Endocyte (ECYT) 10-K 27 Feb 18 2017 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Feb. 23, 2018	Jun. 30, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Entity Registrant Name	ENDOCYTE INC
Entity Central Index Key	1,235,007
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Public Float			$ 57.2
Entity Common Stock, Shares Outstanding		48,349,930

CONDENSED BALANCE SHEETS

CONDENSED BALANCE SHEETS - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents at carrying value	$ 18,559,130	$ 31,228,192
Short-term investments	78,912,297	106,979,224
Receivables	273,044	55,074
Prepaid expenses	751,255	1,737,308
Other assets	77,077	255,912
Total current assets	98,572,803	140,255,710
Property and equipment, net	2,182,399	3,205,077
Other noncurrent assets	7,067	33,567
Total assets	100,762,269	143,494,354
Current liabilities:
Accounts payable	376,394	1,381,545
Accrued wages and benefits	2,533,133	2,705,475
Accrued clinical trial expenses	689,985	861,293
Accrued expenses and other liabilities	946,668	613,861
Total current liabilities	4,546,180	5,562,174
Other liabilities, net of current portion		2,873
Deferred revenue, net of current portion	731,944	781,944
Total liabilities	5,278,124	6,346,991
Stockholders’ equity:
Common stock: $0.001 par value, 100,000,000 shares authorized; 42,377,522 and 48,203,529 shares issued and outstanding at December 31, 2016 and December 31, 2017	48,204	42,378
Additional paid-in capital	404,454,909	390,768,742
Accumulated other comprehensive (loss) income	(64,433)	(41,196)
Retained deficit	(308,954,535)	(253,622,561)
Total stockholders’ equity	95,484,145	137,147,363
Total liabilities and stockholders’ equity	$ 100,762,269	$ 143,494,354

CONDENSED BALANCE SHEETS (Paren

CONDENSED BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	48,203,529	42,377,522
Common stock, shares outstanding	48,203,529	42,377,522

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenue:
Collaboration revenue	$ 70,000	$ 70,000	$ 70,000
Total revenue	70,000	70,000	70,000
Operating expenses:
Research and development	25,866,845	27,492,185	26,309,475
General and administrative	13,769,853	17,298,139	15,733,462
Acquired in-process research and development	16,539,347	0	0
Total operating expenses	56,176,045	44,790,324	42,042,937
Loss from operations	(56,106,045)	(44,720,324)	(41,972,937)
Other income (expense), net:
Interest income, net	1,029,497	861,212	651,543
Other income (expense), net	12,398	(28,461)	51,645
Net loss	$ (55,064,150)	$ (43,887,573)	$ (41,269,749)
Net loss per share -basic and diluted (in dollars per share)	$ (1.25)	$ (1.04)	$ (0.98)
Items included in other comprehensive income (loss):
Unrealized gain on foreign currency translation			$ 50,592
Unrealized gain (loss) and amounts reclassified to net loss on available-for-sale securities	$ (23,237)	$ 38,203	13,937
Other comprehensive income (loss)	(23,237)	38,203	64,529
Comprehensive loss	$ (55,087,387)	$ (43,849,370)	$ (41,205,220)
Weighted-average number of common shares used in net loss per share calculation - basic and diluted (in shares)	43,900,257	42,210,643	41,939,504

CONDENSED STATEMENT OF STOCKHOL

CONDENSED STATEMENT OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($)	New Accounting Pronouncement Early Adoption EffectAdditional Paid-in Capital	New Accounting Pronouncement Early Adoption EffectRetained Deficit	New Accounting Pronouncement Early Adoption Effect	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Retained Deficit	Total
Balance at beginning of period at Dec. 31, 2014				$ 41,785	$ 373,571,500	$ (143,928)	$ (168,465,239)	$ 205,004,118
Balances (in shares) at Dec. 31, 2014				41,784,692
Exercise of stock options				$ 146	379,144	0	0	$ 379,290
Exercise of stock options (in shares)				146,046				146,046
Stock-based compensation				$ 29	6,862,917			$ 6,862,946
Stock-based compensation (in shares)				29,190
Employee stock purchase plan				$ 75	304,928	0	0	305,003
Number of shares purchased under ESPP				74,805
Net loss				$ 0	0	0	(41,269,749)	(41,269,749)
Net realized loss on foreign exchange translation				0	0	50,592	0	50,592
Unrealized gain (loss) on securities				0	0	13,937	0	13,937
Balance at end of period at Dec. 31, 2015				$ 42,035	381,118,489	(79,399)	(209,734,988)	171,346,137
Balances (in shares) at Dec. 31, 2015				42,034,733
Balance after adjustment (in shares)				42,377,522
Exercise of stock options				$ 130	260,952	0	0	$ 261,082
Exercise of stock options (in shares)				129,638				129,638
Stock-based compensation				$ 127	9,157,528	0	0	$ 9,157,655
Stock-based compensation (in shares)				126,580
Employee stock purchase plan				$ 86	231,773	0	0	231,859
Number of shares purchased under ESPP				86,571
Net loss				$ 0	0	0	(43,887,573)	(43,887,573)
Unrealized gain (loss) on securities				0	0	38,203	0	38,203
Balance at end of period at Dec. 31, 2016				$ 42,378	390,768,742	(41,196)	(253,622,561)	137,147,363
Balances (in shares) at Dec. 31, 2016				42,377,522
Reclassification of impact of ASU 2016-09 (See Note 3) | ASU 2016-09	$ 267,824	$ (267,824)	$ 0
Balance after adjustment				$ 42,378	391,036,566	(41,196)	(253,890,385)	137,147,363
Exercise of stock options				$ 378	1,087,513			$ 1,087,891
Exercise of stock options (in shares)				378,030				378,030
Stock-based compensation				$ 114	4,075,903			$ 4,076,017
Stock-based compensation (in shares)				114,365
Employee stock purchase plan				$ 56	72,056			72,112
Issuance of common stock in connection with development and license agreement				$ 2,000	2,818,000			2,820,000
Issuance of common stock in connection with development and license agreement (in shares)				2,000,000
Issuance of common stock in connection with exercise of warrant to purchase common stock				$ 3,278	5,364,871			5,368,149
Issuance of common stock in connection with exercise of warrant to purchase common stock (in shares)				3,278,000
Number of shares purchased under ESPP				55,612
Net loss							(55,064,150)	(55,064,150)
Unrealized gain (loss) on securities				$ 0	0	(23,237)	0	(23,237)
Balance at end of period at Dec. 31, 2017				$ 48,204	$ 404,454,909	$ (64,433)	$ (308,954,535)	$ 95,484,145
Balances (in shares) at Dec. 31, 2017				48,203,529

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net income (loss)	$ (55,064,150)	$ (43,887,573)	$ (41,269,749)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	922,670	919,809	886,710
Stock-based compensation	4,170,645	9,322,127	6,920,220
Acquired in-process research and development	16,539,347	0	0
Loss on disposal of property and equipment	106,217	0	10,639
Accretion of bond premium (discount)	(161,399)	395,116	1,310,238
Net realized foreign currency translation loss	0	0	51,944
Change in operating assets and liabilities:
Receivables	1,433	191,555	856,372
Prepaid expenses and other assets	915,499	(517,318)	(96,582)
Accounts payable	(1,025,199)	(252,605)	(60,713)
Accrued wages, benefits and other liabilities	(13,717)	(771,866)	(777,204)
Deferred revenue	(50,000)	(50,000)	(50,000)
Net cash used in operating activities	(33,658,654)	(34,650,755)	(32,218,125)
Investing activities
Purchases of property and equipment	(82,455)	(713,839)	(341,616)
Proceeds from disposal of property and equipment	15,727	0	0
Purchases of investments	(106,724,911)	(139,932,358)	(86,281,946)
Purchase of acquired in-process research and development	(12,770,565)	0	0
Proceeds from sale and maturities of investments	134,930,000	190,765,053	88,114,199
Net cash provided by investing activities	15,367,796	50,118,856	1,490,637
Financing activities
Stock repurchase	(94,628)	(164,472)	(57,274)
Proceeds from exercise of warrant to purchase common stock	4,556,421	0	0
Proceeds from the exercise of stock options	1,087,891	261,082	379,290
Proceeds from stock purchases under employee stock purchase plan	72,112	231,859	305,003
Net cash provided by financing activities	5,621,796	328,469	627,019
Effect of exchange rate	0	0	(1,352)
Net increase (decrease) in cash and cash equivalents	(12,669,062)	15,796,570	(30,101,821)
Cash and cash equivalents at beginning of period	31,228,192	15,431,622	45,533,443
Cash and cash equivalents at end of period	$ 18,559,130	$ 31,228,192	$ 15,431,622

Nature of Business and Organiza

Nature of Business and Organization	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Business and Organization	1. Nature of Business and Organiz Endocyte, Inc. (the “Company”) is a biopharmaceutical company and leader in developing targeted therapies for the treatment of cancer. The Company uses drug conjugation technology to create novel therapeutics and companion imaging agents for personalized targeted therapies. The agents actively target receptors that are over-expressed on diseased cells relative to healthy cells, such as prostate specific membrane antigen (“PSMA”) in prostate cancer. This targeted approach is designed to safely enable the delivery of highly potent drug payloads. The companion imaging agents are designed to identify patients whose disease over-expresses the target of the therapy and who are therefore more likely to benefit from treatment. In June 2017, the Company discontinued clinical development of EC1456 and stopped enrollment in its EC1456 phase 1b trial as the assessment of trial data did not yield the level of clinical activity necessary to support continued advancement of EC1456. In December 2017, the Company stopped enrollment in its EC1456 ovarian cancer surgical trial. In addition, in June 2017, the Company narrowed the focus of its phase 1 clinical development of EC1169 to include only the cohort of taxane-exposed metastatic castration-resistant prostate cancer (“mCRPC”) patients, which completed enrollment in October 2017. The Company does not intend to invest further resources in the development of EC1169 beyond the completion of the phase 1 taxane-exposed cohort. In addition, in June 2017, the Company reduced its workforce by approximately 40% to align resources to focus on the Company’s highest value opportunities while maintaining key capabilities. In September 2017, the Company entered into a Development and License Agreement (the “License Agreement”) with ABX advanced biochemical compounds – Biomedizinische Forschungsreagenzien GmbH (“ABX”), pursuant to which the Company acquired exclusive worldwide rights to develop and commercialize PSMA-617 agents, including the product candidate known as 177 Lu-PSMA-617, a radioligand therapeutic (“RLT”). Following a successful End of Phase 2 meeting with the U.S. Food and Drug Administration (“FDA”), the Company finalized the phase 3 VISION trial design and registration plan for 177 Lu-PSMA-617. The trial will include two interim assessments of efficacy, which could potentially lead to an early approval for 177 Lu-PSMA-617. The Company intends to initiate, in the second quarter of 2018, the VISION trial, an international, prospective, open-label, multicenter, randomized phase 3 study of 177 Lu-PSMA-617 in up to 750 patients with progressive PSMA-positive mCRPC who have received at least one novel androgen axis drug (NAAD) and at least one taxane regimen. On October 2, 2017, the Company announced its plan to primarily focus its resources on the development of 177 Lu-PSMA‑617 and on a targeted effort to generate proof-of-concept data for the adaptor-controlled CAR T-cell program, and to explore out-licensing opportunities for all other development programs, such as EC2629. The Company had two wholly-owned subsidiaries, Endocyte Europe B.V. and Endocyte Europe GmbH, which were formed to assist with the administration of applications with the European Commission (“EC”) and commercial pre-launch activities in Europe. The applications were withdrawn in May 2014 and the commercial pre-launch activities in Europe ceased. The Company dissolved Endocyte Europe GmbH in the fourth quarter of 2015 and dissolved Endocyte Europe B.V. in the first quarter of 2016.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Significant Accounting Policies	2. Significant Accounting Policies Basis of Presentation The accompanying consolidated financial statements include the accounts of Endocyte, Inc. and its subsidiaries and all intercompany amounts have been eliminated as of December 31, 2015. The accompanying financial statements for the years ended December 31, 2016 and 2017 include only the accounts of Endocyte, Inc. as the Company dissolved Endocyte Europe GmbH and Endocyte Europe B.V. in the fourth quarter of 2015 and the first quarter of 2016, respectively. There were no intercompany transactions in the years ended December 31, 2016 or 2017 and no intercompany balances as of December 31, 2016 or 2017. The consolidated financial statements are prepared in conformity with U.S. generally accepted accounting principles (“GAAP”) for annual financial information to Form 10-K. Subsequent events have been evaluated through the date of issuance, which is the same as the date this Form 10-K is filed with the Securities and Exchange Commission (the “SEC”). Use of Estimates The preparation of financial statements in conformity with GAAP requires the Company’s management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual amounts may differ from those estimates. Cash and Cash Equivalents The Company considers cash and all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. Cash equivalents consist primarily of money market instruments, U.S. government treasury obligations, corporate debt securities and repurchase agreements that are maintained by an investment manager. Investments Investments consist primarily of investments in U.S. Treasuries and corporate debt securities, which could also include commercial paper, that are maintained by an investment manager. Management determines the appropriate classification of marketable securities at the time of purchase and reevaluates such classification as of each balance sheet date. Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in other comprehensive income. Realized gains and losses and declines in value judged to be other-than-temporary on available-for-sale securities are included in other income. The Company considers and accounts for other-than-temporary impairments according to the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 320, Investments — Debt and Equity Securities (“ASC 320”). The cost of securities sold is based on the specific-identification method. Discounts and premiums on debt securities are amortized to interest income and expensed over the term of the security. Property and Equipment Property and equipment are stated at cost and are being depreciated using the straight-line method over estimated useful lives, which range from three to seven years. Licenses and Patents Licenses and patent costs are expensed as incurred as the Company does not believe there is an alternate future use for the costs. Licenses are classified as research and development expenses and patents are classified as general and administrative expenses in the consolidated statements of operations. Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment when events or changes in business conditions indicate that their full carrying value may not be fully recoverable. Leases The Company evaluates all leases to determine whether they should be accounted for as operating or capital leases. Revenue Recognition The Company recognizes revenues from license and collaboration agreements when persuasive evidence of an arrangement exists, delivery has occurred or services have been rendered, the fee is fixed or determinable, and there is reasonable assurance that the related amounts are collectible in accordance with ASC Topic 605, Revenue Recognition (“ASC 605”). The Company’s license and collaboration agreements may contain multiple elements, including grants of licenses to intellectual property rights, agreement to provide research and development services and other deliverables. The deliverables under such arrangements are evaluated under ASC Subtopic 605-25, Multiple-Element Arrangements (“ASC 605-25”). Under ASC 605-25, each required deliverable is evaluated to determine whether it qualifies as a separate unit of accounting based on whether the deliverable has “stand-alone value” to the customer. The arrangement’s consideration that is fixed or determinable, excluding contingent milestone payments and royalties, is then allocated to each separate unit of accounting based on the relative selling price of each deliverable. In general, the consideration allocated to each unit of accounting is recognized as the related goods or services are delivered, limited to the consideration that is not contingent upon future deliverables. Upfront payments for licensing the Company’s intellectual property are evaluated to determine if the licensee can obtain stand-alone value from the license separate from the value of the research and development services and other deliverables in the arrangement to be provided by the Company. If at the inception of an arrangement the Company determines that the license does not have stand-alone value separate from the research and development services or other deliverables, the license, services and other deliverables are combined as one unit of account and upfront payments are recorded as deferred revenue on the balance sheet and are recognized in a manner consistent with the final deliverable. Subsequent to the inception of an arrangement, the Company evaluates the remaining deliverables for separation as items in the arrangement are delivered. When stand-alone value is identified, the related consideration is recorded as revenue in the period in which the license or other intellectual property rights are delivered. In those circumstances where research and development services or other deliverables are combined with the license, and multiple services are being performed such that a common output measure to determine a pattern of performance cannot be discerned, the Company recognizes amounts received on a straight line basis over the performance period. Such amounts are recorded as collaboration revenue. Any subsequent reimbursement payments, which are contingent upon the Company’s future research and development expenditures, will be recorded as collaboration revenue and will be recognized on a straight-line basis over the performance period using the cumulative catch up method. The costs associated with these activities are reflected as a component of research and development expense in the statements of operations in the period incurred. In the event of an early termination of a collaboration agreement, any deferred revenue is recognized in the period in which all obligations of the Company under the agreement have been fulfilled. Milestone payments under collaborative arrangements are triggered either by the results of the Company’s research and development efforts, achievement of regulatory goals or by specified sales results by a third-party collaborator. Milestones related to the Company’s development-based activities may include initiation of various phases of clinical trials and applications and acceptance for product approvals by regulatory agencies. Due to the uncertainty involved in meeting these development-based milestones, the determination is made at the inception of the collaboration agreement whether the development-based milestones are considered to be substantive (i.e. not just achieved through passage of time). In addition, the amounts of the payments assigned thereto are considered to be commensurate with the enhancement of the value of the delivered intellectual property as a result of the Company’s performance. Because the Company’s involvement is necessary to the achievement of development-based milestones, the Company would account for development-based milestones as revenue upon achievement of the substantive milestone events. Milestones related to sales-based activities may be triggered upon events such as first commercial sale of a product or when sales first achieve a defined level. Since these sales-based milestones would be achieved after the completion of the Company’s development activities, the Company would account for the sales-based milestones in the same manner as royalties, with revenue recognized upon achievement of the milestone. Royalties based on reported sales of licensed products will be recognized based on contract terms when reported sales are reliably measurable and collectability is reasonably assured. To date, none of the Company’s products have been approved and therefore the Company has not earned any royalty revenue from product sales. In territories where the Company and a collaborator may share profit, the revenue would be recorded in the period earned. The Company often is required to make estimates regarding drug development and commercialization timelines for compounds being developed pursuant to a collaboration agreement. Because the drug development process is lengthy and the Company’s collaboration agreements typically cover activities over several years, this approach often results in the deferral of significant amounts of revenue into future periods. In addition, because of the many risks and uncertainties associated with the development of drug candidates, the Company’s estimates regarding the period of performance may change in the future. Any change in the Company’s estimates or a termination of the arrangement could result in substantial changes to the period over which the revenues are recognized. Research and Development Expenses Research and development expenses represent costs associated with the ongoing development of novel therapeutics and companion imaging agents for personalized targeted therapies and include salaries and employee benefits, supplies, facility costs related to research activities, and expenses for clinical trials. The Company records accruals for clinical trial expenses based on the estimated amount of work completed. The Company monitors patient enrollment levels and related activities to the extent possible through internal reviews, correspondence, and discussions with research organizations. In the event that a clinical trial is terminated early, the Company records, in the period of termination, an accrual for the estimated remaining costs to complete and close out the trial pursuant to ASC Topic 420, Exit or Disposal Cost Obligations , as a terminated trial does not provide any future economic benefit to the Company. See Note 15 – Restructuring Costs of the Notes to Consolidated Financial Statements contained herein for costs incurred during the years ended December 31, 2015, 2016, and 2017 related to the Company’s restructuring activities. Upfront payments made in connection with business collaborations and research and development arrangements are evaluated under ASC Subtopic 730-20, Research and Development Arrangements . Amounts related to future research and development are capitalized as prepaid research and development and are expensed over the service period based upon the level of services provided. As of December 31, 2017, the Company had approximately $0.1 million of capitalized research and development costs included in prepaid expenses. Acquired In-Process Research and Development Expense The Company has acquired and may continue to acquire the rights to develop and commercialize new drug candidates. In accordance with ASC Subtopic 730-25, Accounting for Research and Development Costs, the upfront payments to acquire a new drug compound, as well as future milestone payments when paid or payable, are immediately expensed as acquired in-process research and development (“IPR&D”) in transactions other than a business combination provided that the drug has not achieved regulatory approval for marketing and, absent obtaining such approval, has no alternative future use. Upon obtaining regulatory approval for marketing, any related milestone payments may be capitalized and amortized over the life of the asset. Stock-Based Compensation The Company accounts for its stock-based compensation pursuant to ASC Topic 718, Compensation — Stock Compensation (“ASC 718”), which requires the recognition of the fair value of stock-based compensation in net income. Stock-based compensation consists of stock options, which are granted at exercise prices at or above the fair market value of the Company’s common stock on the dates of grant, service-based restricted stock units (“RSUs”), performance-based RSUs (“PRSUs”), and shares available for purchase under the Company’s 2010 Employee Stock Purchase Plan (“ESPP”). For PRSUs issued by the Company, stock-based compensation expense would be recognized if and when the Company determines that it is probable that the performance conditions will be achieved. For RSUs and stock options issued by the Company, stock-based compensation expense is recognized ratably over the service period. The Company recognizes compensation cost based on the grant-date fair value estimated in accordance with the provisions of ASC 718. Net Loss Per Share The Company calculates basic net loss per share based on the weighted-average number of outstanding common shares. The Company calculates diluted net loss per share based on the weighted-average number of outstanding common shares plus the effect of dilutive securities. Income Taxes The Company accounts for income taxes under the liability method in accordance with the provision of ASC Topic 740, Income Taxes (“ASC 740”). ASC 740 requires recognition of deferred taxes to provide for temporary differences between financial reporting and tax basis of assets and liabilities. Deferred taxes are measured using enacted tax rates expected to be in effect in a year in which the basis difference is expected to reverse. The Company continues to record a valuation allowance for the full amount of deferred tax assets, which would otherwise be recorded for tax benefits relating to operating loss and tax credit carryforwards, as realization of such deferred tax assets cannot be determined to be more likely than not. The Company accounts for uncertain income tax positions recognized in the financial statements in accordance with Accounting Standards Update (“ASU”) No. 2009-06. This guidance prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return and provides guidance on derecognition of tax benefits, classification on the balance sheet, interest and penalties, accounting in interim periods, disclosure, and transition. Segment Information Operating segments are defined as components of an enterprise engaging in business activities for which discrete financial information is available and regularly reviewed by the chief operating decision maker in deciding how to allocate resources and in assessing performance. The Company had performed clinical trials globally and established a subsidiary in The Netherlands to assist in the administration of filing applications in Europe and a subsidiary in Switzerland for commercial pre-launch activities in Europe. The applications filed in Europe were withdrawn in May 2014 and the pre-launch activities in Europe ceased. The Company dissolved Endocyte Europe GmbH in the fourth quarter of 2015 and dissolved Endocyte Europe B.V. in the first quarter of 2016. All long-lived assets are held in the U.S. The Company views its operations and manages its business in one operating segment.

New Accounting Pronouncements

New Accounting Pronouncements	12 Months Ended
	Dec. 31, 2017
Accounting Changes and Error Corrections [Abstract]
New Accounting Pronouncements	3. New Accounting Pronouncements Recently Issued Accounting Standards In January 2017, the FASB issued ASU 2017-01, Clarifying the Definition of a Business, an update to ASC Topic 805, Business Combinations . This guidance is intended to clarify the definition of a business as it relates to the evaluation of whether a set of transferred assets and activities are accounted for as a business combination or as an asset acquisition. This update was effective for the Company in the year ended December 31, 2017, as the Company elected early adoption. As a result, the Company considered ASU 2017-01 when evaluating the License Agreement. In the year ended December 31, 2017, the Company determined that the set of transferred assets and activities included in the License Agreement did not meet the definition of a business and accounted for the License Agreement as an asset acquisition. The adoption of this guidance did not have a material impact on the Company’s financial statements. In March 2016, the FASB issued ASU 2016-09, Improvements to Employee Share-Based Payment Accounting , an update to ASC Topic 718, Stock Compensation . This guidance involves improving several aspects of the accounting for share-based payment transactions, including classification of awards as either equity or liabilities, classification on the statement of cash flows, the method of accounting for forfeitures and requiring entities to recognize all income tax effects of awards in the income statement when the awards vest or are settled. This update was effective for the Company for interim and annual reporting periods beginning January 1, 2017. In the year ended December 31, 2017, the Company adopted this guidance using the modified retrospective method. As a result, the Company has elected to account for forfeitures as they occur and no longer estimates the number of awards expected to be forfeited. The cumulative effect related to the change in accounting for forfeitures was a $0.3 million increase to the opening balance of retained deficit at January 1, 2017. Additionally, as a result of the adoption, the Company recognized the excess tax benefits of awards that have vested or settled that had previously not been recognized as the related tax deduction had increased the Company’s net operating loss carryforward. The Company determined, consistent with its accounting for existing net operating losses, that a full valuation allowance was required for the excess tax benefits. As such, the Company recognized an increase in its net operating loss carryforward deferred tax asset of $0.8 million and the valuation allowance against the net operating loss carryforward was also increased by $0.8 million, which resulted in no impact to the financial statements. The adoption of this guidance did not have a material impact on the Company’s financial statements. In February 2016, the FASB issued ASU 2016-02, Leases , an update to ASC Topic 842, Leases . This guidance requires lessees to recognize leases as assets and liabilities on their balance sheets but recognize expenses on their income statements in a manner similar to the current accounting guidance. For lessors, the guidance also modifies the classification criteria and the accounting for sales-type and direct finance leases. This update is effective for the Company for interim and annual reporting periods beginning January 1, 2019 unless it elects early adoption. The Company is currently evaluating the impact, if any, the adoption of this guidance will have on its consolidated financial statements. In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606), to clarify the principles used to recognize revenue for all entities. Under ASU 2014-09, an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In order to do so, an entity would follow the five-step process for in-scope transactions: 1) identify the contract with a customer, 2) identify the separate performance obligations in the contract, 3) determine the transaction price, 4) allocate the transaction price to the separate performance obligations in the contract, and 5) recognize revenue when (or as) the entity satisfies a performance obligation. In August 2015, the FASB issued ASU 2015-14, which defers the effective date of ASU 2014-09 by one year. Therefore, ASU 2014-09 will become effective for the Company for interim and annual reporting periods beginning after December 15, 2017. Early adoption is permitted, but not any earlier than the original effective date of December 15, 2016. An entity can apply the new revenue standard retrospectively to each prior reporting period presented or retrospectively with the cumulative effect of initially applying the standard recognized at the date of initial application in retained earnings. In April 2016, the FASB issued ASU 2016-10, an update to Topic 606, which clarifies how entities should identify performance obligations and evaluate licensing. In May 2016, the FASB issued ASU 2016-12, an update to Topic 606, which clarifies guidance on transition, collectability, noncash consideration and the presentation of sales and other similar taxes. In December 2016, the FASB issued ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers, which affects narrow aspects of the guidance issued in ASU 2014-09. The Company currently has a limited number of contracts with customers and only one revenue stream, which relates to collaboration and licensing arrangements, and which represents all of the revenue earned in the year ended December 31, 2017. The Company will adopt the new standard effective January 1, 2018. The Company has identified all of its contracts and has completed a preliminary review of the estimated impact of the adoption of this ASU, which is not expected to have a material impact on the Company’s consolidated financial statements.

Net Loss per Share

Net Loss per Share	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	4. Net Loss per Share Basic net loss per share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury-stock method and the if-converted method. For purposes of this calculation, stock options, warrants, PRSUs, RSUs and shares to be purchased under the ESPP are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. Common stock equivalents As of December 31, 2015, 2016, and 2017 the following number of potential common stock equivalents were outstanding: Year Ended December 31, 2015 2016 2017 Outstanding common stock options 5,686,815 6,447,594 5,878,660 Outstanding warrants 34,647 34,647 722,000 Outstanding PRSUs 213,758 — — Outstanding RSUs 351,414 394,132 1,383,770 Shares to be purchased under the ESPP 4,236 4,394 2,634 Total 6,290,870 6,880,767 7,987,064 These common stock equivalents were excluded from the determination of diluted net loss per share due to their anti-dilutive effect on earnings. The increase in warrants was due to warrants issued in connection with the License Agreement. For additional information on the outstanding warrants, see Note 8 – Warrants of the Notes to Consolidated Financial Statements contained herein.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2017
Stockholders' Equity Note [Abstract]
Other Comprehensive Income (Loss)	5. Other Comprehensive Income (Loss) The accumulated balances related to each component of other comprehensive income (loss) were as follows: Foreign Accumulated Currency Unrealized Net Other Translation Gains (Losses) Comprehensive Gains (Losses) on Securities Gains (Losses) Balance at December 31, 2014 $ (50,592) $ (93,336) $ (143,928) Unrealized gain (loss) (1,352) 18,841 17,489 Net amount reclassified to net loss 51,944 (4,904) 47,040 Other comprehensive income 50,592 13,937 64,529 Balance at December 31, 2015 $ — $ (79,399) $ (79,399) Unrealized gain — 36,908 36,908 Net amount reclassified to net loss — 1,295 1,295 Other comprehensive income — 38,203 38,203 Balance at December 31, 2016 $ — $ (41,196) $ (41,196) Unrealized loss — (23,237) (23,237) Other comprehensive loss — (23,237) (23,237) Balance at December 31, 2017 $ — $ (64,433) $ (64,433) The assets and liabilities of foreign operations were translated into U.S. dollars using the current exchange rate. For those operations, changes in exchange rates generally did not affect cash flows, which resulted in translation adjustments made in stockholders’ equity rather than to net loss. The accumulated balance of translation adjustments for Endocyte Europe B.V. were reclassified out of accumulated other comprehensive income (loss) and recognized as foreign currency translation losses reported in other income (expense) as the Company determined that the liquidation of Endocyte Europe B.V. was substantially complete as of December 31, 2015. There were no transactions from foreign operations in the years ended December 31, 2016 or 2017. Reclassifications Out of Accumulated Other Comprehensive Income (Loss) Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Year Ended Year Ended Year Ended Consolidated Details about Accumulated Other December 31, December 31, December 31, Statements of Operations and Comprehensive Income (Loss) Components 2015 2016 2017 Comprehensive Income (Loss) Unrealized Net Gains (Losses) on Securities $ (4,904) $ 1,295 $ — Other income (expense) Foreign Currency Translation Losses 51,944 — — Other income (expense) Total Reclassifications for the Period $ 47,040 $ 1,295 $ —

Investments

Investments	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Investments	6. Investments The Company applies the fair value measurement and disclosure provisions of ASC Topic 820, Fair Value Measurements and Disclosures (“ASC 820”). ASC 820, which defines fair value, establishes a framework for measuring fair value in GAAP, and expands disclosures about fair value measurements. Investments consist primarily of investments with original maturities greater than three months, but no longer than 24 months when purchased. ASC 820 establishes a three-level valuation hierarchy for fair value measurements. These valuation techniques are based upon the transparency of inputs (observable and unobservable) to the valuation of an asset or liability as of the measurement date. Observable inputs reflect market data obtained from independent sources, while unobservable inputs reflect the Company’s market assumptions. These two types of inputs create the following fair value hierarchy: Level 1 — Valuation is based on quoted prices for identical assets or liabilities in active markets. Level 2 — Valuation is based on quoted prices for similar assets or liabilities in active markets, or other inputs that are observable for the asset or liability, either directly or indirectly, for the full term of the financial instrument. Level 3 — Valuation is based upon other unobservable inputs that are significant to the fair value measurement. The fair value of the Company’s fixed income securities is based on a market approach using quoted market values. The following table summarizes the fair value of cash and cash equivalents and investments as of December 31, 2016: Fair Value Description Cost Level 1 Level 2 (Carrying Value) Cash Cash $ 6,249,703 $ 6,249,703 $ — $ 6,249,703 Cash equivalents (original maturity of 3 months or less) FDIC insured deposits and money market funds 24,978,489 24,978,489 — 24,978,489 Cash and cash equivalents $ 31,228,192 $ 31,228,192 $ — $ 31,228,192 Short-term investments (due within 1 year) U.S. government treasury obligations $ 86,078,622 $ 86,053,755 $ — $ 86,053,755 Corporate obligations 20,941,799 — 20,925,469 20,925,469 Total short-term investments $ 107,020,420 $ 86,053,755 $ 20,925,469 $ 106,979,224 The following table summarizes the fair value of cash and cash equivalents and investments as of December 31, 2017: Fair Value Description Cost Level 1 Level 2 (Carrying Value) Cash Cash $ 2,544,972 $ 2,544,972 $ — $ 2,544,972 Cash equivalents (original maturity of 3 months or less) Repurchase agreements 10,000,000 — 10,000,000 10,000,000 Money market funds 6,014,158 6,014,158 — 6,014,158 Cash and cash equivalents $ 18,559,130 $ 8,559,130 $ 10,000,000 $ 18,559,130 Short-term investments (due within 1 year) U.S. government treasury obligations $ 63,034,548 $ 62,970,115 $ — $ 62,970,115 Corporate obligations 15,942,182 — 15,942,182 15,942,182 Total short-term investments $ 78,976,730 $ 62,970,115 $ 15,942,182 $ 78,912,297 All securities held at December 31, 2016 and 2017, were classified as available-for-sale as defined by ASC 320. Total unrealized gross gains were $8,257 for the year ended December 31, 2016. There were no unrealized gross gains for the year ended December 31, 2017. Total unrealized gross losses were $49,453 and $64,433 for the years ended December 31, 2016 and 2017, respectively. The Company does not consider any of the unrealized losses to be other-than-temporary impairments because the Company has the intent and ability to hold investments until they recover in value. There were no total realized gross gains for the year ended December 31, 2016 or 2017. Total realized gross losses were $53 for the year ended December 31, 2016. There were no total realized gross losses for the year ended December 31, 2017.

Property and Equipment

Property and Equipment	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment Disclosure [Text Block]	7. Property and Equipment Property and equipment consisted of the following: Estimated December 31, Useful Lives 2016 2017 Laboratory equipment 7 $ 6,666,506 $ 5,626,280 Office equipment and software 3 – 7 1,347,768 1,245,232 Leasehold improvements 7 424,176 424,176 Assets not in service 19,000 66,809 8,457,450 7,362,497 Less accumulated depreciation (5,252,373) (5,180,098) $ 3,205,077 $ 2,182,399 Assets not in service represent new laboratory equipment, computer equipment and software that were not installed and ready to use at December 31, 2016 and excess equipment held for sale at December 31, 2017. The total amount of depreciation expense for the years ended December 31, 2015, 2016 and 2017 were $886,710, $919,809 and $922,670 respectively.

Warrants

Warrants	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Warrant Disclosure [Text Block]	8. Warrants In connection with the License Agreement, the Company issued to ABX on September 29, 2017, two warrants to purchase up to 4,000,000 shares of the Company’s common stock, at a per share exercise price of $1.39, which is equal to the average closing price of the Company’s common stock during the 30 calendar days prior to September 29, 2017. The Company accounted for the warrants at fair value in stockholders’ equity. The warrants contain a conversion feature in the case of certain mergers or consolidations by the Company. Immediately upon issuance, ABX assigned the warrants to an affiliate and certain related parties, which exercised a warrant for 3,278,000 shares on September 29, 2017, resulting in proceeds to the Company in the amount of approximately $4.6 million. The remaining warrant, covering an aggregate of 722,000 shares, remained outstanding as of December 31, 2017, is exercisable until September 29, 2027, and is subject to restrictions on transfer. This warrant was valued using the Black-Scholes model utilizing a ten-year term, the Company’s historic volatility of 91.1%, and an interest rate of 2.28% which is the risk free interest rate of a treasury bond with the same term as the warrants, which are level 2 fair value measurements. There were no other outstanding warrants as of December 31, 2017.

Leases

Leases	12 Months Ended
	Dec. 31, 2017
Leases [Abstract]
Leases of Lessee Disclosure [Text Block]	9. Leases Future minimum lease payments for noncancellable operating leases as of December 31, 2017, are as follows: 2018 $ 304,523 2019 — 2020 — 2021 — 2022 — Thereafter — Total minimum lease payments $ 304,523 Rent expense for operating leases was $736,249, $743,323 and $749,406 for the years ended December 31, 2015, 2016 and 2017, respectively.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Stockholders' Equity (Deficit)	10. Stockholders’ Equity Issuances Related to the License Agreement In connection with the License Agreement, the Company issued to ABX on September 29, 2017, 2,000,000 unregistered shares of the Company’s common stock and two warrants to purchase up to 4,000,000 shares of the Company’s common stock, one of which warrants to purchase 3,278,000 shares was exercised on that same day. Pursuant to a Registration Rights Agreement entered into with ABX, the Company registered for resale these 6,000,000 shares of common stock with the SEC on a Form S-3 Registration Statement that was declared effective on October 24, 2017. Stock-Based Compensation Plans The Company has had stock-based compensation plans since 1997. The awards made under the plans adopted in 1997 and 2007 consisted of stock options. The 2010 Equity Incentive Plan (the “2010 Plan”), which is the only plan under which awards may currently be made, authorizes awards in the form of stock options, stock appreciation rights, restricted stock, RSUs, PRSUs, and performance units and performance shares. Awards under the 2010 Plan may be made to employees, directors and certain consultants as determined by the compensation committee of the board of directors. There were 11,003,563 and 11,850,563 shares of common stock authorized and reserved under these plans at December 31, 2016 and December 31, 2017, respectively. Stock Options Under the various plans, employees have been granted incentive stock options, while directors and consultants have been granted non-qualified options. The plans allow the holder of an option to purchase common stock at the exercise price, which was at or above the fair value of the Company’s common stock on the date of grant. Generally, options granted under the 1997 and 2007 plans in connection with an employee’s commencement of employment vested over a four-year period with one-half of the shares subject to the grant vesting after two years of employment and the remaining options vesting monthly over the remainder of the four-year period. Options granted under the 1997 and 2007 plans for performance or promotions vested monthly over a four-year period. Generally, options granted under the 2010 Plan vest annually over a three-year or four-year period. Unexercised stock options terminate on the tenth anniversary date after the date of grant. The Company recognizes stock-based compensation expense over the requisite service period of the individual grantees, which generally equals the vesting period. The Company utilizes a Black-Scholes option-pricing model to estimate the value of stock options. The Black-Scholes model allows the use of a range of assumptions related to volatility, risk-free interest rate, employee exercise behavior and dividend yield. Expected volatilities used in the model beginning in 2015 are based on historical volatility of the Company’s stock prices. The Company is using the “simplified” method for “plain vanilla” options to estimate the expected term of the stock option grants. Under this approach, the weighted-average expected life is presumed to be the average of the vesting term and the contractual term of the option. The risk-free interest rate assumption is derived from the weighted-average yield of a U.S. Treasury security with the same term as the expected life of the options, and the dividend yield assumption is based on historical experience and the Company’s estimate of future dividend yields. The weighted-average value of the individual options granted during 2015, 2016 and 2017 were determined using the following assumptions: Year Ended December 31, 2015 2016 2017 Expected volatility 106.38 % 98.83 % 92.98 % Risk-free interest rate 1.55 % 1.47 % 2.15 % Weighted-average expected life (in years) 6.4 6.6 6.9 Dividend yield % % 0.00 % The resulting value of options granted was $2,838,053 and $1,600,031 for the years ended December 31, 2016 and 2017, respectively, which will be amortized into income over the remaining requisite service period. The Company executed a Separation Agreement and Release of Claims with its former Chief Executive Officer, P. Ron Ellis, in connection with his resignation from the Company in June 2016. Under this agreement and Mr. Ellis’ original Severance Agreement, the Company incurred additional stock-based compensation expense of $2,800,000 related to the modification of Mr. Ellis’ options and RSUs. The vesting of each stock option and RSU, other than fully vested awards, was modified and the exercise period of each stock option was extended. In determining the additional expense related to the modification of Mr. Ellis’ awards, the Company revalued the modified options in accordance with ASC 718 using the Black-Scholes model. In addition, the Company adopted ASU 2016-09, Improvements to Employee Share-Based Payment Accounting , for interim and annual reporting periods beginning January 1, 2017. As a result, the Company elected to account for forfeitures as they occur and no longer estimates the number of awards expected to be forfeited. The Company recognized total stock-based compensation cost in the amount of $6,920,220, $9,322,127 and $4,170,645 for the years ended December 31, 2015, 2016 and 2017, respectively. The Company’s stock option activity and related information are summarized as follows: Weighted-Average Remaining Weighted-Average Contractual Term Aggregate Options Exercise Price (In Years) Intrinsic Value Outstanding at January 1, 2015 5,096,674 $ 7.29 Granted during year 1,126,672 5.23 Exercised during year (146,046) 2.60 Expired during year (156,160) 11.03 Forfeited during year (234,325) 8.05 Outstanding at December 31, 2015 5,686,815 $ 6.87 6.52 $ 1,432,306 Exercisable at December 31, 2015 3,391,069 6.46 5.37 1,333,875 Outstanding at January 1, 2016 5,686,815 6.87 Granted during year 1,100,997 3.21 Exercised during year (129,638) 2.01 Expired during year (28,369) 7.65 Forfeited during year (182,211) 4.45 Outstanding at December 31, 2016 6,447,594 $ 6.41 6.17 $ 33,283 Exercisable at December 31, 2016 4,666,628 6.76 5.34 33,283 Outstanding at January 1, 2017 6,447,594 6.41 Granted during year 883,392 2.29 Exercised during year (378,030) 2.88 Expired during year (716,436) 8.02 Forfeited during year (357,860) 4.53 Outstanding at December 31, 2017 5,878,660 $ 5.93 5.83 $ 3,357,028 Exercisable at December 31, 2017 4,370,748 6.79 4.92 1,319,246 The following is a rollforward of the Company’s nonvested stock options from January 1, 2015 to December 31, 2017. Weighted-Average Options Grant Date Value Nonvested stock options at January 1, 2015 2,401,396 $ 7.07 Granted during year 1,126,672 4.34 Vested during year (997,997) 6.48 Forfeited during year (234,325) 6.37 Nonvested at December 31, 2015 2,295,746 $ 6.05 Nonvested stock options at January 1, 2016 2,295,746 $ 6.05 Granted during year 1,100,997 2.58 Vested during year (1,433,566) 5.74 Forfeited during year (182,211) 3.57 Nonvested at December 31, 2016 1,780,966 $ 4.41 Nonvested stock options at January 1, 2017 1,780,966 $ 4.41 Granted during year 883,392 1.81 Vested during year (798,586) 5.03 Forfeited during year (357,860) 3.63 Nonvested at December 31, 2017 1,507,912 $ 2.75 The total grant date value of stock options vested during 2015, 2016 and 2017 was $6,467,294, $8,233,220 and $4,015,344 respectively. As of December 31, 2016 and December 31, 2017, the total remaining unrecognized compensation cost related to stock options granted was $4.2 million and $2.1 million respectively, which is expected to be recognized over a weighted average period of approximately 1.4 and 1.6 years, respectively. The intrinsic value of options exercised was $126,651 and $635,925 for the years ended December 31, 2016 and December 31, 2017, respectively. Restricted Stock Units In May 2011, the Company adopted and granted awards under a performance-based RSU program (the “2011 PRSU Program”) under the 2010 Plan. All PRSU awards expired in the second quarter of 2016 when the performance deadline of May 26, 2016 passed. RSUs are service-based awards that will vest and be paid in the form of one share of the Company’s common stock for each RSU, generally in two, three or four equal annual installments beginning on the first anniversary of the date of grant of an RSU. As of December 31, 2017, the Company had 1,383,770 RSU awards outstanding. As of December 31, 2016 and 2017, the total remaining unrecognized compensation cost related to RSUs was $1.1 million and $5.7 million, respectively, each of which is expected to be recognized over a weighted average period of approximately 1.4 years. The following table sets forth the number of RSUs that were granted, vested and forfeited in the periods indicated: Weighted-Average Restricted Grant Date Stock Units Fair Value Outstanding at January 1, 2015 161,439 $ 11.11 Granted during year 260,976 5.17 Vested during year (40,333) 11.11 Forfeited during year (30,668) 8.07 Outstanding at December 31, 2015 351,414 $ 7.03 Outstanding at January 1, 2016 351,414 7.03 Granted during year 254,538 3.21 Vested during year (177,078) 6.71 Forfeited during year (34,742) 4.13 Outstanding at December 31, 2016 394,132 4.96 Outstanding at January 1, 2017 394,132 $ 4.96 Granted during year 1,300,068 4.90 Vested during year (158,112) 5.35 Forfeited during year (152,318) 3.15 Outstanding at December 31, 2017 1,383,770 $ 5.05 Employee Stock Purchase Plan Effective January 1, 2014, the Company implemented the ESPP. At January 1, 2017, 825,154 common shares were available for issuance under the ESPP. Shares may be issued under the ESPP twice a year. In the year ended December 31, 2017, plan participants purchased 55,612 shares of common stock under the ESPP at an average purchase price of $1.30 per share. At December 31, 2017, 769,542 shares were available for issuance under the ESPP.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Income Taxes	11. Income Taxes A reconciliation of the expected income tax benefit (expense) computed using the federal statutory income tax rate to the Company’s effective income tax rate is as follows for the years ended December 31, 2015, 2016, and 2017: December 31, 2015 2016 2017 Income tax computed at federal statutory tax rate 34.0 % 34.0 % 34.0 % State taxes, net of federal benefit 3.2 % 3.3 % 3.6 % International operations (4.8) % (0.7) % — Research and development credits 3.8 % 4.0 % 2.9 % Orphan drug credits 0.9 % 0.6 % 0.3 % Equity compensation (2.0) % (3.7) % (1.1) % Tax reform — — (60.3) % Change in valuation allowance (35.1) % (37.5) % 20.6 % Total — — — At December 31, 2017, the Company had net operating loss carryforwards totaling approximately $247,493,000 and $315,755,000 for federal and state income taxes, respectively, that may be used to offset future taxable income. If not used, the net operating loss carryforwards and research and development credits will begin expiring in the year 2021. The Company has determined that it experienced a change in ownership as defined under Section 382 of the U.S. Internal Revenue Code (the “Code”), as a result of the public offering in August 2011. As a result, the future use of its net operating losses, after giving effect to net unrealized built-in gains, will be limited to approximately $218,700,000 for 2017. Any available but unused amounts will become available for use in all successive years, subject to certain limitations. Utilization of these net operating loss carryforwards would require the Company to generate future taxable income prior to their expiration. Furthermore, the utilization of the net operating loss carryforwards could be limited beyond the Company's generation of taxable income if a change in the underlying ownership of the Company's common stock has occurred, resulting in a limitation on the amounts that could be utilized in any given period under Section 382 of the Code. Net deferred tax assets and liabilities are comprised of the following: December 31, 2016 2017 Deferred tax assets Net operating loss carryforwards $ 78,021,000 $ 62,921,000 Research and development credit carryforwards 14,143,000 16,456,000 Orphan drug credit 7,235,000 7,518,000 Stock options 7,105,000 4,766,000 Intangibles — 4,045,000 Other 562,000 334,000 Deferred tax assets 107,066,000 96,040,000 Deferred tax liabilities Property and equipment (337,000) (166,000) Deferred tax liabilities $ (337,000) $ (166,000) Net deferred tax asset before valuation allowance $ 106,729,000 $ 95,874,000 Less valuation allowance (106,729,000) (95,874,000) Net deferred tax assets $ — $ — For the year ended December 31, 2017, net operating loss carryforwards in the table above have been reduced by $2.3 million of uncertain tax liabilities. All deferred tax asset and liability balances have been revalued due to the 2017 Tax Act (as defined and discussed further below). A reconciliation of the beginning and ending amount of the unrecognized tax positions is as follows: Unrecognized Tax Positions Balance at January 1, 2016 $ — Additions based on tax positions related to the current year 3,405,000 Additions for tax positions of prior years — Reductions for tax positions of prior years — Settlements — Balance at January 1, 2017 3,405,000 Additions based on tax positions related to the current year — Additions for tax positions of prior years — Reductions for tax positions of prior years — Impact of 2017 Tax Act (1,131,000) Settlements — Balance at December 31, 2017 $ 2,274,000 At December 31, 2017 there were no uncertain tax liabilities that if recognized would affect the annual effective tax rate, due to the Company’s full valuation allowance. The Company does not recognize interest accrued related to unrecognized tax liabilities. On December 22, 2017, the President of the United States signed into law the Tax Cuts and Jobs Act (the “2017 Tax Act”) which, among other provisions, reduces the corporate income tax rate from 35% to 21% effective January 1, 2018. During the fourth quarter of 2017, the Company revalued its net deferred tax assets using the newly enacted rate, resulting in a reduction of its net deferred tax assets of $33.1 million. The Company also reduced its valuation allowance by $33.1 million, resulting in no income tax expense being recognized as a result of the revaluation. The Company’s estimate of the impact of the 2017 Tax Act is based upon its analysis and interpretations of currently available information. Uncertainties remain regarding the impact of the 2017 Tax Act due to future regulatory and rulemaking processes, prospects of additional corrective or supplemental legislation, and potential trade or other litigation. These uncertainties, along with the Company’s completion of the calculations and potential changes in its initial assumptions as new information becomes available, could cause the actual charge to ultimately differ from the provisional amount recorded in 2017 related to the enactment of the 2017 Tax Act.

Collaborations and Other Arrang

Collaborations and Other Arrangements	12 Months Ended
	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaborations	12. Collaboration and Other Arrangements ABX Development and License Agreement In September 2017, the Company entered into the License Agreement with ABX that grants the Company exclusive worldwide rights to develop and commercialize PSMA-617 agents. Under the terms of the License Agreement, the Company will be responsible for, and bear the future costs of, worldwide development and commercialization of PSMA-617. As consideration for the exclusive license, the Company made an upfront cash payment on September 29, 2017 of approximately $11.9 million to ABX, consisting of $12.0 million less an immaterial expense reimbursement amount, and issued to ABX 2,000,000 shares of the Company’s common stock (see Note 10 – Stockholders’ Equity of the Notes to Consolidated Financial Statements for additional information regarding this issuance) and two warrants to purchase, in the aggregate, 4,000,000 shares of the Company’s common stock (see Note 8 – Warrants of the Notes to Consolidated Financial Statements for additional information regarding the warrants). The License Agreement also obligates the Company to pay ABX regulatory milestone payments of up to $25.0 million, sales milestone payments of up to $135.0 million, and tiered royalties, beginning in the mid-teens and not to exceed the mid-twenties, based on percentages of net sales. The Company has accounted for the License Agreement as an asset acquisition and as a result, the upfront payment was expensed in the year ended December 31, 2017 as acquired IPR&D expense as the acquired asset did not have alternative future use. Any future regulatory milestone payments when paid or payable will be expensed as acquired IPR&D, provided that the drug has not achieved regulatory approval for marketing and, absent obtaining such approval, has no alternative future use. If the Company obtains regulatory approval for marketing for 177 Lu-PSMA-617 or any other PSMA-617 agents, any related milestone payments may be capitalized as an intangible asset and amortized over the life of the asset. The Company recorded $16.5 million of acquired IPR&D expenses related to the License Agreement in the year ended December 31, 2017 consisting of the following: · $12.0 million related to the upfront payment to ABX; · $3.8 million related to the fair value of common stock and warrant shares issued; and · $0.7 million of acquisition costs consisting primarily of legal and professional fees. The Company intends to initiate, in the second quarter of 2018, the VISION trial, an international, prospective, open-label, multicenter, randomized phase 3 study of 177 Lu-PSMA-617 and will enroll 750 patients with progressive PSMA-positive mCRPC. In October 2017, the Company entered into an agreement with RadioMedix, Inc., a biotechnology company focused on innovative targeted radiopharmaceuticals for diagnosis, monitoring and therapy of cancer, which enabled the transfer of a U.S. Investigational New Drug application of 177 Lu-PSMA-617 from the prior sponsor, RadioMedix, to the Company. This transfer helped accelerate the Company’s successful End of Phase 2 trial meeting with the FDA in early 2018 to confirm the phase 3 trial design and registration plan for 177 Lu-PSMA-617. In addition, under a three-party agreement, entered into in October 2017, among the Company, the University of Sydney (the “University”) and ANZUP, a cooperative cancer trials group operating in Australia and New Zealand pursuing research in genito-urinary malignancies, ANZUP sponsors jointly with the University a randomized phase 2 multi-center TheraP trial of 177 Lu-PSMA-617 versus cabazitaxel in 200 mCRPC patients. The TheraP trial commenced enrollment in the first quarter of 2018. Under the three-party agreement, the Company provides the PSMA-617 precursor molecule and financial support for the trial. The Company will have access to data generated from the trial, which is a potentially important supportive trial for future regulatory submissions. The primary financial obligations of the trial, along with labeling PSMA-617 with Lutetium-177, will be the responsibility of the University and ANZUP. NMP License and Commercialization Agreement In August 2013, the Company entered into a license and commercialization agreement with Nihon Medi-Physic Co., LTD. (“NMP”) that grants NMP the right to develop and commercialize etarfolatide in Japan for use in connection with any folate receptor-targeted small molecule drug conjugate (“SMDC”) in Japan. The Company received a $1.0 million non-refundable upfront payment, is eligible for up to $4.5 million based on the successful achievement of regulatory goals for etarfolatide in five different cancer indications and is eligible to receive double-digit percentage royalties on sales of etarfolatide in Japan. For revenue recognition purposes, the Company viewed the agreement with NMP as a multiple element arrangement. Multiple element arrangements are analyzed to determine whether the various performance obligations, or elements, can be separated or whether they must be accounted for as a single unit of accounting. The Company has identified the deliverables related to the collaboration with NMP, which include the license granted to NMP, as well as the obligation to provide pre-clinical and clinical supply of etarfolatide, to provide rights to NMP if a product is developed that replaces etarfolatide, the obligation for the Company to provide clinical data to NMP during the contract period and the coordination of development and commercialization efforts between the Company or any of its potential sub-licensees for any folate receptor-targeted SMDC and NMP for etarfolatide in Japan. The Company’s deliverables will be accounted for as a single unit of account, therefore the non-refundable upfront payment is being recognized on a straight-line basis over the performance period. This determination was made because the successful development of etarfolatide in Japan requires the ongoing participation by the Company, including the development of the related folate receptor-targeted SMDC therapeutic drug. The performance period over which the revenue will be recognized continues from the date of execution of the agreement through the end of 2033, the estimated termination date of the contract which is when the Company’s performance obligations will be completed. Any significant changes in the timing of the performance period could result in a change in the revenue recognition period. The Company had deferred revenue related to the agreement of approximately $0.8 million at December 31, 2017. Subsequent to the inception of the NMP arrangement, the Company evaluates the remaining deliverables for separation as items in the arrangement are delivered. The arrangement with NMP includes milestone payments of up to approximately $4.5 million and the milestones are based on the commencement of clinical trials in Japan for specific and non-specific indications and filing for approval in Japan for specific and non-specific indications. The Company evaluated each of these milestone payments and believes that all of the milestones are substantive as there is substantial performance risk that must occur in order for them to be met because the Company must complete additional clinical trials which show a positive outcome or receive approval from a regulatory authority and would be commensurate with the enhancement of value of the underlying intellectual property. To date, the products have not been approved in Japan and no revenue has been recognized related to the regulatory milestones or royalties as continued development of any folate receptor-targeted SMDC is still an opportunity that the Company could pursue in the future. NMP has the right to terminate the collaboration agreement on 90 days notice prior to the first commercial sale in Japan and six months notice after the first commercial sale in Japan. NMP also has the right to terminate the agreement on six months notice if the Company fails to launch any folate receptor-targeted SMDC therapeutic drug after receiving regulatory approval in Japan. NMP and the Company each have the right to terminate the agreement due to the material breach or insolvency of the other party. Upon termination of the agreement depending on the circumstances, the parties have varying rights and obligations with respect to licensing and related regulatory materials and data. Other Agreements In October 2007, the Company entered into an exclusive worldwide license with R&D Biopharmaceuticals to research, develop, and commercialize products containing conjugates of folate receptor targeting compounds and tubulysin compounds. In February 2011, this licensing agreement was assigned by R&D Biopharmaceuticals to Trientlgasse. The Company paid an upfront fee of $300,000 as research and development and pays $25,000 in annual maintenance fees unless a milestone is paid in a given year. The Company could pay $5,900,000 in additional contingent payments upon the achievement of specific scientific, clinical, and regulatory milestones, in addition to royalties upon commercial sales. All payments have been expensed as research and development as incurred, as there is no alternate future use for this technology. In December 1995, as amended in October 1998, the Company entered into an exclusive license agreement with Purdue Research Foundation, which licenses the right under certain patents to the Company. The Company is obligated to pay an annual minimum royalty of $12,500 until commercial sales commence, following which time the payment of low single digit royalty rates will commence. All payments have been expensed as incurred. The Company does not anticipate incurring any liabilities for vintafolide royalty payments. In December 2009, the Company entered into a financial term sheet to be incorporated into a written license agreement with Purdue Research Foundation for a patent related to prostate cancer. The agreement was signed and became effective on March 1, 2010. Pursuant to the exclusive license agreement, the Company is subject to minimum annual royalty payments of $15,000, payable until first commercial sale, following which time the minimum annual royalty payments increase to $100,000 and low single digit sales-based royalty rates are also payable when commercial sales commence. In addition, a milestone payment of $500,000 is payable upon approval of a new drug application in the U.S. In 2014, the Company paid a penalty as a milestone was not met. In 2015, the Company accrued a penalty which was paid in the first quarter of 2016 as an additional milestone was not met. There were no additional penalties or milestone payments accrued or paid in the years ended December 31, 2016 or 2017. In 2014, the Company entered into a Master License Agreement with Purdue Research Foundation. Under this license, the Company has the right to exclusively license patents and technology discovered under company funded research at Purdue University. If the Company decides to move forward with development of one or more of these technologies, the Company will be obligated to make an acceptance payment and the Company will also be obligated to make contingent payments upon the achievement of specific scientific, clinical and regulatory milestones. Certain scientific, clinical and regulatory milestones, in addition to internal resource targets must be met by the Company to avoid fees as consideration for waivers of potentially missed milestones. The Company is obligated to pay annual minimum payments until commercial sales commence, following which time the payment of low single digit royalty rates will commence, along with an annual royalty payment.

Related-Party Transactions

Related-Party Transactions	12 Months Ended
	Dec. 31, 2017
Related Party Transactions [Abstract]
Related Party Transactions Disclosure [Text Block]	13. Related-Party Transactions The Company funds research at Purdue University, the employer of one of its founders and current Chief Science Officer. Amounts included in research and development expenses were $1,000,000, $1,069,000, and $781,000 for the years ended December 31, 2015, 2016 and 2017, respectively. The Company leases a facility from Purdue Research Foundation, a nonprofit organization affiliated with Purdue University, the employer of the Company’s Chief Science Officer. The prior lease agreements have generally been renewed annually, and the current lease agreement expires June 30, 2018 with an option to extend the term. The amounts paid to Purdue Research Foundation related to the lease of this facility were $588,000, $597,000 and $609,000 for the years ended December 31, 2015, 2016 and 2017, respectively. At December 31, 2017, the Company had a balance of $29,600 in accounts payable and other liabilities due to Purdue University and Purdue Research Foundation related to the license agreements, the lease agreement and other operating expenses. In September 2011, the Company entered into exclusive worldwide licenses with On Target Laboratories, L.L.C. (“On Target”) to develop and commercialize products relating to the compound comprising the Company’s Folate and DUPA ligands and other certain licensed patents. On Target’s Chief Executive Officer is the brother of the Company’s Chief Science Officer. On Target is solely responsible for conducting research and development, seeking regulatory approval and commercialization of products. The Company received nonrefundable upfront license fees totaling $191,000 from On Target in December 2011. The Company has determined that the deliverables under this agreement do not meet the criteria required for separate accounting units for the purposes of revenue recognition, and as a result, the Company recognized revenue from non-refundable, upfront fees when the performance condition of delivering the licenses and certain consultation services had been achieved and there was reasonable assurance of collectability. If On Target fails to meet minimum spend requirements on research and development, the Company has the right to terminate the agreement. The Company will be entitled to receive minimum royalty payments annually based on net sales, but there is no guarantee that a commercial product will be developed and approved for commercial sales. The Company will also be entitled to reimbursement of expenses relating to patent expenses and payments to the inventors and Purdue University if certain milestones are met. During 2011, the Company received a $50,000 reimbursement from On Target for payments made to inventors for issued patents. The Company received $20,000 in annual maintenance license fees during each of 2015, 2016 and 2017, and received $21,044, $14,397 and $6,349 for reimbursable research and development expenses for 2015, 2016 and 2017, respectively.

Retirement Plans

Retirement Plans	12 Months Ended
	Dec. 31, 2017
Compensation and Retirement Disclosure [Abstract]
Pension and Other Postretirement Benefits Disclosure [Text Block]	14. Retirement Plans The Company maintains a 401(k) retirement savings plan to provide retirement benefits for substantially all of its employees. Participants in the plan may elect to contribute a portion of their annual compensation to the plan, limited to the maximum allowed by the Code. Prior to January 1, 2014 the Company did not match 401(k) contributions. Effective January 1, 2014, the Company implemented a matching contribution for the 401(k) contributions. For each of the years ended December 31, 2015, 2016, and 2017, the Company had approximately $0.3 million of expense related to the 401(k) employer match.

Restructuring Costs

Restructuring Costs	12 Months Ended
	Dec. 31, 2017
Restructuring Costs [Abstract]
Restructuring and Related Activities Disclosure [Text Block]	15. Restructuring Costs In June 2017, the Company refocused its clinical development efforts and aligned its resources to focus on the Company’s highest value opportunities while maintaining key capabilities. The Company’s restructuring activities included a reduction of its workforce by approximately 40%, as well as stopping enrollment in its EC1456 phase 1b trial as the assessment of trial data did not yield the level of clinical activity necessary to support continued advancement of EC1456. In December 2017, the Company stopped enrollment in its EC1456 ovarian cancer surgical trial. Pursuant to ASC Topic 420, Exit or Disposal Cost Obligations , the Company recorded $2.3 million of restructuring expenses in the year ended December 31, 2017 as follows: · included in research and development expenses were expenses for employee termination benefits of $0.9 million, $0.9 million for the remaining EC1456 phase 1b trial expenses, including site close-out expenses, $0.3 million related to other restructuring expenses, and $0.1 million related to fixed asset impairment charges; and · included in general and administrative expenses were expenses for employee termination benefits of $0.1 million. As of December 31, 2017, the Company had paid all severance and other costs related to the restructuring activities, and had a clinical trial accrual balance related to the EC1456 phase 1b trial termination of $0.1 million, which is expected to be fully paid by the end of the first quarter of 2018. The following table summarizes the restructuring accrual related to the June 2017 restructuring activities for the year ended December 31, 2017. EC1456 Employee Phase 1b Trial Other Termination Termination Restructuring Accrual Accrual Costs Accrual Total Balance, January 1, 2017 $ — $ — $ — $ — Charges for the year ended December 31, 2017 1,029,400 947,100 126,500 2,103,000 Revised estimates in the year ended December 31, 2017 — (30,000) — (30,000) Amounts paid in the year ended December 31, 2017 (1,029,400) (810,200) (126,500) (1,966,100) Balance, December 31, 2017 $ — $ 106,900 $ — $ 106,900 The Company terminated the PROCEED trial in May 2014 after the interim futility analysis indicated that vintafolide did not demonstrate efficacy on the pre-specified outcome of progression-free survival for the treatment of platinum-resistant ovarian cancer. As a result, the Company ceased its pre-launch commercial activities in Europe and implemented staff reductions in Europe and in the U.S. At December 31, 2016 and 2017, the Company had no remaining accrual balance related to the PROCEED trial termination. The following table summarizes the restructuring accruals related to the PROCEED trial termination for the years ended December 31, 2015 and 2016: PROCEED Trial Termination Accrual Balance, January 1, 2015 $ 1,300,000 Revised estimates in the year ended December 31, 2015 134,000 Amounts paid in the year ended December 31, 2015 (1,387,400) Balance, December 31, 2015 $ 46,600 Balance, January 1, 2016 $ 46,600 Revised estimates in the year ended December 31, 2016 (15,800) Amounts paid in the year ended December 31, 2016 (30,800) Balance, December 31, 2016 $ —

Selected Quarterly Financial Da

Selected Quarterly Financial Data (unaudited)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Text Block]	16. Selected Quarterly Financial Data (unaudited) The following tables summarize the unaudited statements of operations for each quarter of 2017 and 2016 (in thousands except share and per share amounts): Quarters Ended March 31, June 30, September 30, December 31, 2017 Revenue $ 12 $ 13 $ 33 $ 12 Operating expenses: Research and development 7,994 8,655 4,090 5,128 General and administrative 3,745 3,306 3,011 3,708 Acquired in-process research and development — — 16,493 46 Loss from operations (11,727) (11,948) (23,561) (8,870) Interest income, net 235 234 265 295 Other income (expense), net 3 (30) 29 11 Net loss $ (11,489) $ (11,744) $ (23,267) $ (8,564) Net loss per share-basic and diluted (1) (2) $ (0.27) $ (0.28) $ (0.55) $ (0.18) Weighted average common shares outstanding – basic and diluted (2) 42,434,709 42,503,584 42,636,567 47,979,127 Quarters Ended March 31, June 30, September 30, December 31, 2016 Revenue $ 12 $ 13 $ 33 $ 12 Operating expenses: Research and development 6,531 6,788 5,985 8,188 General and administrative 3,820 7,394 2,988 3,096 Loss from operations (10,339) (14,169) (8,940) (11,272) Interest income, net 189 208 232 232 Other expense, net (3) (1) — (25) Net loss $ (10,153) $ (13,962) $ (8,708) $ (11,065) Net loss per share-basic and diluted (1) (2) $ (0.24) $ (0.33) $ (0.21) $ (0.26) Weighted average common shares outstanding – basic and diluted (2) 42,109,828 42,178,537 42,263,311 42,289,453 (1) Per common share amounts for the quarters and full years have been calculated separately. Accordingly, the sum of quarterly amounts may not equal the annual amount due to differences in the weighted average common shares outstanding during each period, principally due to the effect of share issuances by the Company during the year. (2) Diluted weighted average common shares outstanding are identical to basic weighted average common shares outstanding and diluted net loss per share is identical to basic net loss per share for all quarters of 2016 and 2017 because common share equivalents are excluded from the calculations of diluted weighted average common shares outstanding for those quarters, as their effect is anti-dilutive.

Significant Accounting Polici23

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include the accounts of Endocyte, Inc. and its subsidiaries and all intercompany amounts have been eliminated as of December 31, 2015. The accompanying financial statements for the years ended December 31, 2016 and 2017 include only the accounts of Endocyte, Inc. as the Company dissolved Endocyte Europe GmbH and Endocyte Europe B.V. in the fourth quarter of 2015 and the first quarter of 2016, respectively. There were no intercompany transactions in the years ended December 31, 2016 or 2017 and no intercompany balances as of December 31, 2016 or 2017. The consolidated financial statements are prepared in conformity with U.S. generally accepted accounting principles (“GAAP”) for annual financial information to Form 10-K. Subsequent events have been evaluated through the date of issuance, which is the same as the date this Form 10-K is filed with the Securities and Exchange Commission (the “SEC”).
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires the Company’s management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. Actual amounts may differ from those estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers cash and all highly liquid investments with an original maturity of three months or less at the date of purchase to be cash equivalents. Cash equivalents consist primarily of money market instruments, U.S. government treasury obligations, corporate debt securities and repurchase agreements that are maintained by an investment manager.
Investments	Investments Investments consist primarily of investments in U.S. Treasuries and corporate debt securities, which could also include commercial paper, that are maintained by an investment manager. Management determines the appropriate classification of marketable securities at the time of purchase and reevaluates such classification as of each balance sheet date. Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in other comprehensive income. Realized gains and losses and declines in value judged to be other-than-temporary on available-for-sale securities are included in other income. The Company considers and accounts for other-than-temporary impairments according to the Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 320, Investments — Debt and Equity Securities (“ASC 320”). The cost of securities sold is based on the specific-identification method. Discounts and premiums on debt securities are amortized to interest income and expensed over the term of the security.
Property and Equipment	Property and Equipment Property and equipment are stated at cost and are being depreciated using the straight-line method over estimated useful lives, which range from three to seven years.
Licenses and Patents	Licenses and Patents Licenses and patent costs are expensed as incurred as the Company does not believe there is an alternate future use for the costs. Licenses are classified as research and development expenses and patents are classified as general and administrative expenses in the consolidated statements of operations.
Long-Lived Assets	Long-Lived Assets The Company reviews long-lived assets, including property and equipment, for impairment when events or changes in business conditions indicate that their full carrying value may not be fully recoverable.
Leases	Leases The Company evaluates all leases to determine whether they should be accounted for as operating or capital leases.
Revenue Recognition	Revenue Recognition The Company recognizes revenues from license and collaboration agreements when persuasive evidence of an arrangement exists, delivery has occurred or services have been rendered, the fee is fixed or determinable, and there is reasonable assurance that the related amounts are collectible in accordance with ASC Topic 605, Revenue Recognition (“ASC 605”). The Company’s license and collaboration agreements may contain multiple elements, including grants of licenses to intellectual property rights, agreement to provide research and development services and other deliverables. The deliverables under such arrangements are evaluated under ASC Subtopic 605-25, Multiple-Element Arrangements (“ASC 605-25”). Under ASC 605-25, each required deliverable is evaluated to determine whether it qualifies as a separate unit of accounting based on whether the deliverable has “stand-alone value” to the customer. The arrangement’s consideration that is fixed or determinable, excluding contingent milestone payments and royalties, is then allocated to each separate unit of accounting based on the relative selling price of each deliverable. In general, the consideration allocated to each unit of accounting is recognized as the related goods or services are delivered, limited to the consideration that is not contingent upon future deliverables. Upfront payments for licensing the Company’s intellectual property are evaluated to determine if the licensee can obtain stand-alone value from the license separate from the value of the research and development services and other deliverables in the arrangement to be provided by the Company. If at the inception of an arrangement the Company determines that the license does not have stand-alone value separate from the research and development services or other deliverables, the license, services and other deliverables are combined as one unit of account and upfront payments are recorded as deferred revenue on the balance sheet and are recognized in a manner consistent with the final deliverable. Subsequent to the inception of an arrangement, the Company evaluates the remaining deliverables for separation as items in the arrangement are delivered. When stand-alone value is identified, the related consideration is recorded as revenue in the period in which the license or other intellectual property rights are delivered. In those circumstances where research and development services or other deliverables are combined with the license, and multiple services are being performed such that a common output measure to determine a pattern of performance cannot be discerned, the Company recognizes amounts received on a straight line basis over the performance period. Such amounts are recorded as collaboration revenue. Any subsequent reimbursement payments, which are contingent upon the Company’s future research and development expenditures, will be recorded as collaboration revenue and will be recognized on a straight-line basis over the performance period using the cumulative catch up method. The costs associated with these activities are reflected as a component of research and development expense in the statements of operations in the period incurred. In the event of an early termination of a collaboration agreement, any deferred revenue is recognized in the period in which all obligations of the Company under the agreement have been fulfilled. Milestone payments under collaborative arrangements are triggered either by the results of the Company’s research and development efforts, achievement of regulatory goals or by specified sales results by a third-party collaborator. Milestones related to the Company’s development-based activities may include initiation of various phases of clinical trials and applications and acceptance for product approvals by regulatory agencies. Due to the uncertainty involved in meeting these development-based milestones, the determination is made at the inception of the collaboration agreement whether the development-based milestones are considered to be substantive (i.e. not just achieved through passage of time). In addition, the amounts of the payments assigned thereto are considered to be commensurate with the enhancement of the value of the delivered intellectual property as a result of the Company’s performance. Because the Company’s involvement is necessary to the achievement of development-based milestones, the Company would account for development-based milestones as revenue upon achievement of the substantive milestone events. Milestones related to sales-based activities may be triggered upon events such as first commercial sale of a product or when sales first achieve a defined level. Since these sales-based milestones would be achieved after the completion of the Company’s development activities, the Company would account for the sales-based milestones in the same manner as royalties, with revenue recognized upon achievement of the milestone. Royalties based on reported sales of licensed products will be recognized based on contract terms when reported sales are reliably measurable and collectability is reasonably assured. To date, none of the Company’s products have been approved and therefore the Company has not earned any royalty revenue from product sales. In territories where the Company and a collaborator may share profit, the revenue would be recorded in the period earned. The Company often is required to make estimates regarding drug development and commercialization timelines for compounds being developed pursuant to a collaboration agreement. Because the drug development process is lengthy and the Company’s collaboration agreements typically cover activities over several years, this approach often results in the deferral of significant amounts of revenue into future periods. In addition, because of the many risks and uncertainties associated with the development of drug candidates, the Company’s estimates regarding the period of performance may change in the future. Any change in the Company’s estimates or a termination of the arrangement could result in substantial changes to the period over which the revenues are recognized.
Research and Development Expenses	Research and Development Expenses Research and development expenses represent costs associated with the ongoing development of novel therapeutics and companion imaging agents for personalized targeted therapies and include salaries and employee benefits, supplies, facility costs related to research activities, and expenses for clinical trials. The Company records accruals for clinical trial expenses based on the estimated amount of work completed. The Company monitors patient enrollment levels and related activities to the extent possible through internal reviews, correspondence, and discussions with research organizations. In the event that a clinical trial is terminated early, the Company records, in the period of termination, an accrual for the estimated remaining costs to complete and close out the trial pursuant to ASC Topic 420, Exit or Disposal Cost Obligations , as a terminated trial does not provide any future economic benefit to the Company. See Note 15 – Restructuring Costs of the Notes to Consolidated Financial Statements contained herein for costs incurred during the years ended December 31, 2015, 2016, and 2017 related to the Company’s restructuring activities. Upfront payments made in connection with business collaborations and research and development arrangements are evaluated under ASC Subtopic 730-20, Research and Development Arrangements . Amounts related to future research and development are capitalized as prepaid research and development and are expensed over the service period based upon the level of services provided. As of December 31, 2017, the Company had approximately $0.1 million of capitalized research and development costs included in prepaid expenses.
Acquired In-Process Research and Development Expense	Acquired In-Process Research and Development Expense The Company has acquired and may continue to acquire the rights to develop and commercialize new drug candidates. In accordance with ASC Subtopic 730-25, Accounting for Research and Development Costs, the upfront payments to acquire a new drug compound, as well as future milestone payments when paid or payable, are immediately expensed as acquired in-process research and development (“IPR&D”) in transactions other than a business combination provided that the drug has not achieved regulatory approval for marketing and, absent obtaining such approval, has no alternative future use. Upon obtaining regulatory approval for marketing, any related milestone payments may be capitalized and amortized over the life of the asset.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for its stock-based compensation pursuant to ASC Topic 718, Compensation — Stock Compensation (“ASC 718”), which requires the recognition of the fair value of stock-based compensation in net income. Stock-based compensation consists of stock options, which are granted at exercise prices at or above the fair market value of the Company’s common stock on the dates of grant, service-based restricted stock units (“RSUs”), performance-based RSUs (“PRSUs”), and shares available for purchase under the Company’s 2010 Employee Stock Purchase Plan (“ESPP”). For PRSUs issued by the Company, stock-based compensation expense would be recognized if and when the Company determines that it is probable that the performance conditions will be achieved. For RSUs and stock options issued by the Company, stock-based compensation expense is recognized ratably over the service period. The Company recognizes compensation cost based on the grant-date fair value estimated in accordance with the provisions of ASC 718.
Net Loss Per Share	Net Loss Per Share The Company calculates basic net loss per share based on the weighted-average number of outstanding common shares. The Company calculates diluted net loss per share based on the weighted-average number of outstanding common shares plus the effect of dilutive securities.
Income Taxes	Income Taxes The Company accounts for income taxes under the liability method in accordance with the provision of ASC Topic 740, Income Taxes (“ASC 740”). ASC 740 requires recognition of deferred taxes to provide for temporary differences between financial reporting and tax basis of assets and liabilities. Deferred taxes are measured using enacted tax rates expected to be in effect in a year in which the basis difference is expected to reverse. The Company continues to record a valuation allowance for the full amount of deferred tax assets, which would otherwise be recorded for tax benefits relating to operating loss and tax credit carryforwards, as realization of such deferred tax assets cannot be determined to be more likely than not. The Company accounts for uncertain income tax positions recognized in the financial statements in accordance with Accounting Standards Update (“ASU”) No. 2009-06. This guidance prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return and provides guidance on derecognition of tax benefits, classification on the balance sheet, interest and penalties, accounting in interim periods, disclosure, and transition.
Segment Information	Segment Information Operating segments are defined as components of an enterprise engaging in business activities for which discrete financial information is available and regularly reviewed by the chief operating decision maker in deciding how to allocate resources and in assessing performance. The Company had performed clinical trials globally and established a subsidiary in The Netherlands to assist in the administration of filing applications in Europe and a subsidiary in Switzerland for commercial pre-launch activities in Europe. The applications filed in Europe were withdrawn in May 2014 and the pre-launch activities in Europe ceased. The Company dissolved Endocyte Europe GmbH in the fourth quarter of 2015 and dissolved Endocyte Europe B.V. in the first quarter of 2016. All long-lived assets are held in the U.S. The Company views its operations and manages its business in one operating segment.

Net Loss per Share (Tables)

Net Loss per Share (Tables)	12 Months Ended
	Dec. 31, 2017
Earnings Per Share [Abstract]
Schedule of common stock equivalents excluded due to anti-dilutive effect	Year Ended December 31, 2015 2016 2017 Outstanding common stock options 5,686,815 6,447,594 5,878,660 Outstanding warrants 34,647 34,647 722,000 Outstanding PRSUs 213,758 — — Outstanding RSUs 351,414 394,132 1,383,770 Shares to be purchased under the ESPP 4,236 4,394 2,634 Total 6,290,870 6,880,767 7,987,064

Other Comprehensive Income (L25

Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2017
Other Comprehensive Income (Loss), Tax [Abstract]
Schedule of components of other comprehensive income	Foreign Accumulated Currency Unrealized Net Other Translation Gains (Losses) Comprehensive Gains (Losses) on Securities Gains (Losses) Balance at December 31, 2014 $ (50,592) $ (93,336) $ (143,928) Unrealized gain (loss) (1,352) 18,841 17,489 Net amount reclassified to net loss 51,944 (4,904) 47,040 Other comprehensive income 50,592 13,937 64,529 Balance at December 31, 2015 $ — $ (79,399) $ (79,399) Unrealized gain — 36,908 36,908 Net amount reclassified to net loss — 1,295 1,295 Other comprehensive income — 38,203 38,203 Balance at December 31, 2016 $ — $ (41,196) $ (41,196) Unrealized loss — (23,237) (23,237) Other comprehensive loss — (23,237) (23,237) Balance at December 31, 2017 $ — $ (64,433) $ (64,433)
Schedule of reclassifications out of AOCI	Reclassifications Out of Accumulated Other Comprehensive Income (Loss) Amount Reclassified from Accumulated Other Comprehensive Income (Loss) Affected Line Item in the Year Ended Year Ended Year Ended Consolidated Details about Accumulated Other December 31, December 31, December 31, Statements of Operations and Comprehensive Income (Loss) Components 2015 2016 2017 Comprehensive Income (Loss) Unrealized Net Gains (Losses) on Securities $ (4,904) $ 1,295 $ — Other income (expense) Foreign Currency Translation Losses 51,944 — — Other income (expense) Total Reclassifications for the Period $ 47,040 $ 1,295 $ —

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Schedule of the fair value of cash and cash equivalents and investments	The following table summarizes the fair value of cash and cash equivalents and investments as of December 31, 2016: Fair Value Description Cost Level 1 Level 2 (Carrying Value) Cash Cash $ 6,249,703 $ 6,249,703 $ — $ 6,249,703 Cash equivalents (original maturity of 3 months or less) FDIC insured deposits and money market funds 24,978,489 24,978,489 — 24,978,489 Cash and cash equivalents $ 31,228,192 $ 31,228,192 $ — $ 31,228,192 Short-term investments (due within 1 year) U.S. government treasury obligations $ 86,078,622 $ 86,053,755 $ — $ 86,053,755 Corporate obligations 20,941,799 — 20,925,469 20,925,469 Total short-term investments $ 107,020,420 $ 86,053,755 $ 20,925,469 $ 106,979,224 The following table summarizes the fair value of cash and cash equivalents and investments as of December 31, 2017: Fair Value Description Cost Level 1 Level 2 (Carrying Value) Cash Cash $ 2,544,972 $ 2,544,972 $ — $ 2,544,972 Cash equivalents (original maturity of 3 months or less) Repurchase agreements 10,000,000 — 10,000,000 10,000,000 Money market funds 6,014,158 6,014,158 — 6,014,158 Cash and cash equivalents $ 18,559,130 $ 8,559,130 $ 10,000,000 $ 18,559,130 Short-term investments (due within 1 year) U.S. government treasury obligations $ 63,034,548 $ 62,970,115 $ — $ 62,970,115 Corporate obligations 15,942,182 — 15,942,182 15,942,182 Total short-term investments $ 78,976,730 $ 62,970,115 $ 15,942,182 $ 78,912,297

Property and Equipment (Tables)

Property and Equipment (Tables)	12 Months Ended
	Dec. 31, 2017
Property, Plant and Equipment [Abstract]
Property and equipment	Estimated December 31, Useful Lives 2016 2017 Laboratory equipment 7 $ 6,666,506 $ 5,626,280 Office equipment and software 3 – 7 1,347,768 1,245,232 Leasehold improvements 7 424,176 424,176 Assets not in service 19,000 66,809 8,457,450 7,362,497 Less accumulated depreciation (5,252,373) (5,180,098) $ 3,205,077 $ 2,182,399

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2017
Leases [Abstract]
Schedule of future minimum lease payment for noncancellable operating leases	Future minimum lease payments for noncancellable operating leases as of December 31, 2017, are as follows: 2018 $ 304,523 2019 — 2020 — 2021 — 2022 — Thereafter — Total minimum lease payments $ 304,523

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2017
Equity [Abstract]
Schedule of weighted-average valuation assumptions	Year Ended December 31, 2015 2016 2017 Expected volatility 106.38 % 98.83 % 92.98 % Risk-free interest rate 1.55 % 1.47 % 2.15 % Weighted-average expected life (in years) 6.4 6.6 6.9 Dividend yield % % 0.00 %
Schedule of stock option activity	The Company’s stock option activity and related information are summarized as follows: Weighted-Average Remaining Weighted-Average Contractual Term Aggregate Options Exercise Price (In Years) Intrinsic Value Outstanding at January 1, 2015 5,096,674 $ 7.29 Granted during year 1,126,672 5.23 Exercised during year (146,046) 2.60 Expired during year (156,160) 11.03 Forfeited during year (234,325) 8.05 Outstanding at December 31, 2015 5,686,815 $ 6.87 6.52 $ 1,432,306 Exercisable at December 31, 2015 3,391,069 6.46 5.37 1,333,875 Outstanding at January 1, 2016 5,686,815 6.87 Granted during year 1,100,997 3.21 Exercised during year (129,638) 2.01 Expired during year (28,369) 7.65 Forfeited during year (182,211) 4.45 Outstanding at December 31, 2016 6,447,594 $ 6.41 6.17 $ 33,283 Exercisable at December 31, 2016 4,666,628 6.76 5.34 33,283 Outstanding at January 1, 2017 6,447,594 6.41 Granted during year 883,392 2.29 Exercised during year (378,030) 2.88 Expired during year (716,436) 8.02 Forfeited during year (357,860) 4.53 Outstanding at December 31, 2017 5,878,660 $ 5.93 5.83 $ 3,357,028 Exercisable at December 31, 2017 4,370,748 6.79 4.92 1,319,246
Schedule of restricted stock unit activity	Weighted-Average Restricted Grant Date Stock Units Fair Value Outstanding at January 1, 2015 161,439 $ 11.11 Granted during year 260,976 5.17 Vested during year (40,333) 11.11 Forfeited during year (30,668) 8.07 Outstanding at December 31, 2015 351,414 $ 7.03 Outstanding at January 1, 2016 351,414 7.03 Granted during year 254,538 3.21 Vested during year (177,078) 6.71 Forfeited during year (34,742) 4.13 Outstanding at December 31, 2016 394,132 4.96 Outstanding at January 1, 2017 394,132 $ 4.96 Granted during year 1,300,068 4.90 Vested during year (158,112) 5.35 Forfeited during year (152,318) 3.15 Outstanding at December 31, 2017 1,383,770 $ 5.05
Schedule of nonvested stock option activity	Weighted-Average Options Grant Date Value Nonvested stock options at January 1, 2015 2,401,396 $ 7.07 Granted during year 1,126,672 4.34 Vested during year (997,997) 6.48 Forfeited during year (234,325) 6.37 Nonvested at December 31, 2015 2,295,746 $ 6.05 Nonvested stock options at January 1, 2016 2,295,746 $ 6.05 Granted during year 1,100,997 2.58 Vested during year (1,433,566) 5.74 Forfeited during year (182,211) 3.57 Nonvested at December 31, 2016 1,780,966 $ 4.41 Nonvested stock options at January 1, 2017 1,780,966 $ 4.41 Granted during year 883,392 1.81 Vested during year (798,586) 5.03 Forfeited during year (357,860) 3.63 Nonvested at December 31, 2017 1,507,912 $ 2.75

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Schedule of effective income tax rate reconciliation	December 31, 2015 2016 2017 Income tax computed at federal statutory tax rate 34.0 % 34.0 % 34.0 % State taxes, net of federal benefit 3.2 % 3.3 % 3.6 % International operations (4.8) % (0.7) % — Research and development credits 3.8 % 4.0 % 2.9 % Orphan drug credits 0.9 % 0.6 % 0.3 % Equity compensation (2.0) % (3.7) % (1.1) % Tax reform — — (60.3) % Change in valuation allowance (35.1) % (37.5) % 20.6 % Total — — —
Schedule of deferred tax assets and liabilities	December 31, 2016 2017 Deferred tax assets Net operating loss carryforwards $ 78,021,000 $ 62,921,000 Research and development credit carryforwards 14,143,000 16,456,000 Orphan drug credit 7,235,000 7,518,000 Stock options 7,105,000 4,766,000 Intangibles — 4,045,000 Other 562,000 334,000 Deferred tax assets 107,066,000 96,040,000 Deferred tax liabilities Property and equipment (337,000) (166,000) Deferred tax liabilities $ (337,000) $ (166,000) Net deferred tax asset before valuation allowance $ 106,729,000 $ 95,874,000 Less valuation allowance (106,729,000) (95,874,000) Net deferred tax assets $ — $ —
Schedule of unrecognized tax benefits	Unrecognized Tax Positions Balance at January 1, 2016 $ — Additions based on tax positions related to the current year 3,405,000 Additions for tax positions of prior years — Reductions for tax positions of prior years — Settlements — Balance at January 1, 2017 3,405,000 Additions based on tax positions related to the current year — Additions for tax positions of prior years — Reductions for tax positions of prior years — Impact of 2017 Tax Act (1,131,000) Settlements — Balance at December 31, 2017 $ 2,274,000

Restructuring Costs (Tables)

Restructuring Costs (Tables)	12 Months Ended
	Dec. 31, 2017
Restructuring Costs [Abstract]
Schedule of restructuring and related costs	The following table summarizes the restructuring accruals related to the PROCEED trial termination for the years ended December 31, 2015 and 2016: PROCEED Trial Termination Accrual Balance, January 1, 2015 $ 1,300,000 Revised estimates in the year ended December 31, 2015 134,000 Amounts paid in the year ended December 31, 2015 (1,387,400) Balance, December 31, 2015 $ 46,600 Balance, January 1, 2016 $ 46,600 Revised estimates in the year ended December 31, 2016 (15,800) Amounts paid in the year ended December 31, 2016 (30,800) Balance, December 31, 2016 $ —

Selected Quarterly Financial 32

Selected Quarterly Financial Data (unaudited) (Tables)	12 Months Ended
	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Schedule of quarterly financial information	The following tables summarize the unaudited statements of operations for each quarter of 2017 and 2016 (in thousands except share and per share amounts): Quarters Ended March 31, June 30, September 30, December 31, 2017 Revenue $ 12 $ 13 $ 33 $ 12 Operating expenses: Research and development 7,994 8,655 4,090 5,128 General and administrative 3,745 3,306 3,011 3,708 Acquired in-process research and development — — 16,493 46 Loss from operations (11,727) (11,948) (23,561) (8,870) Interest income, net 235 234 265 295 Other income (expense), net 3 (30) 29 11 Net loss $ (11,489) $ (11,744) $ (23,267) $ (8,564) Net loss per share-basic and diluted (1) (2) $ (0.27) $ (0.28) $ (0.55) $ (0.18) Weighted average common shares outstanding – basic and diluted (2) 42,434,709 42,503,584 42,636,567 47,979,127 Quarters Ended March 31, June 30, September 30, December 31, 2016 Revenue $ 12 $ 13 $ 33 $ 12 Operating expenses: Research and development 6,531 6,788 5,985 8,188 General and administrative 3,820 7,394 2,988 3,096 Loss from operations (10,339) (14,169) (8,940) (11,272) Interest income, net 189 208 232 232 Other expense, net (3) (1) — (25) Net loss $ (10,153) $ (13,962) $ (8,708) $ (11,065) Net loss per share-basic and diluted (1) (2) $ (0.24) $ (0.33) $ (0.21) $ (0.26) Weighted average common shares outstanding – basic and diluted (2) 42,109,828 42,178,537 42,263,311 42,289,453 (1) Per common share amounts for the quarters and full years have been calculated separately. Accordingly, the sum of quarterly amounts may not equal the annual amount due to differences in the weighted average common shares outstanding during each period, principally due to the effect of share issuances by the Company during the year. Diluted weighted average common shares outstanding are identical to basic weighted average common shares outstanding and diluted net loss per share is identical to basic net loss per share for all quarters of 2016 and 2017 because common share equivalents are excluded from the calculations of diluted weighted average common shares outstanding for those quarters, as their effect is anti-dilutive.

Nature of Business and Organi33

Nature of Business and Organization (Details) - subsidiary	1 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Reduction in workforce (as a percent)	40.00%
Number of wholly-owned subsidiaries now dissolved		2

Significant Accounting Polici34

Significant Accounting Policies (Details)	12 Months Ended
	Dec. 31, 2017USD ($)segmentTransaction	Dec. 31, 2016USD ($)Transaction
Basis of Presentation
Number of intercompany transactions | Transaction	0	0
Intercompany balances at period end	$ 0	$ 0
Segment Information
Number of Operating Segments | segment	1
Minimum
Property and equipment useful lives
Property, Plant and Equipment, Useful Life	3 years
Maximum
Property and equipment useful lives
Property, Plant and Equipment, Useful Life	7 years
Prepaid Expenses
Research and Development Expense
Capitalized research and development costs	$ 100,000

New Accounting Pronouncements (

New Accounting Pronouncements (Details) - USD ($)	Dec. 31, 2017	Jan. 01, 2017	Dec. 31, 2016
New Accounting Pronouncement or Change in Accounting Principle, Retrospective Adjustments [Abstract]
Deferred tax asset, net operating loss	$ 62,921,000		$ 78,021,000
Valuation allowance for net operating loss deferred tax assets	$ 95,874,000		$ 106,729,000
ASU 2016-09
New Accounting Pronouncement or Change in Accounting Principle, Retrospective Adjustments [Abstract]
Deferred tax asset, net operating loss		$ 800,000
Valuation allowance for net operating loss deferred tax assets		800,000
ASU 2016-09 | Retained Deficit
New Accounting Pronouncement or Change in Accounting Principle, Retrospective Adjustments [Abstract]
Cumulative effective of the adoption of ASU 2016-09		$ (300,000)

Net Loss per Share - antidiluti

Net Loss per Share - antidilutive (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential Common Stock Equivalents, Outstanding	7,987,064	6,880,767	6,290,870
Outstanding common stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential Common Stock Equivalents, Outstanding	5,878,660	6,447,594	5,686,815
Outstanding warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential Common Stock Equivalents, Outstanding	722,000	34,647	34,647
PRSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential Common Stock Equivalents, Outstanding			213,758
RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential Common Stock Equivalents, Outstanding	1,383,770	394,132	351,414
Shares to be purchased under the ESPP
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potential Common Stock Equivalents, Outstanding	2,634	4,394	4,236

Other Comprehensive Income (L37

Other Comprehensive Income (Loss) - components (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	$ 137,147,363	$ 171,346,137	$ 205,004,118
Net amount reclassified to net loss		(1,295)	(47,040)
Balance at end of period	95,484,145	137,147,363	171,346,137
Foreign Currency Translation Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	0	0	(50,592)
Unrealized gain (loss)	0	0	(1,352)
Net amount reclassified to net loss		0	(51,944)
Other comprehensive income (loss)	0	0	50,592
Balance at end of period	0	0	0
Unrealized Net Gains (Losses) on Securities
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(41,196)	(79,399)	(93,336)
Unrealized gain (loss)	(23,237)	36,908	18,841
Net amount reclassified to net loss		(1,295)	4,904
Other comprehensive income (loss)	(23,237)	38,203	13,937
Balance at end of period	(64,433)	(41,196)	(79,399)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at beginning of period	(41,196)	(79,399)	(143,928)
Unrealized gain (loss)	(23,237)	36,908	17,489
Net amount reclassified to net loss		(1,295)	(47,040)
Other comprehensive income (loss)	(23,237)	38,203	64,529
Balance at end of period	$ (64,433)	$ (41,196)	$ (79,399)

Other Comprehensive Income (L38

Other Comprehensive Income (Loss) - Reclassifications (Details) - USD ($)	3 Months Ended							12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Nonoperating Income (Expense), Total	$ 11,000	$ 29,000	$ (30,000)	$ 3,000	$ (25,000)	$ (1,000)	$ (3,000)	$ 12,398	$ (28,461)	$ 51,645
Total reclassifications for the Period									1,295	47,040
Unrealized Net Gains (Losses) on Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications for the Period									1,295	(4,904)
Unrealized Net Gains (Losses) on Securities | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Nonoperating Income (Expense), Total									1,295	(4,904)
Foreign Currency Translation Gains (Losses)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Total reclassifications for the Period									$ 0	51,944
Foreign Currency Translation Gains (Losses) | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Nonoperating Income (Expense), Total										$ 51,944

Investments (Details)

Investments (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash
Cash	$ 2,544,972	$ 6,249,703
Cash equivalents
Cash and cash equivalents at cost	18,559,130	31,228,192
Cash and cash equivalents at carrying value	18,559,130	31,228,192	$ 15,431,622	$ 45,533,443
Short-term Investments
Short-term investments (due within 1 year)
Available-for-sale Securities	78,912,297	106,979,224
Available-for-sale Securities, Amortized Cost Basis	78,976,730	107,020,420
Short-term Investments | U.S. government treasury obligations
Short-term investments (due within 1 year)
Available-for-sale Securities	62,970,115	86,053,755
Available-for-sale Securities, Amortized Cost Basis	63,034,548	86,078,622
Short-term Investments | Corporate obligations
Short-term investments (due within 1 year)
Available-for-sale Securities	15,942,182	20,925,469
Available-for-sale Securities, Amortized Cost Basis	15,942,182	20,941,799
FDIC insured deposits and money market funds
Cash equivalents
Cash equivalents at cost		24,978,489
Cash Equivalents, at Carrying Value		24,978,489
Repurchase Agreements
Cash equivalents
Cash equivalents at cost	10,000,000
Cash Equivalents, at Carrying Value	10,000,000
Money Market Funds
Cash equivalents
Cash equivalents at cost	6,014,158
Cash Equivalents, at Carrying Value	6,014,158
Level 1
Cash
Cash	2,544,972	6,249,703
Cash equivalents
Cash and cash equivalents at carrying value	8,559,130	31,228,192
Level 1 | Short-term Investments
Short-term investments (due within 1 year)
Available-for-sale Securities	62,970,115	86,053,755
Level 1 | Short-term Investments | U.S. government treasury obligations
Short-term investments (due within 1 year)
Available-for-sale Securities	62,970,115	86,053,755
Level 1 | Short-term Investments | Corporate obligations
Short-term investments (due within 1 year)
Available-for-sale Securities	0
Level 1 | FDIC insured deposits and money market funds
Cash equivalents
Cash Equivalents, at Carrying Value		24,978,489
Level 1 | Repurchase Agreements
Cash equivalents
Cash Equivalents, at Carrying Value	0
Level 1 | Money Market Funds
Cash equivalents
Cash Equivalents, at Carrying Value	6,014,158
Level 2
Cash
Cash	0
Cash equivalents
Cash and cash equivalents at carrying value	10,000,000
Level 2 | Short-term Investments
Short-term investments (due within 1 year)
Available-for-sale Securities	15,942,182	20,925,469
Level 2 | Short-term Investments | U.S. government treasury obligations
Short-term investments (due within 1 year)
Available-for-sale Securities	0
Level 2 | Short-term Investments | Corporate obligations
Short-term investments (due within 1 year)
Available-for-sale Securities	15,942,182	$ 20,925,469
Level 2 | Repurchase Agreements
Cash equivalents
Cash Equivalents, at Carrying Value	10,000,000
Level 2 | Money Market Funds
Cash equivalents
Cash Equivalents, at Carrying Value	$ 0

Investments unrealized gains (D

Investments unrealized gains (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Investments, Debt and Equity Securities [Abstract]
Unrealized Gain on Securities	$ 0	$ 8,257
Unrealized Loss on Securities	64,433	49,453
Realized Gain on Securities	0	0
Realized Loss on Securities	$ 0	$ 53

Property and Equipment (Details

Property and Equipment (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 7,362,497	$ 8,457,450
Less accumulated depreciation	(5,180,098)	(5,252,373)
Property, Plant and Equipment, Net	2,182,399	3,205,077
Depreciation, Depletion and Amortization [Abstract]
Depreciation	$ 922,670	919,809	$ 886,710
Maximum
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Useful Life	7 years
Minimum
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Useful Life	3 years
Laboratory equipment
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 5,626,280	6,666,506
Property, Plant and Equipment, Useful Life	7 years
Office equipment and software
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 1,245,232	1,347,768
Office equipment and software | Maximum
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Useful Life	7 years
Office equipment and software | Minimum
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Useful Life	3 years
Leasehold improvements
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 424,176	424,176
Property, Plant and Equipment, Useful Life	7 years
Assets not in service
Property, Plant and Equipment, Net, by Type [Abstract]
Property, Plant and Equipment, Gross	$ 66,809	$ 19,000

Warrants (Details)

Warrants (Details)	Sep. 29, 2017USD ($)item$ / sharesshares	Dec. 31, 2017USD ($)itemshares	Dec. 31, 2016USD ($)	Dec. 31, 2015USD ($)
Class of Warrant or Right [Line Items]
Number of calendar days prior to warrant issue the average closing price of common stock used to determine warrant exercise price	30 days
Proceeds from Warrant Exercises | $		$ 4,556,421	$ 0	$ 0
Expected term of warrants	10 years
Historic volatility used to value the warrants	91.10%
Interest rate assumption used to value the warrants	2.28%
Number of other warrants outstanding | item		0
Common Stock
Class of Warrant or Right [Line Items]
Stock Issued During Period Shares Warrant Exercise		3,278,000
Warrant One
Class of Warrant or Right [Line Items]
Proceeds from Warrant Exercises | $	$ 4,600,000
Warrant One | Common Stock
Class of Warrant or Right [Line Items]
Stock Issued During Period Shares Warrant Exercise	3,278,000
Warrant Two
Class of Warrant or Right [Line Items]
Number of shares into which the remaining warrant could be converted		722,000
License Agreement | ABX
Class of Warrant or Right [Line Items]
Number Of Warrants Issued Per Agreement | item	2
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	4,000,000
Stock Issued During Period Shares Warrant Exercise	3,278,000
License Agreement | ABX | Common Stock
Class of Warrant or Right [Line Items]
Class of Warrant or Right, Exercise Price of Warrants or Rights | $ / shares	$ 1.39
License Agreement | Maximum | ABX
Class of Warrant or Right [Line Items]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	4,000,000
License Agreement | Maximum | ABX | Common Stock
Class of Warrant or Right [Line Items]
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	4,000,000

Leases (Details)

Leases (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Leases [Abstract]
Rent expense for operating leases	$ 749,406	$ 743,323	$ 736,249
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,018	304,523
Total minimum lease payments	$ 304,523

Stockholders' Equity - Issuance

Stockholders' Equity - Issuances Related to the License Agreement (Details)	Oct. 24, 2017shares	Sep. 29, 2017itemshares
Issuances Related to the License Agreement
Number of shares of common stock filed on registration statement per Registration Rights Agreement	6,000,000
License Agreement | ABX
Issuances Related to the License Agreement
Common stock issued per agreement		2,000,000
Number Of Warrants Issued Per Agreement | item		2
Aggregate number of common stock shares that may be purchased by exercise of warrants		4,000,000
Number of warrants exercised | item		1
Stock Issued During Period Shares Warrant Exercise		3,278,000
License Agreement | ABX | Maximum
Issuances Related to the License Agreement
Aggregate number of common stock shares that may be purchased by exercise of warrants		4,000,000

Stockholders' Equity - Stock Op

Stockholders' Equity - Stock Options assumptions (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value Assumptions
Expected volatility		92.98%	98.83%	106.38%
Risk-free interest rate		2.15%	1.47%	1.55%
Weighted-average expected life (in years)		6 years 10 months 24 days	6 years 7 months 6 days	6 years 4 months 24 days
Dividend yield		0.00%	0.00%	0.00%
Value of options granted during period		$ 1,600,031	$ 2,838,053
P. Ron Ellis
Fair Value Assumptions
Additional compensation cost due to modification	$ 2,800,000
1997 And 2007 Plans | Service Based Options
Additional disclosures
Vesting period		4 years
1997 And 2007 Plans | Service Based Options | Service based vesting, first period
Additional disclosures
Vesting period		2 years
Shares that will vest (as a percentage)		0.50%
1997 And 2007 Plans | Performance Based Options
Additional disclosures
Vesting period		4 years
2010 Equity Incentive Plan
Stock-Based Compensation Plans
Shares authorized and reserved		11,850,563	11,003,563
2010 Equity Incentive Plan | Minimum
Additional disclosures
Vesting period		3 years
2010 Equity Incentive Plan | Maximum
Additional disclosures
Vesting period		4 years

Stockholders' Equity - Stock 46

Stockholders' Equity - Stock Option Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value	$ 4,015,344	$ 8,233,220	$ 6,467,294
Unrecognized compensation cost, net of forfeitures	$ 2,100,000	$ 4,200,000
Weighted average period to recognize stock compensation expense	1 year 7 months 6 days	1 year 4 months 24 days
Options
Outstanding, Beginning Balance	6,447,594	5,686,815	5,096,674
Granted during period	883,392	1,100,997	1,126,672
Exercised during period	(378,030)	(129,638)	(146,046)
Expired during period	(716,436)	(28,369)	(156,160)
Forfeited during period	(357,860)	(182,211)	(234,325)
Outstanding, Ending Balance	5,878,660	6,447,594	5,686,815
Weighted-Average Exercise Price
Outstanding, Beginning Balance	$ 6.41	$ 6.87	$ 7.29
Granted during period	2.29	3.21	5.23
Exercised during period	2.88	2.01	2.60
Expired during period	8.02	7.65	11.03
Forfeited during period	4.53	4.45	8.05
Outstanding, Ending Balance	$ 5.93	$ 6.41	$ 6.87
Additional disclosures
Options, Exercisable	4,370,748	4,666,628	3,391,069
Weighted Average Exercise Price, Exercisable	$ 6.79	$ 6.76	$ 6.46
Weighted Average Remaining Contractual Term	5 years 9 months 29 days	6 years 2 months 1 day	6 years 6 months 7 days
Weighted Average Remaining Contractual Term exercisable at end of period	4 years 11 months 1 day	5 years 4 months 2 days	5 years 4 months 13 days
Aggregate Intrinsic Value	$ 3,357,028	$ 33,283	$ 1,432,306
Aggregate Intrinsic Value, exercisable at end of period	$ 1,319,246	$ 33,283	$ 1,333,875

Stockholders' Equity - nonveste

Stockholders' Equity - nonvested stock options (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Options, Nonvested stock options, Beginning Balance	1,780,966	2,295,746	2,401,396
Options, Granted during year	883,392	1,100,997	1,126,672
Options, Vested during year	(798,586)	(1,433,566)	(997,997)
Options, Forfeited during year	(357,860)	(182,211)	(234,325)
Options, Nonvested stock options, Ending Balance	1,507,912	1,780,966	2,295,746
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-Average Grant Date Value, Nonvested stock options, Beginning Balance	$ 4.41	$ 6.05	$ 7.07
Weighted-Average Grant Date Value, Granted during year	1.81	2.58	4.34
Weighted-Average Grant Date Value, Vested during year	5.03	5.74	6.48
Weighted-Average Grant Date Value, Forfeited during year	3.63	3.57	6.37
Weighted-Average Grant Date Value, Nonvested stock options, Ending Balance	$ 2.75	$ 4.41	$ 6.05
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value	$ 635,925	$ 126,651

Stockholders' Equity - Restrict

Stockholders' Equity - Restricted Stock Units (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Stock Units
Unrecognized compensation cost		$ 1.1
Weighted average period to recognize stock compensation expense	1 year 7 months 6 days	1 year 4 months 24 days
RSUs
Restricted Stock Units
Unrecognized compensation cost	$ 5.7
Weighted average period to recognize stock compensation expense	1 year 4 months 24 days	1 year 4 months 24 days
Restricted Stock Units
Outstanding at beginning of period	394,132	351,414	161,439
Granted during period	1,300,068	254,538	260,976
Vested during period	(158,112)	(177,078)	(40,333)
Forfeited during period	(152,318)	(34,742)	(30,668)
Outstanding at the end of the period	1,383,770	394,132	351,414
Weighted-Average Grant Date Fair Value
Outstanding beginning of period	$ 4.96	$ 7.03	$ 11.11
Granted during period	4.90	3.21	5.17
Vested during period	5.35	6.71	11.11
Forfeited during period	3.15	4.13	8.07
Outstanding end of period	$ 5.05	$ 4.96	$ 7.03
RSUs | 2010 Equity Incentive Plan
Restricted Stock Units
Number of shares of common stock to be paid upon vesting of RSU	1
Minimum | 2010 Equity Incentive Plan
Restricted Stock Units
Vesting period	3 years
Maximum | 2010 Equity Incentive Plan
Restricted Stock Units
Vesting period	4 years
Vesting tranche one | RSUs
Restricted Stock Units
Vesting period	2 years
Vesting tranche two | RSUs
Restricted Stock Units
Vesting period	3 years
Vesting tranche three | RSUs
Restricted Stock Units
Vesting period	4 years

Stockholders' Equity - ESPP (De

Stockholders' Equity - ESPP (Details) - Shares to be purchased under the ESPP - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Employee Stock Purchase Plan (Abstract)
Shares available for issuance under ESPP	769,542	825,154
Number of shares purchased under ESPP	55,612
Average purchase price of shares under ESPP	$ 1.30

Income Taxes - Effective rate r

Income Taxes - Effective rate reconciliation (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income tax computed at federal statutory tax rate	34.00%	34.00%	34.00%
State taxes, net of federal benefit	3.60%	3.30%	3.20%
State taxes rate change, net of federal benefit	(60.30%)	0.00%	0.00%
International operations	0.00%	(0.70%)	(4.80%)
Research and development credits	2.90%	4.00%	3.80%
Orphan drug credits	0.30%	0.60%	0.90%
Equity compensation	(1.10%)	(3.70%)	(2.00%)
Tax reform	(60.30%)	0.00%	0.00%
Change in valuation allowance	20.60%	(37.50%)	(35.10%)
Total	0.00%	0.00%	0.00%

Income Taxes - NOLs (Details)

Income Taxes - NOLs (Details)	Dec. 31, 2017USD ($)
Operating Loss Carryforwards [Line Items]
Maximum net operating losses and credit equivalents available for use in 2017	$ 218,700,000
Federal
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	247,493,000
State
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 315,755,000

Income Taxes - Net deferred tax

Income Taxes - Net deferred tax assets and liabilities (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets
Net operating loss carryforwards	$ 62,921,000	$ 78,021,000
Research and development credit carryforwards	16,456,000	14,143,000
Orphan drug credit	7,518,000	7,235,000
Stock options	4,766,000	7,105,000
Intangibles	4,045,000
Other	334,000	562,000
Deferred tax assets	96,040,000	107,066,000
Deferred tax liabilities
Property and equipment	(166,000)	(337,000)
Deferred tax liabilities	(166,000)	(337,000)
Net deferred tax asset before valuation allowance	95,874,000	106,729,000
Less valuation allowance	$ (95,874,000)	$ (106,729,000)

Income Taxes - Unrecognized tax

Income Taxes - Unrecognized tax benefits (Details) - USD ($)	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 2,274,000	$ 3,405,000
Additions based on tax positions related to the current year			$ 3,405,000
Impact of tax reform		(1,131,000)
Balance at end of period		2,274,000	$ 3,405,000
Uncertain tax liabilities that, if recognized, would affect the annual effective tax rate		$ 0
Effect Of Tax Cuts And Jobs Act Of 2017 Accounting Incomplete Provisional [Abstract]
Corporate income tax rate		34.00%	34.00%	34.00%
Forecast
Effect Of Tax Cuts And Jobs Act Of 2017 Accounting Incomplete Provisional [Abstract]
Corporate income tax rate	21.00%

Collaborations and Other Arra54

Collaborations and Other Arrangements - ABX (Details) $ in Millions	Sep. 29, 2017USD ($)itemshares	Jun. 30, 2018person	Mar. 31, 2018person	Dec. 31, 2017USD ($)
Forecast
ABX Development and License Agreement
Number of patients with mCRPC included in study | person		750
Number of mCRPC patients included in phase 2 multi-center trial | person			200
ABX | License Agreement
ABX Development and License Agreement
Upfront cash payment	$ 11.9
Total consideration excluding common stock shares and warrants	$ 12
Stock Issued During Period Shares Asset Acquisition | shares	2,000,000
Number of warrants issued per agreement | item	2
Aggregate number of common stock shares that may be purchased by exercise of warrants | shares	4,000,000
Research And Development In Process Acquired Expense				$ 16.5
Portion of acquired IPRD expense related to the upfront fee paid				12
Portion of acquired IPRD expense related to the fair value of the common stock and warrants issued				3.8
Portion of acquired IPRD expense related to legal and professional fees				$ 0.7
ABX | Maximum | License Agreement
ABX Development and License Agreement
Aggregate number of common stock shares that may be purchased by exercise of warrants | shares	4,000,000
ABX | Achievement Of Regulatory Milestones | Maximum | License Agreement
ABX Development and License Agreement
Potential milestone payments to be paid	$ 25
ABX | Achievement Of Sales Milestones | Maximum | License Agreement
ABX Development and License Agreement
Potential milestone payments to be paid	$ 135

Collaborations and Other Arra55

Collaborations and Other Arrangements - NMP (Details) - NMP - License And Commercialization Agreement $ in Millions	1 Months Ended	53 Months Ended
	Aug. 31, 2013USD ($)item	Dec. 31, 2017USD ($)
NMP License and Commercialization Agreement
Deferred Revenue		$ 0.8
Period of time for termination notice to be given prior to the first commercial sale in Japan	90 days
Period of time for termination notice to be given after the first commercial sale in Japan	6 months
Period of time for termination notice to be given after Company receives regulatory approval in Japan but fails to launch the product	6 months
Up-front Payment Arrangement
NMP License and Commercialization Agreement
Upfront payment received	$ 1
Achievement Of Regulatory Milestones
NMP License and Commercialization Agreement
Milestone revenue recognized		$ 0
Achievement Of Regulatory Goals For Etarfolatide In Five Different Cancer Indications Milestone
NMP License and Commercialization Agreement
Number of cancer indications requiring achievement of regulatory goals | item	5
Achievement Of Regulatory Goals For Etarfolatide In Five Different Cancer Indications Milestone | Maximum
NMP License and Commercialization Agreement
Potential milestone payment	$ 4.5
Commencement Of Clinical Trials In Japan For Specific And Nonspecific Indications And Filing For Approval In Japan For Specific And Nonspecific Indications Milestone | Maximum
NMP License and Commercialization Agreement
Potential milestone payment	$ 4.5

Collaborations and Other Arra56

Collaborations and Other Arrangements - Other (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Mar. 01, 2010	Oct. 31, 2007	Dec. 31, 1995
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Penalties or milestone payments accrued or paid	$ 0	$ 0
R & D Biopharmaceuticals | License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Annual maintenance fees				$ 25,000
R & D Biopharmaceuticals | License Agreement | Research and Development Expense.
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront fee paid				300,000
R & D Biopharmaceuticals | License Agreement | Achievement Of Specific Scientific Clinical And Regulatory Milestones [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments to be paid				$ 5,900,000
Purdue Research Foundation | License Agreement
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Minimum annual royalty payments due prior to commercial sales of product			$ 15,000		$ 12,500
Minimum annual royalty payments due after commercial sales of product begin			100,000
Purdue Research Foundation | License Agreement | Approval Of New Drug Application In US Milestone
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Potential milestone payments to be paid			$ 500,000

Related-Party Transactions (Det

Related-Party Transactions (Details) - USD ($)	1 Months Ended	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2011
Related Party Transaction [Line Items]
Research and Development Expense		$ 5,128,000	$ 4,090,000	$ 8,655,000	$ 7,994,000	$ 8,188,000	$ 5,985,000	$ 6,788,000	$ 6,531,000	$ 25,866,845	$ 27,492,185	$ 26,309,475
Operating Leases, Rent Expense, Net, Total										749,406	743,323	736,249
Purdue University And Purdue Research Foundation [Member]
Related Party Transaction [Line Items]
Accounts Payable and Other Accrued Liabilities		$ 29,600								29,600
Purdue University [Member]
Related Party Transaction [Line Items]
Research and Development Expense										781,000	1,069,000	1,000,000
Purdue Research Foundation
Related Party Transaction [Line Items]
Operating Leases, Rent Expense, Net, Total										609,000	597,000	588,000
On Target
Related Party Transaction [Line Items]
Proceeds from License Fees Received	$ 191,000
License and Maintenance Revenue										20,000	20,000	20,000
Research and Development Expense. | On Target
Related Party Transaction [Line Items]
Reimbursement Revenue										$ 6,349	$ 14,397	$ 21,044
Patents [Member] | On Target
Related Party Transaction [Line Items]
Reimbursement Revenue													$ 50,000

Retirement Plans (Details)

Retirement Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 0.3	$ 0.3	$ 0.3

Restructuring Costs (Details)

Restructuring Costs (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Costs
Reduction in workforce (as a percent)	40.00%
Restructuring expense		$ 2,300,000
Accrual balance		(106,900)
Restructuring Reserve [Roll Forward]
Charges during the period		2,103,000
Revised estimates during the period		(30,000)
Amounts paid during the period		(1,966,100)
Balance at end of period		106,900
Proceed Trial Termination
Restructuring Costs
Accrual balance		0	$ (46,600)	$ 1,300,000
Restructuring Reserve [Roll Forward]
Balance at beginning of period		0	46,600	(1,300,000)
Revised estimates during the period			(15,800)	134,000
Amounts paid during the period			(30,800)	(1,387,400)
Balance at end of period			$ 0	$ 46,600
Employee Termination Accrual
Restructuring Reserve [Roll Forward]
Charges during the period		1,029,400
Amounts paid during the period		(1,029,400)
EC1456 Phase 1 Trial Termination Accrual
Restructuring Costs
Accrual balance		(106,900)
Restructuring Reserve [Roll Forward]
Charges during the period		947,100
Revised estimates during the period		(30,000)
Amounts paid during the period		(810,200)
Balance at end of period		106,900
Other Restructuring Costs Accrual
Restructuring Reserve [Roll Forward]
Charges during the period		126,500
Amounts paid during the period		(126,500)
General and Administrative Expense
Restructuring Costs
Employee termination benefits		100,000
Research and Development Expense.
Restructuring Costs
Employee termination benefits		900,000
Remaining EC1456 phase 1b trial expenses, including site close-out expenses		900,000
Other restructuring expenses		300,000
Fixed asset impairment		$ 100,000

Selected Quarterly Financial 60

Selected Quarterly Financial Data (unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Information [Abstract]
Revenues	$ 12,000	$ 33,000	$ 13,000	$ 12,000	$ 12,000	$ 33,000	$ 13,000	$ 12,000	$ 70,000	$ 70,000	$ 70,000
Operating Expenses [Abstract]
Research and development	5,128,000	4,090,000	8,655,000	7,994,000	8,188,000	5,985,000	6,788,000	6,531,000	25,866,845	27,492,185	26,309,475
General and administrative	3,708,000	3,011,000	3,306,000	3,745,000	3,096,000	2,988,000	7,394,000	3,820,000	13,769,853	17,298,139	15,733,462
Acquired in-process research and development	46,000	16,493,000							16,539,347	0	0
Loss from operations	(8,870,000)	(23,561,000)	(11,948,000)	(11,727,000)	(11,272,000)	(8,940,000)	(14,169,000)	(10,339,000)	(56,106,045)	(44,720,324)	(41,972,937)
Interest income, net	295,000	265,000	234,000	235,000	232,000	232,000	208,000	189,000	1,029,497	861,212	651,543
Other expense, net	11,000	29,000	(30,000)	3,000	(25,000)		(1,000)	(3,000)	12,398	(28,461)	51,645
Net loss	$ (8,564,000)	$ (23,267,000)	$ (11,744,000)	$ (11,489,000)	$ (11,065,000)	$ (8,708,000)	$ (13,962,000)	$ (10,153,000)	$ (55,064,150)	$ (43,887,573)	$ (41,269,749)
Net loss per share -basic and diluted (in dollars per share)	$ (0.18)	$ (0.55)	$ (0.28)	$ (0.27)	$ (0.26)	$ (0.21)	$ (0.33)	$ (0.24)	$ (1.25)	$ (1.04)	$ (0.98)
Weighted average common shares outstanding - basic and diluted (in shares)	47,979,127	42,636,567	42,503,584	42,434,709	42,289,453	42,263,311	42,178,537	42,109,828	43,900,257	42,210,643	41,939,504