance has been provided against the Company’s research and development credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the statements of operations if an adjustment was required. ​ The Company files income tax returns in the U.S. federal, Massachusetts and Pennsylvania jurisdictions. The Company is no longer subject to tax examinations for years before 2017, except to the extent that it utilizes tax attributes that originated before 2017. The Company does not believe there will be any material changes in its unrecognized tax positions over the next 12 months . The Company has not incurred any interest or penalties. In the event that the Company is assessed interest or penalties at some point in the future, they will be classified in the statements of operations as general and administrative expense.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2020
Employee Benefit Plan
Employee Benefit Plan	Note 15. Employee Benefit Plan ​ The Company has an employee benefit plan under Section 401(k) of the Internal Revenue Code. The plan allows employees to make contributions up to a specified percentage of their compensation. Under the plan, the Company matches a portion of the employees’ contributions up to a defined maximum. Prior to August 2018, the Company historically contributed up to 3% of employee base salary, by matching 50% of the first 6% of annual base salary contributed by each employee. Effective August 2018, the Company began contributing up to 5% of employee base salary, by matching 100% of the first 5% of annual base salary contributed by each employee. Approximately $0.3 million, $0.3 million and $0.2 million of 401(k) benefits were charged to operating expenses for the years ended December 31, 2020, 2019 and 2018, respectively. ​

Related Party Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2020
Related Party Transactions
Related Party Transactions	Note 16. Related Party Transactions ​ Baker Brothers ​ Julian C. Baker, a member of the Company’s Board until his resignation in September 2018, is a principal of Baker Bros. Advisors, LP. Additionally, Kelvin M. Neu, a member of Company’s Board until his resignation in June 2019, is an employee of Baker Bros. Advisors, LP. As of December 31, 2020, Baker Bros. Advisors, LP and certain of its affiliated funds (collectively, “Baker Brothers”) held sole voting power with respect to an aggregate of 4,608,786 shares of the Company’s common stock, representing approximately 12% of the Company's outstanding common stock. ​ During 2019, Baker Brothers purchased shares of the Company’s Series B1 Preferred Stock and accompanying warrants to purchase common stock in connection with the December 2019 Private Placement, as more fully described in Note 7. Concurrent with the December 2019 Private Placement, the Company amended the warrants initially issued to Baker Brothers and other holders on May 7, 2013, September 30, 2013 and February 10, 2014 to remove expiration date. Under the terms of the warrants issued to Baker Brothers and the December 2019 Securities Purchase Agreement related to the securities issued in connection with the 2019 Private Placement, Baker Brothers is not permitted to convert or exercise any common stock equivalents to the extent that such conversion or exercise would result in Baker Brothers (and its affiliates) beneficially owning more than 4.99% of the number of shares of our common stock outstanding immediately after giving effect to the issuance of shares of common stock issuable upon conversion or exercise of such securities. Baker Brothers has the right to increase this beneficial ownership limitation in its discretion on 61 days ' prior written notice to us, provided that in no event is Baker Brothers permitted to convert or exercise such securities to the extent that such exercise would result in Baker Brothers (and its affiliates) beneficially owning more than 19.99% of the number of shares of our common stock outstanding immediately after giving effect to the issuance of shares of common stock issuable upon conversion or exercise of such securities. ​ During 2018, Baker Brothers exercised warrants to purchase 2,700,791 shares of the Company’s common stock at an exercise price of $3.76 per share for a total exercise price of approximately $9.5 million. ​ As of December 31, 2020, Baker Brothers held warrants to purchase up to 2,708,812 shares of the Company’s common stock at an exercise price of $0.08 per share, warrants to purchase up to 2,368,400 shares of the Company’s common stock (or, if Baker Brothers elects to exercise the warrants for shares of Series B1 Preferred Stock, 23,684 shares of Series B1 Preferred Stock), at an exercise price of $1.52 per share (or, if Baker Brothers elects to exercise the warrants for shares of Series B1 Preferred Stock, $152 per Series B1 Preferred Warrant Share). ​ Pillar Investment Entities ​ Youssef El Zein, a member of the Company’s board of directors until his resignation in October 2017, is a director and controlling stockholder of Pillar Invest Corporation (“Pillar Invest”), which is the general partner of Pillar Pharmaceuticals I, L.P., Pillar Pharmaceuticals II, L.P., Pillar Pharmaceuticals III, L.P., Pillar Pharmaceuticals IV, L.P., Pillar Pharmaceuticals V, L.P., Pillar 6 and Pillar Partners (collectively, the “Pillar Investment Entities”). As of December 31, 2020, the Pillar Investment Entities own approximately 18% of the Company's common stock. ​ ​ Note 16. Related Party Transactions (Continued) ​ During 2020, the Company sold shares of its common stock, prefunded warrants and common stock warrants to entities affiliated with Pillar Invest Corporation in connection with private placement transactions, as more fully descried in Note 8. ​ During 2018, Participations Besancon , an investment fund advised by Pillar Invest having no affiliation with Mr. El Zein, exercised warrants to purchase 150,000 shares of the Company’s common stock at an exercise price of $3.76 per share for a total exercise price of approximately $0.6 million. ​ As of December 31, 2020, the Pillar Investment Entities held (i) warrants to purchase up to 3,039,514 shares of the Company’s common stock at an exercise price of $2.28 per share, (ii) warrants to purchase up to 2,764,227 shares of the Company’s common stock at an exercise price of $2.58 per share, (iii) prefunded warrants to purchase up to 2,014,234 shares of the Company’s common stock at an exercise price of $0.01 per share, (iv) warrants to purchase up to 1,373,626 shares of the Company’s common stock at an exercise price of $2.71 per share, and (v) prefunded warrants to purchase up to 2,677,311 shares of the Company’s common stock at an exercise price of $0.01 per share. Additionally, Pillar held options to purchase Company securities in the April 2020 Private Placement Second Closing and July 2020 Private Placement Second Closing, as more fully described in Note 8. ​ Subsequent to December 31, 2020, in January 2020, Pillar 6 exercised prefunded warrants to purchase 643,525 shares of the Company’s common stock at an exercise price of $0.01 per share. ​ Board Fees Paid in Stock ​ Pursuant to the Company’s director compensation program, in lieu of director board and committee fees of $0.3 million, $0.1 million, and $0.1 million, respectively, incurred during each of the years ended December 31, 2020, 2019 and 2018, respectively, the Company issued 145,392 , 53,985 , and 13,654 shares of common stock, respectively, to certain of its directors. Director board and committee fees are paid in arrears and the number of shares issued was calculated based on the market closing price of the Company’s common stock on the issuance date. ​ Officer Salary Paid in Stock ​ In December 2020, the Company’s Chief Executive Officer was granted an award of 128,170 RSUs, pursuant to the 2013 Plan, in lieu of salary of $0.6 million pursuant to a January 10, 2020 amendment to the officers’ employment agreement. The RSUs were fully vested on the grant date. ​

Net Loss per Common Share Appli

Net Loss per Common Share Applicable to Common Stockholders	12 Months Ended
	Dec. 31, 2020
Net Loss per Common Share Applicable to Common Stockholders
Net Loss per Common Share Applicable to Common Stockholders	Note 17. Net Loss per Common Share Applicable to Common Stockholders ​ Net loss applicable to common stockholders represents net loss adjusted for deemed dividends related to the December 2019 Private Placement, as more fully described in Note 7. ​ The Company uses the two-class method to compute net income (loss) per common share during periods the Company realizes net income and has securities outstanding (e.g. redeemable convertible preferred stock) that entitle the holder to participate in dividends and earnings of the Company. In addition, the Company analyzes the potential dilutive effect of outstanding redeemable convertible preferred stock under the "if-converted" method when calculating diluted earnings per share and reports the more dilutive of the approaches (two class or "if-converted"). The two-class method is not applicable during periods with a net loss, as the holders of the redeemable convertible preferred stock have no obligation to fund losses. For all periods presented, the two-class method was not applicable. The Company also analyzes the potential dilutive effect of outstanding stock options, unvested restricted stock units, warrants and shares underlying future tranche rights under the treasury stock method (as applicable), during periods of income, or during periods in which income is recognized related to changes in fair value of its liability-classified securities. ​ For the years ended December 31, 2020, 2019 and 2018, diluted net loss per common share applicable to common stockholders was the same as basic net loss per common share applicable to common stockholders as the effects of the Company’s potential common stock equivalents are antidilutive. Potentially dilutive securities, whose effect would have been antidilutive, were excluded from the computation of diluted earnings per share for each of the years ended December 31, 2020, 2019 and 2018. ​ T otal antidilutive securities excluded from the calculation of diluted net loss per share for the years ended December 31, 2020, 2019 and 2018, were as follows: ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ 2020 ​ ​ 2019 ​ 2018 Stock options ​ 4,614 ​ ​ 4,220 ​ 3,305 Restricted stock units ​ 903 ​ ​ 194 ​ — Common stock warrants ​ 16,968 ​ ​ 5,099 ​ 2,769 Convertible preferred stock ​ 2,369 ​ ​ 2,369 ​ 1 Future tranche rights ​ 50,467 ​ ​ 49,407 ​ — Total ​ 75,321 ​ ​ 61,289 ​ 6,075 ​ ​

Subsequent Events

Subsequent Events	12 Months Ended
	Dec. 31, 2020
Subsequent Events
Subsequent Events	Note 18. Subsequent Events ​ The Company considers events or transactions that occur after the balance sheet date but prior to the issuance of the financial statements to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. ​ Proceeds from Sale of Common Stock ​ "At-The-Market" Equity Program ​ During the period January 1, 2021 through February 28, 2021, the Company sold 2,394,956 shares of its common stock pursuant to the ATM Agreement, as more fully described in Note 8, resulting in net proceeds, after deduction of commissions , of $12.1 million. As of February 28, 2021, the Company may sell up to an additional $22.9 million of shares under the ATM Agreement. ​ Common Stock Purchase Agreement ​ During the period January 1, 2020 through February 28, 2021, the Company sold 800,000 shares of its common stock pursuant to the LPC Purchase Agreement, as more fully described in Note 8, resulting in net proceeds of $4.2 million. As of February 28, 2021, the Company may sell up to an additional $25.3 million of shares under the LPC Purchase Agreement. ​

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation ​ The accompanying financial statements have been prepared in accordance with U.S. generally accepted accounting principles (“GAAP”).
Use of Estimates	Use of Estimates ​ The preparation of financial statements in conformity with GAAP requires management to make estimates, judgements, and assumptions that affect the reported amounts of assets, liabilities, equity, revenues and expenses, and related disclosure of contingencies in the accompanying financial statements and these notes. In addition, management’s assessment of the Company’s ability to continue as a going concern involves the estimation of the amount and timing of future cash inflows and outflows. On an ongoing basis, the Company evaluates its estimates, judgments and methodologies. The Company bases its estimates on historical experience and on various other assumptions that are believed to be reasonable. Actual results could differ materially from those estimates.
Segment Information	Segment Information ​ Operating segments are defined as components of an enterprise in 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 assessing performance. The Company views its operations and manages its business as one operating segment, which is the business of developing novel therapeutics for oncology and rare diseases.
Financial Instruments	Financial Instruments ​ The fair value of the Company’s financial instruments is determined and disclosed in accordance with the three-tier fair value hierarchy specified in Note 3. The Company is required to disclose the estimated fair values of its financial instruments. As of December 31, 2020 and 2019, the Company’s financial instruments consisted of cash, cash equivalents, short-term investments, receivables, and warrant and future tranche right liabilities. The estimated fair values of these financial instruments approximate their carrying values as of December 31, 2020 and 2019. As of December 31, 2020, the Company did not have any other derivatives, hedging instruments or other similar financial instruments.
Concentration of Credit Risk	Concentration of Credit Risk ​ Financial instruments that subject the Company to credit risk primarily consist of cash, cash equivalents and short-term investments. The Company’s credit risk is managed by investing in highly rated money market instruments, U.S. treasury bills, corporate bonds, commercial paper and/or other debt securities. Due to these factors, no significant additional credit risk is believed by management to be inherent in the Company’s assets. As of December 31, 2020, all of the Company’s cash and cash equivalents were held at two financial institutions. ​
Cash and Cash Equivalents	Cash and Cash Equivalents ​ The Company considers all highly liquid investments with maturities of 90 days or less when purchased to be “cash equivalents.” Cash and cash equivalents at December 31, 2020 and 2019 consisted of cash and money market funds.
Property and Equipment	Property and Equipment ​ Property and equipment is carried at acquisition cost less accumulated depreciation, subject to review for impairment whenever events or changes in circumstances indicate that the carrying amount of the asset may not be recoverable as described further under the heading "Impairment of Long-Lived Assets" below. The cost of normal, recurring, or periodic repairs and maintenance activities related to property and equipment are expensed as incurred. The cost for planned major maintenance activities, including the related acquisition or construction of assets, is capitalized if the repair will result in future economic benefits. ​ Depreciation and amortization are computed using the straight-line method based on the estimated useful lives of the related assets. Leasehold improvements are amortized over the remaining lease term or the related useful life, if shorter. Equipment and other long-lived assets are depreciated over three to five years . ​ When an asset is disposed of, the associated cost and accumulated depreciation is removed from the related accounts on the Company's balance sheet with any resulting gain or loss included in the Company's statement of operations.
Operating Lease Right-of-use Asset and Lease Liability	Operating Lease Right-of-use Asset and Lease Liability ​ The Company accounts for leases under ASC Topic 842, Leases . Operating leases are included in “Operating lease right-of-use assets” within the Company’s balance sheets and represent the Company’s right to use an underlying asset for the lease term. The Company’s related obligation to make lease payments are included in “Operating lease liability” and “Operating lease liability, net of current portion” within the Company’s balance sheets. Operating lease right-of-use (“ROU”) assets and liabilities are recognized at commencement date based on the present value of lease payments over the lease term. As most of the Company’s leases do not provide an implicit rate, the Company uses 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. Lease expense for lease payments is recognized on a straight-line basis over the lease term. The ROU assets are tested for impairment according to ASC Topic 360, Property, Plant, and Equipment (“ASC 360”). Leases with an initial term of 12 months or less are not recorded on the balance sheet and are recognized as lease expense on a straight-line basis over the lease term. ​ As of December 31, 2020 and 2019, the Company’s operating lease ROU assets and corresponding short-term and long-term lease liabilities primarily relate to its existing Exton, PA facility operating lease which expires on May 31, 2025.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets ​ In accordance with ASC 360-10-35, Impairment or Disposal of Long-Lived Assets , the Company reviews its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable (i.e. impaired). Once an impairment is determined, the actual impairment recognized is the difference between the carrying amount and the fair value (less costs to sell for assets to be disposed of) as estimated using one of the following approaches: income, cost and/or market. Fair value using the income approach is determined primarily using a discounted cash flow model that uses the estimated cash flows associated with the asset or asset group under review, discounted at a rate commensurate with the risk involved. Fair value utilizing the cost approach is determined based on the replacement cost of the asset reduced for, among other things, depreciation and obsolescence. Fair value, utilizing the market approach, benchmarks the fair value against the carrying amount.
Other Current Liability	Other Current Liability ​ In October 2020, the Company entered into a short-term financing arrangement with a third-party vendor to finance insurance premiums. The aggregate amount financed under this agreement was $0.6 million. As of December 31, 2020, the balance of $0.4 million, which is included in “Other current liability’ in the Company’s balance sheets, is scheduled to be paid in monthly installments through June 2021.
Warrant Liability	Warrant Liability ​ The Company accounts for stock warrants as either equity instruments, liabilities or derivative liabilities in accordance with ASC 480, Distinguishing Liabilities from Equity (“ASC 480”) and/or ASC 815, Derivatives and Hedging (“ASC 815”), depending on the specific terms of the warrant agreement. Freestanding warrants for shares that are potentially redeemable, whereby the Company may be required to transfer assets (e.g. cash or other assets) outside of its control, are classified as liabilities. Liability-classified warrants are recorded at their estimated fair values at each reporting period until they are exercised, terminated, reclassified or otherwise settled. Changes in the estimated fair value of liability-classified warrants are recorded in Warrant Revaluation (Loss) Gain in the Company’s statements of operations. Equity classified warrants are recorded within additional paid-in capital at the time of issuance and not subject to remeasurement. For additional discussion on warrants, see Note 8.
Future Tranche Right Liability	Future Tranche Right Liability ​ On December 23, 2019, the Company entered into a Securities Purchase Agreement (the “December 2019 Securities Purchase Agreement”) with institutional investors affiliated with Baker Brothers (the “Purchasers”), an existing stockholder and related party (see Note 16). As more fully described in Note 7, the December 2019 Securities Purchase Agreement contains call options on redeemable preferred shares with warrants (conditionally exercisable for shares that are puttable). The Company determined that these call options represent freestanding financial instruments and accounts for the options as liabilities (“Future Tranche Right Liability”) under ASC 480, which requires the measurement and recognition of the fair value of the liability at the time of issuance and at each reporting period. Any change in fair value is recognized in Future Tranche Right Liability Revaluation (Loss) Gain in the Company’s statements of operations. ​ As of December 31, 2020, the Future Tranche Right Liability is classified as a long-term liability in the Company’s balance sheet as settlement is in the form of the applicable Series B convertible preferred stock and warrants exercisable for shares of either Series B1 Preferred Stock or the Company’s common stock. As of December 31, 2019, the Future Tranche Right Liability was classified as a current liability because the Future Tranche Rights and related Option Fee, each defined in Note 7, were subject to the Company obtaining required shareholder approval, which was obtained in May 2020. ​
Preferred Stock	Preferred Stock ​ The Company applies ASC 480 when determining the classification and measurement of its preferred stock. Preferred shares subject to mandatory redemption are classified as liability instruments and are measured at fair value. Conditionally redeemable preferred shares (including preferred shares that feature redemption rights that are either within the control of the holder or subject to redemption upon the occurrence of uncertain events not solely within the Company’s control) are classified as temporary equity. At all other times, preferred shares are classified as stockholders’ equity. ​ Accretion of redeemable convertible preferred stock includes the accretion of the Company's Series B redeemable convertible preferred stock to its stated value. The carrying value of the Series B redeemable convertible preferred stock is being accreted to redemption value using the effective interest method, from the date of issuance to the earliest date the holders can demand redemption.
Redeemable Preferred Stock Issued with Other Freestanding Instruments	Redeemable Preferred Stock Issued with Other Freestanding Instruments ​ The Company considers guidance within ASC 470-20, Debt (ASC 470), ASC 480, and ASC 815 when accounting for a redeemable equity instrument issued with other freestanding instruments (e.g. detachable warrants and future tranche right liabilities), such as in the December 2019 Private Placement (Note 7). In circumstances in which redeemable convertible preferred stock is issued with freestanding liability-classified instruments, the proceeds from the issuance of the convertible preferred stock are first allocated to those instruments at their full estimated fair value. The remaining proceeds, as further reduced by discounts created by the bifurcation of embedded derivatives and/or beneficial conversion features, if any, are allocated to the redeemable equity instrument.
Revenue Recognition	Revenue Recognition ​ The Company recognizes revenue in accordance with ASC Topic 606, Revenue from Contracts with Customers (“ASC 606’), which applies to all contracts with customers, except for contracts that are within the scope of other standards, such as leases, insurance, collaboration arrangements and financial instruments. In accordance with ASC 606, the Company 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 revenue recognition for arrangements that the Company determines are within the scope of ASC Topic 606, it performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the entity satisfies a performance obligation. ​ The Company only applies the five-step model to contracts when it determines that it is probable it will collect the consideration to which it is entitled 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. ​ Amounts received prior to satisfying the revenue recognition criteria are recognized as deferred revenue in the Company’s balance sheet. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as current portion of deferred revenue. 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. ​ Alliance Revenues The Company’s revenues have primarily been generated through collaborative research, development and/or commercialization agreements. The terms of these agreements may include payment to the Company of one or more of the following: nonrefundable, up-front license fees; research, development and commercial milestone payments; and other contingent payments due based on the activities of the counterparty or the reimbursement by licensees of costs associated with patent maintenance. Each of these types of revenue are recorded as Alliance revenues in the Company’s statements of operations. 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. ​ ​ Note 2. Summary of Significant Accounting Policies (Continued) ​ See Note 10, “Collaboration and License Agreements” for additional details regarding the Company’s collaboration and out-licensing arrangements. As part of the accounting for these arrangements, the Company allocates the transaction price to each performance obligation on a relative stand-alone selling price basis. The stand-alone selling price may be, but is not presumed to be, the contract price. In determining the allocation, the Company maximizes the use of observable inputs. When the stand-alone selling price of a good or service is not directly observable, the Company estimates the stand-alone selling price for each performance obligation using assumptions that require judgment. Acceptable estimation methods include, but are not limited to: (i) the adjusted market assessment approach, (ii) the expected cost plus margin approach, and (iii) the residual approach (when the stand-alone selling price is not directly observable and is either highly variable or uncertain). In order for the residual approach to be used, the Company must demonstrate that (a) there are observable stand-alone selling prices for one or more of the performance obligations and (b) one of the two criteria in ASC 606-10-32-34(c)(1) and (2) is met. The residual approach cannot be used if it would result in a stand-alone selling price of zero for a performance obligation as a performance obligation, by definition, has value on a stand-alone basis. ​ An option in a contract to acquire additional goods or services gives rise to a performance obligation only if the option provides a material right to the customer that it would not receive without entering into that contract. Factors that the Company considers in evaluating whether an option represents a material right include, but are not limited to: (i) the overall objective of the arrangement, (ii) the benefit the collaborator might obtain from the arrangement without exercising the option, (iii) the cost to exercise the option (e.g. priced at a significant and incremental discount) and (iv) the likelihood that the option will be exercised. With respect to options determined to be performance obligations, the Company recognizes revenue when those future goods or services are transferred or when the options expire. ​ The Company’s revenue arrangements may include the following: Up-front License Fees: If a license is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenues from nonrefundable, up-front fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled 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 from non-refundable, up-front fees. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments: At the inception of an agreement that includes research and development milestone payments, the Company evaluates whether each milestone is 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 transaction price is then 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. At the end of each subsequent reporting period, the Company re-evaluates the probability of achievement of such milestones and any related 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 Alliance revenues and earnings in the period of adjustment. Research and Development Activities: If the Company is entitled to reimbursement from its collaborators for specified research and development activities or the reimbursement of costs associated with patent maintenance, the Company determines whether such funding would result in Alliance revenues or an offset to research and development expenses. Reimbursement of patent maintenance costs are recognized during the period in which the related expenses are incurred as Alliance revenues in the Company’s statements of operations. ​ Note 2. Summary of Significant Accounting Policies (Continued) ​ Royalties: If the Company is entitled to receive sales-based royalties from its collaborator, including milestone payments based on the 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, provided the reported sales are reliably measurable, 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 collaboration and license arrangements. Manufacturing Supply and Research Services: Arrangements that include a promise for future supply of drug substance, drug product or research services at the licensee’s discretion are generally considered as options. The Company assesses if these options provide a material right to the licensee and if so, they are accounted for as separate performance obligations. If the Company is entitled to additional payments when the licensee exercises these options, any additional payments are recorded in Alliance revenues when the licensee obtains control of the goods, which is upon delivery, or as the services are performed. The Company receives payments from its licensees based on schedules established in each contract. Upfront payments and fees are recorded as deferred revenue upon receipt, and may require deferral of revenue recognition to a future period until the Company performs its obligations under these arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the licensees and the transfer of the promised goods or services to the licensees will be one year or less.
Research and Development Expenses	Research and Development Expenses ​ All research and development expenses are expensed as incurred. Research and development expenses are comprised of costs incurred in performing research and development activities, including drug development trials and studies, drug manufacturing, laboratory supplies, external research, payroll including stock-based compensation and overhead. Nonrefundable advance payments for goods or services to be received in the future for use in research and development activities are deferred and capitalized. The capitalized amounts are expensed as the related goods are accepted by the Company or the services are performed. As of December 31, 2020 and 2019, the Company recorded approximately $2.5 million and $2.8 million as prepaid research and development, respectively, which is included within prepaid expenses and other current assets in the accompanying balance sheets.
Stock-Based Compensation	Stock-Based Compensation ​ The Company accounts for stock-based compensation using ASC 718, Compensation – Stock Compensation (“ASC 718”), or ASC 505-50, Equity – Equity Based Payments to Non-Employees , as applicable. The Company accounts for stock-based awards to employees and non-employee directors using the fair value based method to determine compensation expense for all arrangements where shares of stock or equity instruments are issued for compensation. In addition, the Company accounts for stock-based compensation to other non-employees in accordance with the accounting guidance for equity instruments that are issued to entities or persons other than employees. ​ The Company recognizes all share-based payments to employees and directors as expense in the statements of operations based on their fair values. The Company records compensation expense on a straight-line basis over an award’s requisite service period, or vesting period, based on the award’s fair value at the date of grant. Vesting for time-based options and restricted stock units is generally four years for employees and one year for directors. The Company uses a Black-Scholes option-pricing model to determine the fair value of each option grant as of the date of grant for expense incurred. The Black-Scholes option pricing model requires inputs for risk-free interest rate, dividend yield, expected stock price volatility and expected term of the options. Forfeitures are accounted for as they occur. See Note 12, “Stock-based Compensation” for additional details.
Merger-related Costs, net	Merger-related Costs, net On January 21, 2018, the Company, BioCryst Pharmaceuticals, Inc., a Delaware corporation (“BioCryst”), Nautilus Holdco, Inc., a Delaware corporation and a direct, wholly owned subsidiary of BioCryst (“Holdco”), Island Merger Sub, Inc., a Delaware corporation and a direct, wholly owned subsidiary of Holdco, and Boat Merger Sub, Inc., a Delaware corporation and a direct, wholly owned subsidiary of Holdco, entered into an Agreement and Plan of Merger (the “Merger Agreement”). The board of directors of each of Idera and BioCryst unanimously approved the Merger Agreement and the transactions contemplated thereby and the required regulatory approvals were received. However, the proposed merger was subject to approval by the stockholders of Idera and BioCryst, and satisfaction of other customary closing conditions, as specified in the Merger Agreement. At a special meeting of BioCryst stockholders held on July 10, 2018, BioCryst’s stockholders voted against the adoption of the Merger Agreement. Following such vote and in accordance with the terms of the Merger Agreement, BioCryst terminated the Merger Agreement. In accordance with the Merger Agreement, BioCryst paid the Company a fixed expense reimbursement amount of $6 million in July 2018 in connection with the termination of the Merger Agreement. The fixed expense reimbursement amount is included in “Merger-related costs, net” in the accompanying statements of operations. ​ Merger-related costs, net includes amounts related to the transactions contemplated under the Merger Agreement, including charges incurred for transaction and integration-related professional fees, employee retention costs, and other incremental costs directly related to the potential merger; less the $6 million fixed expense reimbursement termination fee, which was received by the Company in July 2018.
Restructuring Costs	Restructuring Costs Restructuring charges are primarily comprised of severance costs related to workforce reductions, contract termination and wind-down costs and asset impairments. In accordance with ASC 420, Exit or Disposal Cost Obligations , the Company recognizes restructuring charges when the liability has been incurred, except for one-time employee termination benefits that are incurred over time. Generally, one-time employee termination benefits (i.e. severance costs) are accrued at the date management has committed to a plan of termination and employees have been notified of their termination dates and expected severance payments. Other costs will be recorded as incurred. Asset impairment charges have been, and will be, recognized when management has concluded that the assets have been impaired in accordance with ASC 360-10-35, Impairment or Disposal of Long-Lived Assets , or other applicable authoritative guidance. See Note 11 for additional details.
Income Taxes	Income Taxes ​ An asset and liability approach is used for financial accounting and reporting for income taxes. Deferred income taxes arise from temporary differences between income tax and financial reporting and principally relate to recognition of revenue and expenses in different periods for financial and tax accounting purposes and are measured using currently enacted tax rates and laws. In addition, a deferred tax asset can be generated by a net operating loss carryover. If it is more likely than not that some portion or all of a deferred tax asset will not be realized, a valuation allowance is recognized. ​ In the event the Company is charged interest or penalties related to income tax matters, the Company would record such interest as interest expense and would record such penalties as other expense in the Statements of Operations. No such charges have been incurred by the Company. For each of the years ended December 31, 2020, 2019 and 2018, the Company had no uncertain tax positions. See Note 14, “Income Taxes” for additional details.
Net Loss per Common Share applicable to Common Stockholders	Net Loss per Common Share applicable to Common Stockholders ​ Basic and diluted net loss per common share applicable to common stockholders is computed using the weighted average number of shares of common stock outstanding during the period. The diluted loss per share calculation gives effect to dilutive stock options, restricted stock units, warrants, convertible preferred stock and other potentially dilutive common stock equivalents outstanding during the period. Diluted loss per share is based on the if-converted method or the treasury stock method, as applicable, and includes the effect from the potential issuance of common stock, such as shares issuable pursuant to the conversion of convertible preferred stock and the exercise of stock options and warrants, assuming the exercise of all “in-the-money” common stock equivalents based on the average market price during the period. Common stock equivalents have been excluded where their inclusion would be anti-dilutive. Diluted net loss per common share applicable to common stockholders is the same as basic net loss per common share applicable to common stockholders for each of the three years in the period ended December 31, 2020 as the effects of the Company’s potential common stock equivalents are antidilutive (see Note 17).
New Accounting Pronouncements	New Accounting Pronouncements ​ From time to time, new accounting pronouncements are issued by the FASB and rules are issued by the SEC that the Company has or will adopt as of a specified date. Unless otherwise noted, management does not believe that any other recently issued accounting pronouncements issued by the FASB or guidance issued by the SEC had, or is expected to have, a material impact on the Company’s present or future financial statements. ​ Recently Adopted Accounting Pronouncements ​ In June 2016, the FASB issued Accounting Standard Update (“ASU”) No. 2016-13, Financial Instruments — Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). This standard requires that credit losses be reported using an expected losses model rather than the incurred losses model that is currently used, and establishes additional disclosures related to credit risks. For available-for-sale debt securities with unrealized losses, this standard now requires allowances to be recorded instead of reducing the amortized cost of the investment. The Company adopted ASU 2016-13 in the first quarter of 2020. The adoption of this ASU did not have a material effect on the Company’s financial statements. ​ In August 2018, the FASB issued ASU No. 2018-13, Disclosure Framework — Changes to the Disclosure Requirements for Fair Value Measurement (“ASU 2018-13”), which amends ASC 820, Fair Value Measurement . ASU 2018-13 modifies the disclosure requirements for fair value measurements by removing, modifying, or adding certain disclosures. The Company adopted ASU 2018-13 in the first quarter of 2020. The adoption of this ASU did not have a material effect on the Company’s financial statements. ​ Recently Issued (Not Yet Adopted) Accounting Pronouncements ​ In August 2020, the FASB issued ASU No. 2020-06, Debt—Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging—Contracts in Entity’s Own Equity (Subtopic 815-40): Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity (“ASU 2020-06”), which simplifies the guidance on an issuer’s accounting for convertible instruments and contracts in its own equity. The provisions of ASU 2020-06 are applicable for fiscal years beginning after December 15, 2021, with early adoption permitted no earlier than fiscal years beginning after December 15, 2020. The Company is currently evaluating the impact of ASU 2020-06 on its financial statements.
Accounting for Uncertainty in Income Taxes	The Company applies ASC 740-10, Accounting for Uncertainty in Income Taxes, an interpretation of ASC 740 . ASC 740-10 clarifies the accounting for uncertainty in income taxes recognized in financial statements and requires the impact of a tax position to be recognized in the financial statements if that position is more likely than not of being sustained by the taxing authority. The Company had no unrecognized tax benefits resulting from uncertain tax positions at December 31, 2020 and 2019.
COVID-19	COVID-19 ​ While the Company is not aware of a material impact from the novel coronavirus disease ("COVID-19") pandemic through December 31, 2020, the full extent to which COVID-19 will directly or indirectly impact the Company’s business, results of operations and financial condition, including expenses and manufacturing, clinical trials and research and development costs, depends on future developments that are highly uncertain at this time.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
Fair Value Measurements
Schedule of assets and liabilities measured and recorded in financial statements at fair value on a recurring basis	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 (In thousands) ​ Total ​ Level 1 ​ Level 2 ​ Level 3 Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash ​ $ 250 ​ $ 250 ​ $ — ​ $ — ​ Cash equivalents – money market funds ​ ​ 32,979 ​ ​ 32,979 ​ ​ — ​ ​ — ​ Short-term investments – commercial paper ​ 3,499 ​ — ​ 3,499 ​ — ​ Short-term investments – US treasury bills ​ 1,000 ​ — ​ 1,000 ​ — ​ Total assets ​ $ 37,728 ​ $ 33,229 ​ $ 4,499 ​ $ — ​ Liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Warrant liability ​ $ 6,983 ​ $ — ​ $ — ​ $ 6,983 ​ Future tranche right liability ​ ​ 118,803 ​ ​ — ​ ​ — ​ ​ 118,803 ​ Total liabilities ​ $ 125,786 ​ $ — ​ $ — ​ $ 125,786 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ (In thousands) ​ Total ​ Level 1 ​ Level 2 ​ Level 3 ​ Assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cash ​ $ 250 ​ $ 250 ​ $ — ​ $ — ​ Cash equivalents – money market funds ​ ​ 39,769 ​ ​ 39,769 ​ ​ — ​ ​ — ​ Short-term investments – commercial paper ​ 2,774 ​ — ​ 2,774 ​ — ​ Total assets ​ $ 42,793 ​ $ 40,019 ​ $ 2,774 ​ $ — ​ Liabilities ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Warrant liability ​ $ 3,241 ​ $ — ​ $ — ​ $ 3,241 ​ Future tranche right liability ​ ​ 46,436 ​ ​ — ​ ​ — ​ ​ 46,436 ​ Total liabilities ​ $ 49,677 ​ $ — ​ $ — ​ $ 49,677 ​
Schedule of reconciliation measured at fair value on a recurring basis using unobservable inputs	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Future ​ ​ Warrant ​ Tranche Right (In thousands) ​ Liability ​ Liability Balance, December 31, 2019 $ 3,241 ​ $ 46,436 Change in the fair value of liability 3,742 ​ 72,367 Balance, December 31, 2020 $ 6,983 ​ $ 118,803
Warrant liability
Fair Value Measurements
Schedule of assumptions used in determining fair value	​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 ​ 2019 Risk-free interest rate ​ 0.50% ​ ​ 1.79% Expected dividend yield ​ — ​ ​ — Expected term (years) ​ 5.98 ​ ​ 6.98 Expected volatility ​ 80% ​ ​ 80% Exercise price (per share) $ 1.52 ​ $ 1.52
Future tranche right liability
Fair Value Measurements
Schedule of assumptions used in determining fair value	​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ 2020 ​ 2019 Risk-free interest rate ​ 0.64% - 0.73% ​ ​ 1.84% - 1.88% Expected dividend yield ​ — ​ ​ — Expected term (years) of call options on preferred stock ​ 0.25 - 1.12 ​ ​ 1.16 - 2.16 Expected term (years) of warrants ​ 7.25 - 8.12 ​ ​ 8.16 - 9.16 Expected volatility ​ 80% ​ ​ 80% Exercise price (per share) for common stock equivalent for preferred stock and warrant $ 1.52 - 1.82 ​ $ 1.52 - 1.82

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2020
Investments
Schedule of available-for-sale investments at fair value	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2020 ​ ​ Gross Gross Estimated ​ ​ ​ ​ Unrealized ​ Unrealized ​ Fair ​ (In thousands) ​ Cost ​ (Losses) ​ Gains ​ Value ​ Short-term investments – commercial paper ​ $ 3,499 ​ $ — ​ $ — ​ $ 3,499 ​ Short-term investments – US treasury bills ​ ​ 1,000 ​ ​ — ​ ​ — ​ ​ 1,000 ​ Total short-term investments ​ $ 4,499 ​ $ — ​ $ — ​ $ 4,499 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, 2019 ​ ​ ​ ​ ​ Gross ​ Gross ​ Estimated ​ ​ ​ ​ ​ Unrealized ​ Unrealized ​ Fair (In thousands) Cost (Losses) Gains Value Short-term investments – commercial paper ​ $ 2,774 ​ $ — ​ $ — ​ $ 2,774 ​ Total short-term investments ​ $ 2,774 ​ $ — ​ $ — ​ $ 2,774 ​

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2020
Property and Equipment
Schedule of net property and equipment at cost	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ (In thousands) 2020 2019 Leasehold improvements ​ $ 107 ​ $ 107 ​ Equipment and other ​ 770 ​ 764 ​ Total property and equipment, at cost ​ $ 877 ​ $ 871 ​ Less: Accumulated depreciation and amortization ​ 833 ​ 774 ​ Property and equipment, net ​ $ 44 ​ $ 97 ​

Accrued Expenses (Tables)

Accrued Expenses (Tables)	12 Months Ended
	Dec. 31, 2020
Accrued Expenses
Schedule of accrued expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, (In thousands) ​ 2020 2019 Payroll and related costs ​ $ 2,133 ​ $ 2,179 ​ Clinical and nonclinical trial expenses ​ 3,229 ​ 4,199 ​ Professional and consulting fees ​ 584 ​ 859 ​ Restructuring expenses ​ — ​ 113 ​ Other ​ 126 ​ 111 ​ Total accrued expenses ​ $ 6,072 ​ $ 7,461 ​

Redeemable Convertible Prefer_2

Redeemable Convertible Preferred Stock (Tables)	12 Months Ended
	Dec. 31, 2020
Redeemable Convertible Preferred Stock
Schedule of Redeemable Convertible Preferred Stock	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Price Per ​ Aggregate Future Tranche Rights ​ Preferred Shares ​ Share ​ Purchase Price Tranche 2 (Series B2) (1) ​ 98,685 ​ $ 152 ​ $ 15,000,120 Tranche 3 (Series B3) (2) ​ 82,418 ​ $ 182 ​ ​ 15,000,076 Tranche 4 (Series B4) (2) ​ 82,418 ​ $ 182 ​ ​ 15,000,076 Total ​ 263,521 ​ ​ ​ ​ $ 45,000,272 (1) Accompanied by related warrants to purchase up to 9,868,500 shares of the Company’s common stock (or, if the holder elects to exercise the warrants for shares of Series B1 Preferred Stock, 98,685 shares of Series B1 Preferred Stock), at an exercise price of $1.52 per share (or, if the holder elects to exercise the warrants for Series B1 Preferred Stock, $152 per share of Series B1 Preferred Stock). (2) Accompanied by related warrants to purchase up to 6,593,440 shares of the Company’s common stock (or, if the holder elects to exercise the warrants for shares of Series B1 Preferred Stock, 65,934 shares of Series B1 Preferred Stock), at an exercise price of $1.82 per share (or, if the holder elects to exercise the warrants for Series B1 Preferred Stock, $182 per share of Series B1 Preferred Stock). ​

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2020
Stockholders' Equity
Schedule of warrants outstanding and exercisable for purchase of common stock	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Number of Shares ​ ​ ​ ​ ​ ​ ​ December 31, ​ December 31, ​ Weighted-Average ​ ​ ​ Description ​ 2020 ​ 2019 ​ Exercise Price ​ Expiration Date Liability-classified Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ December 2019 Series B1 warrants (1) ​ 2,368,400 ​ 2,368,400 ​ ​ $ 1.52 ​ Dec 2026 ​ ​ ​ 2,368,400 ​ 2,368,400 ​ ​ ​ ​ ​ ​ Equity-classified Warrants ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ May 2013 warrants 1,949,754 ​ 1,949,754 ​ ​ $ 0.08 ​ None ​ September 2013 warrants 514,756 ​ 514,756 ​ ​ $ 0.08 ​ None ​ February 2014 warrants 266,006 ​ 266,006 ​ ​ $ 0.08 ​ None ​ April 2020 Private Placement first closing warrants ​ 3,039,514 ​ — ​ ​ $ 2.28 ​ Apr 2023 ​ April 2020 Private Placement second closing warrants ​ 1,373,626 ​ — ​ ​ $ 2.71 ​ Dec 2023 ​ April 2020 Private Placement second closing warrants ​ 2,677,311 ​ — ​ ​ $ 0.01 ​ None ​ July 2020 Private Placement first closing warrants ​ 2,014,234 ​ — ​ ​ $ 0.01 ​ None ​ July 2020 Private Placement first closing warrants ​ 2,764,227 ​ — ​ ​ $ 2.58 ​ Jul 2023 ​ ​ ​ 14,599,428 ​ 2,730,516 ​ ​ ​ ​ ​ ​ Total outstanding 16,967,828 ​ 5,098,916 ​ ​ ​ ​ ​ ​ (1) The Series B1 warrants are exercisable for either common stock (exercise price of $1.52 ) or Series B1 Convertible Preferred Stock (exercise price of $152 ) at the discretion of the warrant holder.
Summary of warrant activity	​ ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Weighted-Average ​ ​ Warrants ​ Exercise Price Outstanding at December 31, 2019 5,098,916 ​ $ 0.75 Issued (1) 11,868,912 ​ 1.50 Exercised — ​ — Expired — ​ — Outstanding at December 31, 2020 16,967,828 ​ $ 1.28 (1) During th e year ended December 31, 2020, certain related parties were issued warrants as more fully described in Note 16.

Restructuring Costs (Tables)

Restructuring Costs (Tables)	12 Months Ended
	Dec. 31, 2020
Restructuring Costs
Schedule of restructuring costs	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ Employee Severance ​ Contract Termination Costs ​ Asset Impairments ​ Total Accrued restructuring balance as of December 31, 2017 $ — ​ $ — ​ $ — ​ $ — Charges incurred (1) ​ 2,635 ​ ​ 225 ​ ​ 674 ​ ​ 3,534 Cash payments ​ (1,380) ​ ​ (225) ​ ​ — ​ ​ (1,605) Non-cash settlements ​ (24) ​ ​ — ​ ​ (674) ​ ​ (698) Adjustments ​ ​ (84) ​ ​ — ​ ​ — ​ ​ (84) Accrued restructuring balance as of December 31, 2018 $ 1,147 ​ $ — ​ $ — ​ $ 1,147 Charges incurred ​ 181 ​ ​ — ​ ​ — ​ ​ 181 Cash payments ​ (1,215) ​ ​ — ​ ​ — ​ ​ (1,215) Accrued restructuring balance as of December 31, 2019 $ 113 ​ $ — $ — ​ $ 113 Charges incurred ​ — ​ ​ — ​ ​ — ​ ​ — Cash payments ​ (113) ​ ​ — ​ ​ — ​ ​ (113) Accrued restructuring balance as of December 31, 2020 $ — ​ $ — $ — ​ $ — (1) Excludes $0.4 million gain due to the write-off of the remaining deferred rent liability associated with the termination of the Cambridge, Massachusetts facility lease.

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2020
Stock-Based Compensation
Schedule of stock-based compensation expense attributable to share-based payments made to employees and directors and included in operating expenses	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ 2020 2019 2018 Stock-based compensation: ​ ​ ​ ​ ​ ​ ​ Research and development ​ ​ ​ ​ ​ ​ ​ ​ ​ Employee Stock Purchase Plan ​ $ 88 $ 36 $ 71 Equity Incentive Plan ​ ​ 673 ​ 1,312 ​ 1,780 ​ ​ $ 761 $ 1,348 $ 1,851 General and administrative ​ ​ ​ ​ ​ ​ ​ ​ ​ Employee Stock Purchase Plan ​ $ 9 $ 20 $ 48 Equity Incentive Plan ​ ​ 2,871 ​ 2,477 ​ 3,751 ​ ​ $ 2,880 $ 2,497 $ 3,799 Restructuring costs ​ ​ ​ ​ ​ ​ ​ ​ ​ Equity Incentive Plan ​ $ — ​ $ — ​ $ 24 ​ ​ $ — ​ $ — ​ $ 24 Total stock-based compensation expense ​ $ 3,641 $ 3,845 $ 5,674
Schedule of weighted average assumptions applied to options	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2019 ​ 2018 ​ Average risk-free interest rate ​ ​ 1.0% ​ ​ 2.1% ​ ​ 2.5% ​ Expected dividend yield ​ ​ — ​ ​ — ​ ​ — ​ Expected lives (years) ​ ​ 3.9 ​ ​ 3.7 ​ ​ 3.7 ​ Expected volatility ​ ​ 84% ​ ​ 84% ​ ​ 74% ​ Weighted average exercise price (per share) ​ $ 2.08 ​ $ 2.75 ​ $ 12.63 ​
Schedule of information related to outstanding and exercisable options	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ($ in thousands, except per share data) ​ Stock ​ Weighted-Average ​ Weighted-Average ​ Aggregate Intrinsic Value Outstanding at December 31, 2019 4,220,417 ​ $ 13.08 6.6 ​ $ — ​ Granted 1,215,382 ​ 2.08 ​ ​ ​ ​ ​ ​ Exercised (5,265) ​ 2.84 ​ ​ ​ ​ ​ ​ Forfeited (206,323) ​ 6.12 ​ ​ ​ ​ ​ ​ Expired (609,888) ​ 18.61 ​ ​ ​ ​ ​ ​ Outstanding at December 31, 2020 (1) 4,614,323 ​ $ 9.78 6.8 ​ $ 2,949 ​ Exercisable at December 31, 2020 2,490,179 ​ $ 15.12 5.2 ​ $ 455 ​ (1) Includes both vested stock options as well as unvested stock options for which the requisite service period has not been rendered but that are expected to vest based on achievement of a service condition.
Schedule of summary of restricted stock activity	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Time-based Awards ​ Market/Performance-based Awards ($ in thousands, except per share data) ​ Number of Shares ​ Weighted-Average ​ Number of Shares ​ Weighted-Average Nonvested shares at December 31, 2019 193,625 ​ $ 3.14 ​ — ​ $ — Granted 365,845 ​ 2.65 ​ 556,888 ​ 1.54 Cancelled (28,895) ​ 2.75 ​ (7,570) ​ 1.54 Vested (176,572) ​ 3.95 ​ — ​ — Nonvested shares at December 31, 2020 354,003 ​ $ 2.27 ​ 549,318 ​ $ 1.54

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2020
Commitments and Contingencies
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	​ ​ ​ ​ ​ ​ ​ ​ December 31, ​ Operating Leases (in thousands) 2021 ​ 244 ​ 2022 ​ ​ 249 ​ 2023 ​ ​ 250 ​ 2024 ​ ​ 240 ​ 2025 ​ 101 ​ ​ ​ $ 1,084 ​

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Taxes
Schedule of components of deferred tax assets	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ 2020 2019 Operating loss carryforwards ​ $ 90,895 ​ $ 81,403 ​ Tax credit carryforwards ​ 26,550 ​ 23,072 ​ Stock-based compensation ​ ​ 6,820 ​ ​ 7,818 ​ Lease liabilities ​ ​ 276 ​ ​ 308 ​ Other ​ 162 ​ 176 ​ Total deferred tax assets ​ 124,703 ​ 112,777 ​ Right-of-use asset ​ ​ (270) ​ ​ (306) ​ Valuation allowance ​ (124,433) ​ (112,471) ​ Net deferred tax assets ​ $ — ​ $ — ​
Schedule of difference between U.S. federal corporate tax rate and Company effective tax rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2020 ​ 2019 ​ 2018 Expected federal income tax rate (21.0) % ​ (21.0) % ​ (21.0) % Expiring credits and NOLs — ​ ​ — ​ ​ 1.0 ​ Change in valuation allowance 10.6 ​ ​ 26.2 ​ ​ 37.9 ​ Federal and state credits (3.1) ​ ​ (8.1) ​ ​ (7.4) ​ State income taxes, net of federal benefit (1.9) ​ ​ (4.7) ​ ​ (9.7) ​ Warrant and future tranche right revaluation loss ​ 14.2 ​ ​ 4.3 ​ ​ — ​ Stock-based compensation 0.2 ​ ​ 0.5 ​ ​ 0.5 ​ Other 1.0 ​ ​ 2.8 ​ ​ (1.3) ​ Effective tax rate 0.0 % ​ 0.0 % ​ 0.0 %

Net Loss per Common Share App_2

Net Loss per Common Share Applicable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2020
Net Loss per Common Share Applicable to Common Stockholders
Schedule of potentially dilutive securities excluded from diluted net income (loss) per common share	​ ​ ​ ​ ​ ​ ​ ​ ​ (in thousands) ​ 2020 ​ ​ 2019 ​ 2018 Stock options ​ 4,614 ​ ​ 4,220 ​ 3,305 Restricted stock units ​ 903 ​ ​ 194 ​ — Common stock warrants ​ 16,968 ​ ​ 5,099 ​ 2,769 Convertible preferred stock ​ 2,369 ​ ​ 2,369 ​ 1 Future tranche rights ​ 50,467 ​ ​ 49,407 ​ — Total ​ 75,321 ​ ​ 61,289 ​ 6,075

Business and Organization (Deta

Business and Organization (Details) - USD ($) $ in Thousands	2 Months Ended
	Feb. 28, 2021	Dec. 31, 2020	Dec. 31, 2019
Business and Organization
Accumulated deficit		$ 833,552	$ 720,890
Cash, cash equivalents and investments		$ 37,700
Net proceeds from offering of common stock	$ 16,300

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2018USD ($)	Dec. 31, 2020USD ($)Institutionsegment	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Oct. 31, 2020USD ($)
Accounting Policies
Number of operating segments | segment		1
Number of financial institutions | Institution		2
Short-term financing arrangement					$ 600
Other current liability		$ 435
Operating lease right-of-use assets		930	$ 1,054
Operating lease liability		$ 191	163
Practical Expedient, Financing Component		true
Prepaid expenses research and development		$ 2,500	2,800
Charges incurred		0	0	$ 0
Uncertain tax positions		$ 0	$ 0	$ 0
Minimum
Accounting Policies
Equipment depreciation period		3 years
Maximum
Accounting Policies
Equipment depreciation period		5 years
Employees
Accounting Policies
Stock options, vesting period		4 years
Board of Director
Accounting Policies
Stock options, vesting period		1 year
BioCryst
Accounting Policies
Fixed expense reimbursement	$ 6,000

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - New Accounting Pronouncements (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements - Recently Issued
Operating lease right-of-use assets	$ 930	$ 1,054

Fair Value Measurements - Trans

Fair Value Measurements - Transfers Between Levels (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Fair Value Measurements
Fair value of assets transfers from level 1 to level 2	$ 0
Fair value of assets transfers from level 2 to level 1	0
Fair value of liabilities transfers from level 1 to level 2	0
Fair value of liabilities transfers from level 2 to level 1	0
Fair value of assets transfers into level 3	0
Fair value of assets transfers out of level 3	0
Fair value of liabilities transfers into level 3	0
Fair value of liabilities transfers out of level 3	$ 0

Fair Value Measurements - Asset

Fair Value Measurements - Assets and Liabilities at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments	$ 4,499	$ 2,774
Fair value on a recurring basis
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Assets	37,728	42,793
Total Liabilities	125,786	49,677
Fair value on a recurring basis | Warrant liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities	6,983	3,241
Fair value on a recurring basis | Future tranche right liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities	118,803	46,436
Fair value on a recurring basis | Cash
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash and Money market funds	250	250
Fair value on a recurring basis | Money market funds
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash and Money market funds	32,979	39,769
Fair value on a recurring basis | Short-term investments - commercial paper
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments	3,499	2,774
Fair value on a recurring basis | Short-term investments - U.S. treasury bills
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments	1,000
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) | Fair value on a recurring basis
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Assets	33,229	40,019
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) | Fair value on a recurring basis | Cash
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash and Money market funds	250	250
Quoted Prices in Active Markets for Identical Assets or Liabilities (Level 1) | Fair value on a recurring basis | Money market funds
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash and Money market funds	32,979	39,769
Significant Other Observable Inputs (Level 2) | Fair value on a recurring basis
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Assets	4,499	2,774
Significant Other Observable Inputs (Level 2) | Fair value on a recurring basis | Short-term investments - commercial paper
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments	3,499	2,774
Significant Other Observable Inputs (Level 2) | Fair value on a recurring basis | Short-term investments - U.S. treasury bills
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Cash equivalents and Short-term investments	1,000
Significant Other Unobservable Inputs (Level 3) | Fair value on a recurring basis
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities	125,786	49,677
Significant Other Unobservable Inputs (Level 3) | Fair value on a recurring basis | Warrant liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities	6,983	3,241
Significant Other Unobservable Inputs (Level 3) | Fair value on a recurring basis | Future tranche right liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Total Liabilities	$ 118,803	$ 46,436

Fair Value Measurements - Ass_2

Fair Value Measurements - Assets and Liabilities at Fair Value Changes in Level 3 Liabilities (Details) - Fair value on a recurring basis $ in Thousands	12 Months Ended
	Dec. 31, 2020USD ($)
Warrant liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Beginning balance	$ 3,241
Change in the fair value of liability	3,742
Ending balance	6,983
Future tranche right liability
Fair Value of Assets and Liabilities Measured at Fair Value on a Recurring Basis
Beginning balance	46,436
Change in the fair value of liability	72,367
Ending balance	$ 118,803

Fair Value Measurements - Weigh

Fair Value Measurements - Weighted-average assumptions (Details)	Dec. 31, 2020$ / shares	Dec. 31, 2019$ / shares
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.0050	0.0179
Expected term
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.0598	0.0698
Expected volatility
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.80	0.80
Exercise price
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	1.52	1.52

Fair Value Measurements - Futur

Fair Value Measurements - Future Tranche Rights (Details)	Dec. 31, 2020$ / sharesUSD ($)	Dec. 31, 2019$ / shares
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.0050	0.0179
Risk-free interest rate | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.64
Risk-free interest rate | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.73
Risk-free interest rate | Preferred stock | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input		1.84
Risk-free interest rate | Preferred stock | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input		1.88
Expected term
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.0598	0.0698
Expected term | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.25
Expected term | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	1.12
Expected term | Warrants | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	7.25	8.16
Expected term | Warrants | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	8.12	9.16
Expected term | Preferred stock | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input		1.16
Expected term | Preferred stock | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input		2.16
Expected volatility
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	0.80	0.80
Expected volatility | Future tranche right liability
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	80	80
Exercise price
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input | $ / shares	1.52	1.52
Exercise price | Future tranche right liability | Minimum
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	1.52	1.52
Exercise price | Future tranche right liability | Maximum
Fair Value Measurement Inputs and Valuation Techniques
Debt instrument measurement input	1.82	1.82

Investments - Summary of Availa

Investments - Summary of Available-for-Sale Investments at Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Short-term investments
Schedule of Available-for-sale Securities
Cost	$ 4,499	$ 2,774
Estimated Fair Value	4,499	2,774
Short-term investments - commercial paper
Schedule of Available-for-sale Securities
Cost	3,499	2,774
Estimated Fair Value	3,499	$ 2,774
Short-term investments - U.S. treasury bills
Schedule of Available-for-sale Securities
Cost	1
Estimated Fair Value	$ 1

Investments - Additional Inform

Investments - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Investments
Realized gains or losses	$ 0	$ 0
Allowance for credit losses on available-for-sale debt securities	0	0
Losses or other-than-temporary declines	$ 0	$ 0

Property and Equipment - Net Pr

Property and Equipment - Net Property and Equipment at Cost (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment
Total property and equipment, at cost	$ 877	$ 871
Less: Accumulated depreciation and amortization	833	774
Property and equipment, net	44	97
Leasehold improvements
Property, Plant and Equipment
Total property and equipment, at cost	107	107
Laboratory equipment and other
Property, Plant and Equipment
Total property and equipment, at cost	$ 770	$ 764

Property and Equipment - Deprec

Property and Equipment - Depreciation and Amortization Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Property and Equipment
Depreciation and amortization expense on property and equipment	$ 0.1	$ 0.1	$ 0.4
Fixed asset impairments	$ 0	$ 0	$ 0.5

Accrued Expenses (Details)

Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accrued Expenses
Payroll and related costs	$ 2,133	$ 2,179
Clinical and nonclinical trial expenses	3,229	4,199
Professional and consulting fees	584	859
Restructuring expenses		113
Other	126	111
Total accrued expenses	$ 6,072	$ 7,461

Redeemable Convertible Prefer_3

Redeemable Convertible Preferred Stock (Details) - USD ($)	Dec. 23, 2019	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2018
Temporary Equity
Warrant exercise price (per share)		$ 0.75	$ 1.28
Aggregate gross proceeds	$ 3,900,000	$ 10,072,000
Gross proceeds	$ 6,200,000
Common Stock, Shares Authorized		140,000,000	140,000,000
Common stock trading Price	$ 7.60
Common stock trading Price, Number of trading days	20 days
Common stock trading Price, Number of trading days Subsequent to closing	30 days
Aggregate gross proceeds	$ 87,600,000
Baker Bros. Advisors LP
Temporary Equity
Warrant exercise price (per share)				$ 3.76
Deemed Dividend	28,000,000
Preferred Stock Warrant
Temporary Equity
Preferred Shares			263,521
Aggregate Purchase Price			$ 45,000,272
Series B1 Warrants
Temporary Equity
Gross proceeds received	10,100,000
Estimated fair values	2,600,000
Future Tranche Rights
Temporary Equity
Estimated fair values	$ 35,500,000
Series B1 Redeemable Convertible Preferred Stock
Temporary Equity
Sale of redeemable convertible preferred stock	23,684	24,000
Series B1 Redeemable Convertible Preferred Stock | Common Stock Warrants
Temporary Equity
Warrant to purchase common stock	2,368,400
Warrant exercise price (per share)	$ 1.52
Series B1 Redeemable Convertible Preferred Stock | Preferred Stock Warrant
Temporary Equity
Warrant to purchase common stock	23,684
Warrant exercise price (per share)	$ 152
Series B2 Redeemable Convertible Preferred Stock | Common Stock Warrants
Temporary Equity
Warrant to purchase common stock	9,868,500
Warrant exercise price (per share)	$ 1.52
Series B2 Redeemable Convertible Preferred Stock | Preferred Stock Warrant
Temporary Equity
Warrant to purchase common stock	98,685
Warrant exercise price (per share)	$ 152
Preferred Shares			98,685
Share Price			$ 152
Aggregate Purchase Price			$ 15,000,120
Series B3 Redeemable Convertible Preferred Stock | Common Stock Warrants
Temporary Equity
Warrant to purchase common stock	6,593,440
Warrant exercise price (per share)	$ 1.82
Series B3 Redeemable Convertible Preferred Stock | Preferred Stock Warrant
Temporary Equity
Warrant to purchase common stock	65,934
Warrant exercise price (per share)	$ 182
Preferred Shares			82,418
Share Price			$ 182
Aggregate Purchase Price			$ 15,000,076
Series B4 Redeemable Convertible Preferred Stock
Temporary Equity
Expiration period	21 months
Series B4 Redeemable Convertible Preferred Stock | Preferred Stock Warrant
Temporary Equity
Preferred Shares			82,418
Share Price			$ 182
Aggregate Purchase Price			$ 15,000,076

Stockholders' Equity - Preferre

Stockholders' Equity - Preferred Stock (Details)	12 Months Ended
	Dec. 31, 2020item$ / sharesshares	Dec. 31, 2019$ / sharesshares
Class of Stock
Preferred stock, calendar days | item	180
Average Trading volume days | item	50
Preferred stock, shares issued	500,000
Series A Convertible Preferred Stock
Class of Stock
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, par value | $ / shares	$ 0.01	$ 0.01
Preferred stock, shares designated	1,500,000	1,500,000
Annual percentage of dividend of preferred stock	1.00%
Preferred stock, shares outstanding	655	655
Series A preferred stock liquidation preference per share | $ / shares	$ 1
Series A Preferred stock conversion price per share | $ / shares	$ 272
Preferred stock, shares issued	1,000	1,000
Series B1 Redeemable Convertible Preferred Stock
Class of Stock
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, par value | $ / shares	$ 0.01	$ 0.01
Preferred stock, shares designated	277,921	278,000
Preferred stock, shares outstanding	24,000	24,000
Preferred stock redemption price per share | $ / shares	$ 152
Preferred stock conversion price | $ / shares	$ 1.52
Preferred stock, shares issued	24,000	24,000
Series B2 Redeemable Convertible Preferred Stock
Class of Stock
Preferred stock, shares designated	98,685
Preferred stock, shares outstanding	0	0
Preferred stock redemption price per share | $ / shares	$ 152
Preferred stock conversion price | $ / shares	$ 1.52
Series B3 Redeemable Convertible Preferred Stock
Class of Stock
Preferred stock, shares designated	82,814
Preferred stock, shares outstanding	0	0
Preferred stock redemption price per share | $ / shares	$ 182
Preferred stock conversion price | $ / shares	$ 1.82
Series B4 Redeemable Convertible Preferred Stock
Class of Stock
Preferred stock, shares designated	82,814
Preferred stock, shares outstanding	0	0
Preferred stock redemption price per share | $ / shares	$ 182
Preferred stock conversion price | $ / shares	$ 1.82

Stockholders' Equity - Common S

Stockholders' Equity - Common Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Dec. 11, 2020	Jul. 13, 2020	Apr. 07, 2020	Dec. 23, 2019	Mar. 04, 2019	May 05, 1998	Nov. 30, 2018	Feb. 28, 2021	Dec. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Stock
Par value (per share)									$ 0.001	$ 0.001	$ 0.001
Shares authorized (in shares)									140,000,000	140,000,000	140,000,000
Proceeds from issuance				$ 3,900							$ 10,072
Warrant exercise price (per share)									$ 1.28	$ 1.28	$ 0.75
Net proceeds from offering of common stock								$ 16,300
Common stock, shares reserved for future issuance									35,750,149	35,750,149
Board of Director
Class of Stock
Ownership percentage									12.00%	12.00%
"At-The-Market" Equity Program
Class of Stock
Maximum value of shares that are permitted to be sold, subject to certain limitations										$ 35,400
Stock issued (in shares)										3,608,713	532,700
Net proceeds from offering of common stock												$ 0
Percentage of fixed commission expense of gross proceeds of shares sold in ATM agreement							3.00%
Net proceeds from offering of common stock										$ 12,300	$ 1,600
Lincoln Park Capital Fund, LLC ("Investor")
Class of Stock
Value of shares investor has committed to purchase					$ 35,000
Maximum value of shares that are permitted to be sold, subject to certain limitations										$ 29,500
Stock issued (in shares)					269,749					750,000	1,535,848
Stock issued (per share)					$ 2.84
Net proceeds from offering of common stock										$ 1,700	$ 3,700
Common Stock
Class of Stock
Stock issued (in shares)						149,960
Sale price of common shares subject to the liquidation put						$ 128
Minimum closing sales price of common stock to issue termination notice to put holders										$ 256
Price exceeds on number of days										20 days
Liquidation put shares no longer held by original holders										49,993
Shares held by put holders										4,472
Put Rights outstanding										0
Remaining shares of common stock subject to the liquidation put										95,494
Common Stock | "At-The-Market" Equity Program
Class of Stock
Net proceeds from offering of common stock							$ 50,000
April 2020 Private Placement
Class of Stock
Stock issued (in shares)			3,039,514
Shares of common stock that may be purchased upon exercise of warrants	0.5		3,039,514
Proceeds from issuance	$ 5,000		$ 5,000
Warrant exercise price (per share)			$ 2.28
Combined purchase price (per share)			1.645
Stock price underlying warrants (per share)			$ 0.125
April 2020 Private Placement | Common Stock Warrants
Class of Stock
Stock issued (in shares)	69,941
Warrant exercise price (per share)	$ 1.82
April 2020 Private Placement | Pre-funded Warrants
Class of Stock
Stock issued (in shares)	2,677,311
Warrant exercise price (per share)	$ 0.01								$ 0.5	$ 0.5
April 2020 Private Placement | Warrants
Class of Stock
Stock issued (in shares)	1,373,626
Warrant exercise price (per share)	$ 2.71								$ 1.81	$ 1.81
April 2020 Private Placement and April 2020 Private Placement Second Closing in Aggregate
Class of Stock
Net proceeds from offering of common stock									$ 9,800
July 2020 Private Placement
Class of Stock
Stock issued (in shares)		749,993
Proceeds from issuance		$ 5,100
Combined purchase price (per share)		$ 1.845
Stock price underlying warrants (per share)		$ 0.125
July 2020 Private Placement | Pre-funded Warrants
Class of Stock
Shares of common stock that may be purchased upon exercise of warrants		2,014,234
Warrant exercise price (per share)		$ 0.01
July 2020 Private Placement | Warrants
Class of Stock
Shares of common stock that may be purchased upon exercise of warrants		2,764,227
Warrant exercise price (per share)		$ 2.58
July 2020 Private Placement Second Closing
Class of Stock
Stock issued (in shares)		784,615
Shares of common stock that may be purchased upon exercise of warrants		274,615
Warrant exercise price (per share)		$ 9.75
Gross proceeds from sale of common stock and warrants excluding the proceeds from exercise of the warrants, if any		$ 5,100
Stock price (in dollars per share)		$ 0.01
Combined purchase price (per share)		$ 6.50
July 2020 Private Placement Second Closing | Common Stock Warrants
Class of Stock
Number of common warrants		0.35
Stock price (in dollars per share)		$ 0.04375
July 2020 Private Placement Second Closing | Pre-funded Warrants
Class of Stock
Warrant exercise price (per share)		$ 6.45625
July 2020 Private Placement and July 2020 Private Placement Second Closing in Aggregate
Class of Stock
Net proceeds from offering of common stock										$ 5,000

Stockholders' Equity - Reverse

Stockholders' Equity - Reverse Stock Split (Details) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Stockholders' Equity
Common stock, shares authorized	140,000,000	140,000,000
Common stock, par value	$ 0.001	$ 0.001

Stockholders' Equity - Common_2

Stockholders' Equity - Common Stock Warrants (Details) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
Class of Warrant or Right
Number of Warrants	16,967,828	5,098,916
Warrant exercise price per share	$ 1.28	$ 0.75
Warrants
Class of Warrant or Right
Warrant exercise price per share		1.52
Preferred stock
Class of Warrant or Right
Warrant exercise price per share		$ 152
Liability Classified Warrants
Class of Warrant or Right
Number of Warrants	2,368,400	2,368,400
December 2019 Series B1 warrants
Class of Warrant or Right
Number of Warrants	2,368,400	2,368,400
Warrant exercise price per share	$ 1.52	$ 1.52
Equity Classified Warrants
Class of Warrant or Right
Number of Warrants	14,599,428	2,730,516
May 2013 Warrants
Class of Warrant or Right
Number of Warrants	1,949,754	1,949,754
Warrant exercise price per share	$ 0.08	$ 0.08
September 2013 Warrants
Class of Warrant or Right
Number of Warrants	514,756	514,756
Warrant exercise price per share	$ 0.08	$ 0.08
February 2014 Warrants
Class of Warrant or Right
Number of Warrants	266,006	266,006
Warrant exercise price per share	$ 0.08	$ 0.08
April 2020 Private Placement first closing warrants
Class of Warrant or Right
Number of Warrants	3,039,514
Warrant exercise price per share	$ 2.28
April 2020 Private Placement second closing warrants
Class of Warrant or Right
Number of Warrants	1,373,626
Warrant exercise price per share	$ 2.71
April 2020 Private Placement second closing warrants
Class of Warrant or Right
Number of Warrants	2,677,311
Warrant exercise price per share	$ 0.01
July 2020 Private Placement first closing warrants
Class of Warrant or Right
Number of Warrants	2,014,234
Warrant exercise price per share	$ 0.01
July 2020 Private Placement first closing warrants
Class of Warrant or Right
Number of Warrants	2,764,227
Warrant exercise price per share	$ 2.58

Stockholders' Equity - Common_3

Stockholders' Equity - Common Stock Warrant Activity (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Class of Warrant or Right
Outstanding warrants, beginning of period	5,098,916
Outstanding warrants, end of period	16,967,828
Warrant exercise price (per share)	$ 1.28	$ 0.75
Expiration Date - November 2017
Class of Warrant or Right
Issued	11,868,912
Warrant exercise price (per share)	$ 1.50

Alliance Revenue (Details)

Alliance Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Alliance Revenue
Alliance revenue	$ 1,448	$ 662
Deferred revenue recognized during the period		$ 600
Out-license arrangement
Alliance Revenue
Alliance revenue	1,400
Gsk Collaboration
Alliance Revenue
Alliance revenue	500
Other
Alliance Revenue
Alliance revenue	$ 200

Collaboration and License Agr_2

Collaboration and License Agreements (Details) $ in Thousands	1 Months Ended		12 Months Ended
	Apr. 30, 2019USD ($)	Nov. 30, 2015USD ($)person	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Alliance revenue				$ 1,448	$ 662
Deferred revenue recognized during the period					600
Operating expenses			$ 36,687	47,515	61,618
Option and License Agreement with Licensee
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Transaction price				$ 1,400
Performance obligation			$ 0
Percentage of shares acquired	10.00%		10.00%	10.00%
Option and License Agreement with Licensee | Other Assets
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Value of securities without a readily determinable fair value			$ 100
Gsk Collaboration
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Alliance revenue				$ 500
Number of development candidates | person		1
GSK Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Alliance revenue			$ 0	$ 0	$ 500
Number of additional research periods					36 months
Number of development candidates | person		1
Number of optional additional targets | person		2
Research period		2 years
GSK Agreement | Up-front Payment Arrangement
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Upfront payment received under collaboration agreement		$ 2,500			$ 2,500
GSK Agreement | License, Research, Clinical Development and Commercialization
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments		100,000
GSK Agreement | Research and Development Plans and Designation of Development Candidates
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments		9,000
GSK Agreement | Clinical and Commercial Milestones
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Milestone payments		$ 89,000
IMO-9200 License | Option and License Agreement with Licensee
Collaborative Arrangements and Non-collaborative Arrangement Transactions
Upfront payment received under collaboration agreement	$ 1,400

Restructuring Costs (Details)

Restructuring Costs (Details) $ in Thousands	1 Months Ended	12 Months Ended			18 Months Ended
	Jul. 31, 2018employee	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2019USD ($)
Restructuring costs
Restructuring costs			$ 181	$ 3,112
Fixed asset impairments		$ 0	0	500
Cambridge, Massachusetts facility operations
Restructuring costs
Number of positions eliminated | employee	18
Percentage of positions eliminated	40.00%
Number of positions eliminated since inception | employee	15
Restructuring costs			$ 181	$ 3,534	$ 3,300
Non-cash asset impairments					700
Non-cash gain due to write-off of remaining deferred rent liability					400
Fixed asset impairments					500
Expenses associated with lease termination or prepaid expenses					200
Termination costs in connection with the reduction in workforce, including severance, benefits and related costs					$ 2,800

Restructuring Costs - Accrual R

Restructuring Costs - Accrual Rollforward (Details) - USD ($) $ in Thousands	12 Months Ended			18 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2019
Restructuring costs
Charges incurred		$ 181	$ 3,112
Cambridge, Massachusetts facility operations
Restructuring costs
Accrued restructuring balance, beginning of period	$ 113	1,147
Charges incurred		181	3,534	$ 3,300
Cash payments	(113)	(1,215)	(1,605)
Non-cash settlements			(698)
Adjustments			(84)
Accrued restructuring balance, end of period		113	1,147	113
Cambridge, Massachusetts facility operations | Employee Severance and Benefits
Restructuring costs
Accrued restructuring balance, beginning of period	113	1,147
Charges incurred		181	2,635
Cash payments	$ (113)	(1,215)	(1,380)
Non-cash settlements			(24)
Adjustments			(84)
Accrued restructuring balance, end of period		$ 113	1,147	$ 113
Cambridge, Massachusetts facility operations | Contract Termination Costs
Restructuring costs
Charges incurred			225
Cash payments			(225)
Cambridge, Massachusetts facility operations | Asset Impairments
Restructuring costs
Charges incurred			674
Non-cash settlements			$ (674)

Stock-Based Compensation - Equi

Stock-Based Compensation - Equity Incentive Plans (Details) - shares	Jul. 26, 2013	Dec. 31, 2020	Dec. 31, 2019
Class of Stock
Common stock, shares reserved for future issuance		35,750,149
Common stock options outstanding		4,614,323	4,220,417
Options outstanding under earlier plans		220,408
Grant of inducement stock option		359,375
2013 Stock Incentive Plan | 2013 Stock Incentive Plan
Class of Stock
Common shares available for grant	5,653,057	838,800
Maximum number of additional common shares	868,372
Common stock options outstanding		4,034,540
Restricted stock units outstanding		903,321

Stock-Based Compensation - Empl

Stock-Based Compensation - Employee Stock Purchase Plans (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jun. 07, 2017
Class of Stock
Proceeds from employee stock purchases	$ 113,000	$ 121,000	$ 243,000
2017 Employee Stock Purchase Plan
Class of Stock
Maximum percentage of total combined voting power or value of the stock of the Company after the grant	5.00%
Common shares available for grant		245,342
Employee Stock Purchase Plan
Class of Stock
Minimum percentage in payroll of deduction base salary to acquire shares of common stock	1.00%
Maximum percentage in payroll of deduction base salary to acquire shares of common stock	10.00%
Percentage of fair market value of common stock for the ESPP option price	85.00%
Annual maximum a participant may purchase under the employee stock purchase plan	$ 25,000
Common stock share issued	75,999	60,953	24,824
Defined Contribution Plan, Cost	$ 100,000	$ 100,000	$ 200,000
Maximum | 2017 Employee Stock Purchase Plan
Class of Stock
Common stock shares authorized for issuance under stock purchase plan				412,500
Maximum | Employee Stock Purchase Plan
Class of Stock
Subsequent offering period as established by the compensation committee	12 months

Stock-Based Compensation - Acco

Stock-Based Compensation - Accounting for Stock-based Compensation (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Percentage of share-based compensation expense	15.00%
Weighted average grant date fair value of options granted during the period (per share)	$ 1.25	$ 1.64	$ 7
Stock-based compensation	$ 3,641	$ 3,845	$ 5,674
Research and development
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	761	1,348	1,851
Research and development | Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	88	36	71
Research and development | Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	673	1,312	1,780
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	2,880	2,497	3,799
General and administrative | Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	9	20	48
General and administrative | Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation	$ 2,871	$ 2,477	3,751
Restructuring costs
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation			24
Restructuring costs | Equity Incentive Plans
Share-based Compensation Arrangement by Share-based Payment Award
Stock-based compensation			$ 24

Stock-Based Compensation - Assu

Stock-Based Compensation - Assumptions Used in Determining Fair Value of Stock Options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-Based Compensation
Options to purchase common stock granted to employees and directors	1,215,382	1,279,016	1,136,874
Average risk free interest rate	1.00%	2.10%	2.50%
Dividend rate	0.00%
Expected lives (years)	3 years 10 months 24 days	3 years 8 months 12 days	3 years 8 months 12 days
Expected volatility	84.00%	84.00%	74.00%
Weighted average exercise price of options granted during the period (per share)	$ 2.08	$ 2.75	$ 12.63

Stock-Based Compensation - Stoc

Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-Based Compensation
Options, Outstanding, Beginning Balance	4,220,417
Granted	1,215,382
Exercised	(5,265)
Forfeited	(206,323)
Expired	(609,888)
Options, Outstanding, Ending Balance	4,614,323	4,220,417
Exercisable, Ending Balance	2,490,179
Weighted Average Exercise Price, Beginning Balance	$ 13.08
Granted, Weighted Average Exercise Price	2.08	$ 2.75	$ 12.63
Exercised, Weighted Average Exercise Price	2.84
Forfeited, Weighted Average Exercise Price	6.12
Expired, Weighted Average Exercise Price	18.61
Weighted Average Exercise Price, Ending Balance	9.78	$ 13.08
Exercisable, Weighted Average Exercise Price	$ 15.12
Outstanding, Ending balance, Weighted Average Remaining Contractual Term	6 years 9 months 18 days	6 years 7 months 6 days
Exercisable Ending Balance, Weighted Average Remaining Contractual Term	5 years 2 months 12 days
Outstanding, Intrinsic Value, Ending Balance	$ 2,949
Exercisable, Ending Balance, Intrinsic Value	455
Fair value of options, vested	2,900
Unrecognized compensation cost related to nonvested stock-based compensation	$ 3,500
Weighted average remaining period over which unrecognized compensation expense will be recognized	2 years 2 months 12 days

Stock-Based Compensation - Rest

Stock-Based Compensation - Restricted Stock Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Jul. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Restricted Stock Activity, Weighted-Average Grant Date Fair Value
Unrecognized compensation expense		$ 3,500
Weighted average remaining period over which unrecognized compensation expense will be recognized		2 years 2 months 12 days
Share-based compensation		$ 3,641	$ 3,845	$ 5,674
Restricted stock units
Restricted Stock Activity, Number of Shares
Nonvested shares, Beginning Balance		193,625
Granted		365,845
Cancelled		(28,895)
Vested		(176,572)
Nonvested shares, Ending Balance		354,003	193,625
Restricted Stock Activity, Weighted-Average Grant Date Fair Value
Nonvested shares, Weighted Average Grant Date Fair Value, Beginning Balance		$ 3.14
Granted, Weighted-Average Grant Date Fair Value		2.65
Cancelled, Weighted-Average Grant Date Fair Value		2.75
Vested, Weighted-Average Grant Date Fair Value		3.95
Nonvested shares, Weighted Average Grant Date Fair Value, Ending Balance		$ 2.27	$ 3.14
Unrecognized compensation expense		$ 700
Weighted average remaining period over which unrecognized compensation expense will be recognized		1 year 10 months 24 days
Restricted stock units | 2013 Stock Incentive Plan
Restricted Stock Activity, Number of Shares
Granted		128,170
Market/Performance-based Awards
Restricted Stock Activity, Number of Shares
Granted		556,888
Cancelled		(7,570)
Nonvested shares, Ending Balance		549,318
Restricted Stock Activity, Weighted-Average Grant Date Fair Value
Granted, Weighted-Average Grant Date Fair Value		$ 1.54
Cancelled, Weighted-Average Grant Date Fair Value		1.54
Nonvested shares, Weighted Average Grant Date Fair Value, Ending Balance		$ 1.54
Weighted average remaining period over which unrecognized compensation expense will be recognized		1 year 6 months
Requisite service period (in years)	2 years 4 months 9 days
Share-based compensation		$ 200
Unrecognized compensation expense related to the restricted stock units		700
Additional compensation expense as a result of meeting certain achievements		$ 300

Commitments and Contingencies -

Commitments and Contingencies - Rent Expense and Lease Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020USD ($)ft²	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Property, Plant and Equipment [Line Items]
Rent expense, including real estate taxes	$ 0.4	$ 0.3
Rent expense, including real estate taxes			$ 1.7
Vendor Financing Arrangement
Property, Plant and Equipment [Line Items]
Vendor financing arrangement, outstanding balance	$ 0.4
Exton Facility
Property, Plant and Equipment [Line Items]
Leased office space | ft²	11,000

Commitments and Contingencies_2

Commitments and Contingencies - Future Minimum Commitments Under Lease Agreements (Details) $ in Thousands	Dec. 31, 2020USD ($)
Commitments and Contingencies
2021	$ 244
2022	249
2023	250
2024	240
2025	101
Total future minimum lease commitments	$ 1,084

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Unrecognized tax benefits from uncertain tax	$ 0	$ 0	$ 0
Period over which material changes in unrecognized tax positions are not expected	12 months
Federal
Income Taxes
Cumulative net operating loss carryforwards	$ 328,700
Percentage of taxable income that can be used to offset future taxable periods as a result of the TCJA	80.00%
Unlimited carryforward	$ 131,300
Tax credit carryforwards	25,000
State
Income Taxes
Cumulative net operating loss carryforwards	323,200
Tax credit carryforwards	$ 1,900
State | Massachusetts
Income Taxes
Carryforward term	20 years
Potential amount that may expire in a future period	$ 23,400
State | Pennsylvania
Income Taxes
Carryforward term	20 years

Income Taxes - Components of th

Income Taxes - Components of the Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Income Taxes
Operating loss carryforwards	$ 90,895	$ 81,403
Tax credit carryforwards	26,550	23,072
Stock-based compensation	6,820	7,818
Lease liabilities	276	308
Other	162	176
Total deferred tax assets	124,703	112,777
Right-of-use asset	(270)	(306)
Valuation allowance	$ (124,433)	$ (112,471)

Income Taxes - Difference Betwe

Income Taxes - Difference Between U.S. Federal Corporate Tax Rate and Company's Effective Tax Rate (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Taxes
Expected federal income tax rate	(21.00%)	(21.00%)	(21.00%)
Expiring credits and NOLs			1.00%
Change in valuation allowance	10.60%	26.20%	37.90%
Federal and state credits	(3.10%)	(8.10%)	(7.40%)
State income taxes, net of federal benefit	(1.90%)	(4.70%)	(9.70%)
Warrant and future tranche right revaluation loss	14.20%	4.30%
Stock-based compensation	0.20%	0.50%	0.50%
Other	1.00%	2.80%	(1.30%)
Effective tax rate	0.00%	0.00%	0.00%

Employee Benefit Plan (Details)

Employee Benefit Plan (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Aug. 31, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Benefit Plan
Maximum employer match as a percentage of base pay	5.00%	3.00%
Percentage the employer matches of employee contributions	100.00%	50.00%
Portion of the employee's base salary that the Company matches	5.00%	6.00%
Employer matching contributions to the plan		$ 0.3	$ 0.3	$ 0.2

Related Party Transactions - Ov

Related Party Transactions - Overview of Related Parties (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended		12 Months Ended
	Dec. 31, 2020	Jan. 31, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Related Party Transactions
Exercise price of warrants	$ 1.28		$ 1.28	$ 0.75
Number of Warrants	16,967,828		16,967,828	5,098,916
Common stock issued in lieu of board fees			145,392	53,985	13,654
Restricted stock units
Related Party Transactions
Award granted			365,845
Restricted stock units | 2013 Stock Incentive Plan
Related Party Transactions
Award granted			128,170
Board of Director
Related Party Transactions
Ownership percentage	12.00%		12.00%
Aggregate common shares			4,608,786
Maximum
Related Party Transactions
Proceeds from issuance of common stock in lieu of director board and committee fees			$ 0.3	$ 0.1	$ 0.1
Baker Bros. Advisors LP
Related Party Transactions
Number of warrants exercised					2,700,791
Exercise price of warrants					$ 3.76
Proceeds from exercise of warrants					$ 9.5
Maximum beneficial ownership percentage holding, after convertible securities converted				4.99%
Prior notice period (in days)				61 days
Baker Bros. Advisors LP | Maximum
Related Party Transactions
Maximum beneficial ownership percentage holding, after convertible securities converted				19.99%
Baker Bros. Advisors LP | Pre-funded Warrants | Scenario One
Related Party Transactions
Exercise price of warrants	$ 0.08		$ 0.08
Baker Bros. Advisors LP | Pre-funded Warrants | Scenario One | Maximum
Related Party Transactions
Number of Warrants	2,708,812		2,708,812
Baker Bros. Advisors LP | Pre-funded Warrants | Scenario Two | Maximum
Related Party Transactions
Number of Shares	2,368,400		2,368,400
Baker Bros. Advisors LP | Series B1 Preferred Warrant | Scenario Two
Related Party Transactions
Exercise price of warrants	$ 152		$ 152
Baker Bros. Advisors LP | Preferred stock | Scenario Two
Related Party Transactions
Exercise price of warrants	$ 1.52		$ 1.52
Number of Warrants	23,684		23,684
Pillar Investment Entities
Related Party Transactions
Ownership percentage	18.00%		18.00%
Pillar Investment Entities | Pre-funded Warrants
Related Party Transactions
Exercise price of warrants		$ 0.01
Shares issued on exercise of warrants during the period		643,525
Pillar Investment Entities | Common Stock Warrants Exercise Price, Two Point Two Eight
Related Party Transactions
Exercise price of warrants	$ 2.28		$ 2.28
Number of Shares	3,039,514		3,039,514
Pillar Investment Entities | Common Stock Warrants Exercise Price Two Point Five Eight
Related Party Transactions
Exercise price of warrants	$ 2.58		$ 2.58
Number of Shares	2,764,227		2,764,227
Pillar Investment Entities | Pre Funded Warrant, Tranche One
Related Party Transactions
Exercise price of warrants	$ 0.01		$ 0.01
Number of Shares	2,014,234		2,014,234
Pillar Investment Entities | Common Stock Warrants Exercise Price Two Point Seven One
Related Party Transactions
Exercise price of warrants	$ 2.71		$ 2.71
Number of Shares	1,373,626		1,373,626
Pillar Investment Entities | Pre Funded Warrant, Tranche Two
Related Party Transactions
Exercise price of warrants	$ 0.01		$ 0.01
Number of Shares	2,677,311		2,677,311
Besancon
Related Party Transactions
Exercise price of warrants					$ 3.76
Proceeds from exercise of warrants					$ 0.6
Shares issued on exercise of warrants during the period					150,000
Chief Executive Officer | 2013 Stock Incentive Plan
Related Party Transactions
Award granted	128,170
Proceeds from issuance of restricted stock in lieu of salary	$ 0.6

Net Loss per Common Share App_3

Net Loss per Common Share Applicable to Common Stockholders - Antidilutive securities (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive securities
Total antidilutive securities	75,321	61,289	6,075
Stock options
Antidilutive securities
Total antidilutive securities	4,614	4,220	3,305
Restricted stock units
Antidilutive securities
Total antidilutive securities	903	194
Common Stock Warrants
Antidilutive securities
Total antidilutive securities	16,968	5,099	2,769
Convertible preferred stock
Antidilutive securities
Total antidilutive securities	2,369	2,369	1
Future tranche right liability
Antidilutive securities
Total antidilutive securities	50,467	49,407

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ in Millions	Feb. 28, 2021	Mar. 04, 2019	Feb. 28, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Subsequent Events
Net proceeds from offering of common stock			$ 16.3
"At-The-Market" Equity Program
Subsequent Events
Stock issued (in shares)				3,608,713	532,700
Net proceeds from offering of common stock						$ 0
Maximum value of shares that are permitted to be sold, subject to certain limitations				$ 35.4
Lincoln Park Capital Fund, LLC ("Investor")
Subsequent Events
Stock issued (in shares)		269,749		750,000	1,535,848
Net proceeds from offering of common stock				$ 1.7	$ 3.7
Maximum value of shares that are permitted to be sold, subject to certain limitations				$ 29.5
Subsequent Events | "At-The-Market" Equity Program
Subsequent Events
Stock issued (in shares)			2,394,956
Net proceeds from offering of common stock			$ 12.1
Maximum value of shares that are permitted to be sold, subject to certain limitations	$ 22.9
Subsequent Events | Lincoln Park Capital Fund, LLC ("Investor")
Subsequent Events
Stock issued (in shares)			800,000
Net proceeds from offering of common stock			$ 4.2
Maximum value of shares that are permitted to be sold, subject to certain limitations	$ 25.3