Inovio Pharmaceuticals (INO) 10-K12 Mar 192018 FY Annual reportFinancial data

Company Profile

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
Document and Entity Information - USD ($)	Dec. 31, 2018	Mar. 08, 2019	Jun. 30, 2018
Document and Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Entity Registrant Name	INOVIO PHARMACEUTICALS, INC.
Entity Central Index Key	0001055726
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		97,636,364
Entity Well-known Seasoned Issuer	No
Entity Public Float			$ 335,998,116
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 23,693,633	$ 23,786,579
Short-term investments	57,538,852	103,638,844
Accounts receivable	3,316,361	6,003,205
Accounts receivable from affiliated entities	738,583	486,619
Prepaid expenses and other current assets	1,406,590	2,600,906
Prepaid expenses and other current assets from affiliated entities	1,120,805	1,846,007
Total current assets	87,814,824	138,362,160
Fixed assets, net	15,949,014	18,320,176
Investment in affiliated entity - GeneOne	6,381,926	9,069,401
Investment in affiliated entity - PLS	3,023,987	2,325,079
Intangible assets, net	4,760,145	6,009,729
Goodwill	10,513,371	10,513,371
Other assets	2,669,998	2,639,354
Total assets	131,113,265	187,239,270
Current liabilities:
Accounts payable and accrued expenses	23,134,733	23,278,798
Accounts payable and accrued expenses due to affiliated entities	977,792	926,943
Accrued clinical trial expenses	5,671,764	8,611,892
Common stock warrants	0	360,795
Deferred revenue	223,577	1,175,353
Deferred revenue from affiliated entities	33,575	174,110
Deferred rent	1,065,387	877,535
Deferred grant funding	4,165,848	0
Deferred grant funding from affiliated entities	27,083	0
Total current liabilities	35,299,759	35,405,426
Deferred revenue, net of current portion	150,793	215,853
Deferred rent, net of current portion	8,518,207	9,104,416
Deferred tax liabilities	24,766	24,766
Other liabilities	87,333	0
Total liabilities	44,080,858	44,750,461
Commitments and contingencies
Inovio Pharmaceuticals, Inc. stockholders’ equity:
Preferred stock—par value $0.001; Authorized shares: 10,000,000, issued and outstanding shares: 23 at December 31, 2018 and December 31, 2017	0	0
Common stock—par value $0.001; Authorized shares: 600,000,000 at December 31, 2018 and December 31, 2017, issued and outstanding: 97,225,810 at December 31, 2018 and 90,357,644 at December 31, 2017	97,226	90,358
Additional paid-in capital	707,794,215	665,775,504
Accumulated deficit	(620,426,436)	(523,356,317)
Accumulated other comprehensive loss	(528,867)	(117,005)
Total Inovio Pharmaceuticals, Inc. stockholders’ equity	86,936,138	142,392,540
Non-controlling interest	96,269	96,269
Total stockholders’ equity	87,032,407	142,488,809
Total liabilities and stockholders’ equity	$ 131,113,265	$ 187,239,270

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value ($ per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (shares)	10,000,000	10,000,000
Preferred stock, shares issued (shares)	23	23
Preferred stock, shares outstanding (shares)	23	23
Common stock, par value ($ per share)	$ 0.001	$ 0.001
Common stock, shares authorized (shares)	600,000,000	600,000,000
Common stock, shares issued (shares)	97,225,810	90,357,644
Common stock, shares (shares)	97,225,810	90,357,644

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($)	3 Months Ended								12 Months Ended
Consolidated Statements of Operations - USD ($)	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Total revenues	$ 2,502,624	$ 2,000,868	$ 24,448,761	$ 1,529,644	$ 8,787,234	$ 2,644,543	$ 20,412,124	$ 10,376,185	$ 30,481,897	$ 42,220,086	$ 35,368,361
Operating expenses:
Research and development	26,365,647	21,851,858	22,462,620	24,577,751	24,641,124	25,510,239	23,878,751	24,542,504	95,257,876	98,572,618	88,712,035
General and administrative	5,636,141	6,791,693	7,189,310	9,698,015	8,033,899	6,319,775	6,169,106	7,767,589	29,315,159	28,290,369	23,892,263
Gain on sale of assets					(1,000,000)	0	0	0	0	(1,000,000)	(1,000,000)
Total operating expenses	32,001,788	28,643,551	29,651,930	34,275,766	31,675,023	31,830,014	30,047,857	32,310,093	124,573,035	125,862,987	111,604,298
Loss from operations	(29,499,164)	(26,642,683)	(5,203,169)	(32,746,122)	(22,887,789)	(29,185,471)	(9,635,733)	(21,933,908)	(94,091,138)	(83,642,901)	(76,235,937)
Other income (expense):
Interest and other income, net	(169,300)	380,987	396,681	312,523	509,266	463,346	300,021	340,341	920,891	1,612,974	1,257,257
Change in fair value of common stock warrants	0	228,665	259,971	(127,841)	579,546	423,296	(312,500)	116,477	360,795	806,819	127,554
Gain (loss) on investment in affiliated entity	(3,293,741)	1,017,359	(2,092,608)	2,380,423	292,798	(5,835,741)	169,096	(1,608,817)	(1,988,567)	(6,982,664)	1,110,787
Net loss before provision for income tax	(32,962,205)	(25,015,672)	(6,639,125)	(30,181,017)					(94,798,019)	(88,205,772)	(73,740,339)
Provision for income taxes	0	0	0	(2,169,811)					(2,169,811)	0	0
Net loss	$ (32,962,205)	$ (25,015,672)	$ (6,639,125)	$ (32,350,828)	$ (21,506,179)	$ (34,134,570)	$ (9,479,116)	$ (23,085,907)	$ (96,967,830)	$ (88,205,772)	$ (73,740,339)
Net loss per share
Basic ($ per share)	$ (0.34)	$ (0.27)	$ (0.07)	$ (0.36)	$ (0.24)	$ (0.39)	$ (0.13)	$ (0.31)	$ (1.05)	$ (1.08)	$ (1.01)
Diluted ($ per share)	$ (0.34)	$ (0.27)	$ (0.08)	$ (0.36)	$ (0.24)	$ (0.40)	$ (0.13)	$ (0.31)	$ (1.05)	$ (1.09)	$ (1.01)
Weighted average number of common shares outstanding
Basic (shares)									92,539,997	81,777,493	73,214,766
Diluted (shares)									92,539,997	81,918,022	73,214,766
Grants and miscellaneous revenue from affiliated entity
Revenues:
Total revenues					$ 171,091	$ 707,922	$ 1,079,282	$ 614,036	$ 0	$ 2,572,331	$ 340,563
Grants and miscellaneous revenue
Revenues:
Total revenues	$ 73,817	$ 2,591	$ 2,590	$ 92,590	980,443	1,456,216	2,797,647	5,240,233	171,588	10,474,539	27,136,457
Revenue under collaborative research and development arrangements with affiliated entity
Revenues:
Total revenues	56,207	184,990	60,319	148,008	226,486	129,133	176,879	233,330	449,524	765,828	1,400,594
Revenue under collaborative research and development arrangements
Revenues:
Total revenues	$ 2,372,600	$ 1,813,287	$ 24,385,852	$ 1,289,046	$ 7,409,214	$ 351,272	$ 16,358,316	$ 4,288,586	$ 29,860,785	$ 28,407,388	$ 6,490,747

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss - USD ($)	12 Months Ended
Consolidated Statements of Comprehensive Loss - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Comprehensive Income [Abstract]
Net loss	$ (96,967,830)	$ (88,205,772)	$ (73,740,339)
Other comprehensive income (loss):
Unrealized loss on investment in affiliated entity, net of tax	0	(1,452,431)	(1,268,404)
Unrealized gain (loss) on short-term investments, net of tax	(180,496)	7,458	(111,967)
Comprehensive loss	$ (97,148,326)	$ (89,650,745)	$ (75,120,710)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($)	Total	Preferred stock	Common stock	Additional paid-in capital	Accumulated deficit	Accumulated other comprehensive income (loss)	Non- controlling interest
Beginning balance (shares) at Dec. 31, 2015		23	72,217,965
Beginning balance at Dec. 31, 2015	$ 175,933,053	$ 0	$ 72,218	$ 534,004,564	$ (361,097,896)	$ 2,708,339	$ 245,828
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for cash, net of financing costs (shares)			658,748
Issuance of common stock for cash, net of financing costs	6,295,761		$ 659	6,295,102
Issuance of common stock for Bioject acquisition (shares)			440,122
Issuance of common stock for Bioject acquisition	4,300,000		$ 440	4,299,560
Payment to minority stockholders	(149,559)						(149,559)
Exercise of stock options and warrants for cash and vesting of RSUs, net of tax payments (shares)			450,045
Exercise of stock options and warrants for cash and vesting of RSUs, net of tax payments	1,640,740		$ 449	1,640,291
Cashless exercise of stock options and warrants (shares)			295,490
Cashless exercise of stock options and warrants	0		$ 296	(296)
Stock-based compensation	10,479,135			10,479,135
Net loss attributable to common stockholders	(73,740,339)				(73,740,339)
Unrealized gain (loss) on short-term investments, net of tax	(111,967)					(111,967)
Unrealized loss on investment in affiliated entity, net of tax	(1,268,404)					(1,268,404)
Ending balance (shares) at Dec. 31, 2016		23	74,062,370
Ending balance at Dec. 31, 2016	123,378,420	$ 0	$ 74,062	556,718,356	(434,838,235)	1,327,968	96,269
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for cash, net of financing costs (shares)			15,437,406
Issuance of common stock for cash, net of financing costs	94,347,922		$ 15,437	94,332,485
Exercise of stock options and warrants for cash and vesting of RSUs, net of tax payments (shares)			857,868
Exercise of stock options and warrants for cash and vesting of RSUs, net of tax payments	1,342,250		$ 859	1,341,391
Stock-based compensation	13,070,962			13,070,962
Net loss attributable to common stockholders	(88,205,772)				(88,205,772)
Unrealized gain (loss) on short-term investments, net of tax	7,458					7,458
Unrealized loss on investment in affiliated entity, net of tax	(1,452,431)					(1,452,431)
Ending balance (shares) at Dec. 31, 2017		23	90,357,644
Ending balance at Dec. 31, 2017	142,488,809	$ 0	$ 90,358	665,775,504	(523,356,317)	(117,005)	96,269
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock for cash, net of financing costs (shares)			5,669,025
Issuance of common stock for cash, net of financing costs	29,227,776		$ 5,669	29,222,107
Exercise of stock options and warrants for cash and vesting of RSUs, net of tax payments (shares)			1,199,141
Exercise of stock options and warrants for cash and vesting of RSUs, net of tax payments	1,809,526		$ 1,199	1,808,327
Stock-based compensation	10,654,622			10,988,277	(333,655)
Net loss attributable to common stockholders	(96,967,830)				(96,967,830)
Unrealized gain (loss) on short-term investments, net of tax	(180,496)					(180,496)
Unrealized loss on investment in affiliated entity, net of tax	0
Ending balance (shares) at Dec. 31, 2018		23	97,225,810
Ending balance at Dec. 31, 2018	$ 87,032,407	$ 0	$ 97,226	$ 707,794,215	$ (620,426,436)	$ (528,867)	$ 96,269

Consolidated Statements of St_2

Consolidated Statements of Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Stockholders' Equity [Abstract]
Issuance of common stock for cash, financing costs	$ 0	$ 4,900	$ 128

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($)	12 Months Ended
Consolidated Statements of Cash Flows - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net loss	$ (96,967,830)	$ (88,205,772)	$ (73,740,339)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	3,747,183	1,850,376	1,708,498
Amortization of intangible assets	1,249,584	1,618,665	1,377,466
Change in value of common stock warrants	(360,795)	(806,819)	(127,554)
Stock-based compensation	10,654,622	13,070,962	10,479,135
Amortization of premiums on investments	72,561	319,845	266,290
Deferred taxes	0	(150,027)	(849)
Loss on short-term investments	1,342,005	215,423	139,249
Loss on disposal of fixed assets	14,529	0	0
Loss (gain) on investment in affiliated entities	1,988,567	6,982,664	(1,110,787)
Gain on sale of intangible assets	0	(1,000,000)	(1,000,000)
Changes in operating assets and liabilities:
Accounts receivable	2,686,844	9,818,306	(8,521,899)
Accounts receivable from affiliated entities	(251,964)	261,736	(714,908)
Prepaid expenses and other current assets	1,194,316	(851,847)	(831,802)
Prepaid expenses and other current assets from affiliated entities	725,202	(333,583)	(901,772)
Other assets	(30,644)	(526,207)	(1,442,314)
Accounts payable and accrued expenses	550,407	2,829,807	6,367,965
Accrued clinical trial expenses	(2,940,128)	2,243,503	3,767,906
Accounts payable and accrued expenses due to affiliated entities	50,849	(145,636)	907,532
Deferred revenue	(1,016,836)	(13,689,322)	1,527,686
Deferred revenue from affiliated entities	(140,535)	(319,876)	(687,827)
Deferred rent	(398,357)	3,608,881	(16,728)
Deferred grant funding	4,165,848	0	0
Deferred grant funding from affiliated entities	27,083	0	0
Other liabilities	87,333	0	0
Net cash used in operating activities	(73,550,156)	(63,208,921)	(62,555,052)
Cash flows from investing activities:
Purchases of investments	(88,155,046)	(95,700,144)	(57,317,671)
Maturities of investments	132,659,976	77,162,902	76,528,030
Purchases of capital assets	(2,085,022)	(10,293,902)	(2,738,470)
Proceeds from sale of intangible assets	0	1,000,000	1,000,000
Purchase of intangible and other assets	0	0	(1,200,000)
Net cash provided by (used in) investing activities	42,419,908	(27,831,144)	16,271,889
Cash flows from financing activities:
Proceeds from issuance of common stock and warrants, net of issuance costs	29,227,776	94,347,922	6,295,761
Proceeds from stock option and warrant exercises, net of tax payments	1,809,526	1,342,250	1,640,740
Expenses from other financing activities	0	0	(149,559)
Net cash provided by financing activities	31,037,302	95,690,172	7,786,942
Increase (decrease) in cash and cash equivalents	(92,946)	4,650,107	(38,496,221)
Cash and cash equivalents, beginning of period	23,786,579	19,136,472	57,632,693
Cash and cash equivalents, end of period	23,693,633	23,786,579	19,136,472
Supplemental disclosure of non-cash activities
Common stock issued for purchase of Bioject	0	0	4,300,000
Change in amounts accrued for purchases of property and equipment	694,472	851,204	164,923
Lease incentive recorded as fixed assets and deferred rent	$ 0	$ 0	$ 523,856

The Company

The Company	12 Months Ended
The Company	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
The Company	The Company Inovio Pharmaceuticals, Inc. (the “Company” or “Inovio”), is a late-stage biotechnology company focused on the discovery, development, and commercialization of DNA-based immunotherapies and vaccines that transform the treatment and prevention of cancers and infectious diseases. The Company's DNA-based immunotherapies and vaccines, in combination with its proprietary, efficacy-enabling delivery devices, are intended to generate robust immune responses, in particular functional CD8+ killer T cells and antibodies, to fight target diseases. Inovio’s synthetic products are based on its SynCon ® immunotherapy design. The Company and its collaborators are currently conducting or planning clinical programs of its proprietary SynCon ® immunotherapies for HPV-caused pre-cancers, including cervical, vulvar, and anal dysplasia; HPV-caused cancers, including head & neck, cervical, anal, penile, vulvar, and vaginal; bladder cancer; glioblastoma multiforme ("GBM"); hepatitis B virus; hepatitis C virus; HIV; Ebola; Middle East Respiratory Syndrome, or MERS; Lassa fever; and Zika virus. The Company's partners and collaborators include MedImmune, the global biologics research and development arm of AstraZeneca ("AstraZeneca"), The Wistar Institute, University of Pennsylvania, GeneOne Life Science Inc. ("GeneOne"), ApolloBio Corporation, Regeneron Pharmaceuticals, Inc., Genentech, Inc., Plumbline Life Sciences, Inc., Drexel University, National Institute of Allergy and Infectious Diseases (“NIAID”), United States Military HIV Research Program, U.S. Army Medical Research Institute of Infectious Diseases, National Institutes of Health, HIV Vaccines Trial Network, Defense Advanced Research Projects Agency (“DARPA”), Parker Institute for Cancer Immunotherapy, and Coalition for Epidemic Preparedness Innovations (“CEPI”). Inovio was incorporated in Delaware in June 2001 and has its principal executive offices in Plymouth Meeting, Pennsylvania.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
Summary of Significant Accounting Policies	Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation Inovio incurred a net loss attributable to common stockholders of $97.0 million for the year ended December 31, 2018 . Inovio had working capital of $52.5 million and an accumulated deficit of $620.4 million as of December 31, 2018 . The Company has incurred losses in each year since its inception and expects to continue to incur significant expenses and operating losses for the foreseeable future in connection with the research and preclinical and clinical development of its product candidates. In the first quarter of 2019, the Company received net proceeds of $75.8 million from a private placement of $78.5 million aggregate principal amount of its 6.50% convertible senior notes due 2024 (the “Notes”). These proceeds, in addition to the Company’s cash, cash equivalents and short-term investments of $ 81.2 million and long-term investments of $ 9.4 million as of December 31, 2018, are sufficient to support the Company's operations for a period of at least 12 months from the date it issued these financial statements. In addition, the Company could sell up to an additional $71.8 million in shares of its common stock under its At-the-Market Equity Offering Sales Agreement (the “Sales Agreement”), subject to certain conditions set forth in the Sales Agreement. In order to continue to fund future research and development activities, the Company will need to seek additional capital. This may occur through strategic alliance and licensing arrangements and/or future public or private debt or equity financings including use of its Sales Agreement. Although the Company has a history of equity financings including the receipt of net proceeds of $29.2 million under the current Sales Agreement and a prior agreement during the year ended December 31, 2018 and net proceeds of $94.3 million from an underwritten public offering and a previous at-the-market sales facility during the year ended December 31, 2017 , sufficient funding may not be available, or if available, may be on terms that significantly dilute or otherwise adversely affect the rights of existing stockholders. If adequate funds are not available in the future, the Company may need to delay, reduce the scope of or put on hold one or more of its clinical and/or preclinical programs. The Company’s ability to continue its operations is dependent upon its ability to obtain additional capital in the future and achieve profitable operations. The Company expects to continue to rely on outside sources of financing to meet its capital needs and the Company may never achieve positive cash flow. These consolidated financial statements do not include any adjustments to the specific amounts and classifications of assets and liabilities, which might be necessary should Inovio be unable to continue as a going concern. Inovio’s consolidated financial statements as of and for the year ended December 31, 2018 have been prepared on a going concern basis, which contemplates the realization of assets and the settlement of liabilities and commitments in the normal course of business for the foreseeable future. The Company has evaluated subsequent events after the balance sheet date through the date it issued these financial statements. Consolidation These consolidated financial statements include the accounts of Inovio Pharmaceuticals, Inc. and its subsidiaries. The Company consolidates its wholly-owned subsidiaries Genetronics, Inc., VGX Pharmaceuticals Inc. ("VGX"), and Geneos Therapeutics, Inc. ("Geneos"), and records a non-controlling interest for 15% of VGX Animal Health, Inc., a subsidiary of VGX. All intercompany accounts and transactions have been eliminated upon consolidation. Subsequent to December 31, 2018, Geneos is no longer a wholly owned subsidiary. See Note 18 for additional information. Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one segment operating primarily within the United States. Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosures of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates. Concentration of Credit Risk Financial instruments, that potentially subject the Company to concentrations of credit risk consist primarily of cash and short-term investments. The Company limits its exposure to credit loss by placing its cash and investments with high credit quality financial institutions. Additionally, the Company has established guidelines regarding diversification of its investments and their maturities which are designed to maintain principal and maximize liquidity. The Company has contracts with certain of its customers that have represented more than 10% of the Company's total revenues, as discussed in Note 7. Fair value of Financial Instruments The Company’s financial instruments consist principally of cash equivalents, short-term investments and investments in affiliated entities. The carrying amounts of cash equivalents approximate the related fair values due to the short-term maturities of these instruments. Investments are recorded at fair value, based on current market valuations. After the adoption of ASU No. 2016-01 on January 1, 2018, unrealized gains and losses on the Company's equity investment in its affiliated entity Plumbline Life Sciences, Inc. ("PLS") are reported in the consolidated statement of operations as a gain (loss) on investment in affiliated entities, as discussed below in "Recent Accounting Pronouncements - Recently Adopted." The Company’s investment in GeneOne, an affiliated entity, is accounted for at fair value on a recurring basis, with changes in fair value recorded on the consolidated statements of operations within gain (loss) from investment in affiliated entity. Cash and Cash Equivalents Cash equivalents are considered by the Company to be highly liquid investments purchased with original maturities of three months or less from the date of purchase. Cash and cash equivalents included certain money market accounts at December 31, 2018 and 2017 . Investments The Company defines investments as income-yielding securities that can be readily converted into cash or equity investments classified as available-for-sale. Investments included mutual funds. United States corporate debt securities and equity investments in the Company’s affiliated entities, PLS and GeneOne at December 31, 2018 . Investments included mutual funds, United States corporate debt securities and an equity investment in the Company's affiliated entity PLS at December 31, 2017 . Accounts Receivable Accounts receivable are recorded at invoiced amounts and do not bear interest. The Company performs ongoing credit evaluations of its customers’ financial condition. Credit is extended to customers as deemed necessary and generally does not require collateral. Management believes that the risk of loss is significantly reduced due to the quality and financial position of the Company's customers. No allowance for doubtful accounts was deemed necessary at December 31, 2018 and 2017 . Fixed Assets Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful life of the assets, generally three to five years. Leasehold improvements are amortized over the shorter of the remaining term of the related leases or the estimated economic useful lives of the improvements. Repairs and maintenance are expensed as incurred. Long-Lived Assets All long-lived assets are reviewed for impairment in value when changes in circumstances dictate, based upon undiscounted future operating cash flows, and appropriate losses are recognized and reflected in current earnings, to the extent the carrying amount of an asset exceeds its estimated fair value determined by the use of appraisals, discounted cash flow analyses or comparable fair values of similar assets. The Company has not recognized any losses on long-lived assets through December 31, 2018 and 2017. Valuation of Intangible Assets and Goodwill Intangible assets are amortized over their estimated useful lives ranging from two to 18 years. Acquired intangible assets are continuously being developed for the future economic viability contemplated at the time of acquisition. The Company is concurrently conducting preclinical studies and clinical trials using the acquired intangibles and has entered into licensing agreements for the use of these acquired intangibles. Historically, the Company has recorded patents at cost and amortized these costs using the straight-line method over the expected useful lives of the patents or 17 years, whichever is less. Patent cost consists of the consideration paid for patents and related legal costs. Effective as of the acquisition of VGX in 2009, all new patent costs are expensed as incurred, with patent costs capitalized as of that date continuing to be amortized over the expected life of the patent. License costs are recorded based on the fair value of consideration paid and are amortized using the straight-line method over the shorter of the expected useful life of the underlying patents or the term of the related license agreement to the extent the license has an alternative future use. As of December 31, 2018 and 2017 , the Company’s intangible assets resulting from the acquisition of VGX, as well as the acquisitions of two other companies, Inovio AS and Bioject Medical Technologies, Inc. ("Bioject"), and additional intangibles including previously capitalized patent costs and license costs, net of accumulated amortization, totaled $4.8 million and $ 6.0 million , respectively. The determination of the value of intangible assets requires management to make estimates and assumptions that affect the Company’s consolidated financial statements. The Company assesses potential impairments to intangible assets when there is evidence that events or changes in circumstances indicate that the carrying amount of an asset may not be recovered. The Company’s judgments regarding the existence of impairment indicators and future cash flows related to intangible assets are based on operational performance of its acquired businesses, market conditions and other factors. If impairment is indicated, the Company will reduce the carrying value of the intangible asset to fair value. While current and historical operating and cash flow losses are potential indicators of impairment, the Company believes the future cash flows to be received from its intangible assets will exceed the intangible assets’ carrying value, and accordingly, the Company has not recognized any impairment losses through December 31, 2018 . Goodwill represents the excess of acquisition cost over the fair value of the net assets of acquired businesses. Goodwill is reviewed for impairment at least annually at November 30, or more frequently if an event occurs indicating the potential for impairment. During its goodwill impairment review, the Company may assess qualitative factors to determine whether it is more likely than not that the fair value of its reporting unit is less than its carrying amount, including goodwill. The qualitative factors include, but are not limited to, macroeconomic conditions, industry and market considerations, and the overall financial performance of the Company. If, after assessing the totality of these qualitative factors, the Company determines that it is not more likely than not that the fair value of its reporting unit is less than its carrying amount, then no additional assessment is deemed necessary. Otherwise, the Company proceeds to perform the two-step test for goodwill impairment. The first step involves comparing the estimated fair value of the reporting unit with its carrying value, including goodwill. If the carrying amount of the reporting unit exceeds its fair value, the Company performs the second step of the goodwill impairment test to determine the amount of loss, which involves comparing the implied fair value of the goodwill to the carrying value of the goodwill. The Company may also elect to bypass the qualitative assessment in a period and elect to proceed to perform the first step of the goodwill impairment test. The Company performed its annual assessment for goodwill impairment as of November 30, 2018 , identifying no impairment. Although there are inherent uncertainties in this assessment process, the estimates and assumptions the Company is using are consistent with its internal planning. If these estimates or their related assumptions change in the future, the Company may be required to record an impairment charge on all or a portion of its goodwill and intangible assets. Furthermore, the Company cannot predict the occurrence of future impairment triggering events nor the impact such events might have on its reported asset values. Future events could cause the Company to conclude that impairment indicators exist and that goodwill or other intangible assets associated with its acquired businesses are impaired. Any resulting impairment loss could have an adverse impact on the Company’s results of operations. See Note 9 for further discussion of the Company’s goodwill and intangible assets. Income Taxes The Company recognizes deferred tax assets and liabilities for temporary differences between the financial reporting basis and the tax basis of the Company’s assets and liabilities along with net operating loss and tax credit carry forwards. The Company records a valuation allowance against its deferred tax assets to reduce the net carrying value to an amount that it believes is more likely than not to be realized. When the Company establishes or reduces the valuation allowance against its deferred tax assets, its provision for income taxes will increase or decrease, respectively, in the period such determination is made. Valuation allowances against the Company’s deferred tax assets were $115.0 million and $94.0 million at December 31, 2018 and 2017 , respectively. Changes in the valuation allowances, when they are recognized in the provision for income taxes, are included as a component of the estimated annual effective tax rate. Revenue Recognition Effective January 1, 2018, the Company adopted Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (“Topic 606”) using the modified retrospective method which consisted of applying and recognizing the cumulative effect of Topic 606 at the date of initial application. Topic 606 supersedes the revenue recognition requirements in Accounting Standards Codification (“ASC”) Topic 605, Revenue Recognition (“Topic 605”), including most industry-specific revenue recognition guidance throughout the Industry Topics of the ASC. All periods prior to the adoption date of Topic 606 have not been restated to reflect the impact of the adoption of Topic 606, but continue to be accounted for and presented under Topic 605. The following paragraphs in this section describe the Company's revenue recognition accounting policies under Topic 606 upon adoption on January 1, 2018. Refer to Note 2 to the consolidated financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017 for revenue recognition accounting policies under Topic 605. The Company recognizes revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which it expects to be entitled in exchange for those goods or services. To determine revenue recognition for contracts with customers, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies its performance obligations. At contract inception, the Company assesses the goods or services agreed upon within each contract and assess whether each good or service is distinct and determine those that are performance obligations. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Collaborative Arrangements The Company enters into collaborative arrangements with partners that typically include payment of one or more of the following: (i) license fees; (ii) milestone payments related to the achievement of developmental, regulatory, or commercial goals; and (iii) royalties on net sales of licensed products. Where a portion of non-refundable, upfront fees or other payments received are allocated to continuing performance obligations under the terms of a collaborative arrangement, they are recorded as deferred revenue and recognized as revenue when (or as) the underlying performance obligation is satisfied. As part of the accounting for these arrangements, the Company must develop estimates and assumptions that require judgment of management to determine the underlying stand-alone selling price for each performance obligation which determines how the transaction price is allocated among the performance obligation. The standalone selling price may include items such as forecasted revenues, development timelines, discount rates and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if it can be satisfied at a point in time or over time. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price. License Fees If a license to intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company will recognize revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company will utilize judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments At the inception of each arrangement that includes milestone payments (variable consideration), the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company's or its collaboration partner’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achieving such milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license, collaboration or other revenues and earnings in the period of adjustment. Royalties For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its collaborative arrangements. Under certain collaborative arrangements, the Company has been reimbursed for a portion of its research and development ("R&D") expenses, including costs of drug supplies. When these R&D services are performed under a reimbursement or cost sharing model with its collaboration partner, the Company records these reimbursements as a reduction of R&D expense in its consolidated statements of operations. Grants The Company has determined that as of January 1, 2018, accounting for the Company’s various grant agreements falls under the contributions guidance under Subtopic 958-605, Not-for-Profit Entities-Revenue Recognition , which is outside the scope of Topic 606, as the government agencies granting the Company funds are not receiving reciprocal value for their contributions. Beginning on January 1, 2018, all contributions received from current grant agreements are recorded as a contra expense as opposed to revenue on the consolidated statement of operations. Research and Development Expenses The Company’s activities have largely consisted of research and development efforts related to developing electroporation delivery technologies and DNA immunotherapies and vaccines. Research and development expenses consist of expenses incurred in performing research and development activities including salaries and benefits, facilities and other overhead expenses, clinical trials, contract services and other outside expenses. Research and development expenses are charged to operations as they are incurred. These expenses result from the Company's independent research and development efforts as well as efforts associated with collaborations and licensing arrangements. The Company reviews and accrues clinical trial expense based on work performed, which relies on estimates of total costs incurred based on patient enrollment, completion of studies and other events. The Company follows this method since reasonably dependable estimates of the costs applicable to various stages of a research agreement or clinical trial can be made. Accrued clinical trial costs are subject to revisions as trials progress. Revisions are charged to expense in the period in which the facts that give rise to the revision become known. Historically, revisions have not resulted in material changes to research and development expense; however, a modification in the protocol of a clinical trial or cancellation of a trial could result in a charge to the Company's results of operations. Net Loss Per Share Basic net loss per share is computed by dividing the net loss for the year by the weighted average number of common shares outstanding during the year. Diluted net loss per share is calculated in accordance with the treasury stock method and reflects the potential dilution that would occur if securities or other contracts to issue common stock were exercised or converted to common stock. The calculation of diluted net loss per share requires that, to the extent the average market price of the underlying shares for the reporting period exceeds the exercise price of the options, warrants or other securities and the presumed exercise of such securities are dilutive to net loss per share for the period, an adjustment to net loss used in the calculation is required to remove the change in fair value of such securities from the numerator for the period. Likewise, an adjustment to the denominator is required to reflect the related dilutive shares, if any, under the treasury stock method. The following tables reconcile the components of the numerator and denominator included in the calculations of diluted net loss per share: Year Ended December 31, 2018 2017 2016 Numerator Net loss (numerator for use in basic net loss per share) $ (96,967,830 ) $ (88,205,772 ) $ (73,740,339 ) Adjustment for decrease in fair value of warrant liability — (806,819 ) — Numerator for use in diluted net loss per share $ (96,967,830 ) $ (89,012,591 ) $ (73,740,339 ) Denominator Weighted average number of common shares outstanding (denominator for use in basic net loss per share) 92,539,997 81,777,493 73,214,766 Effect of dilutive potential common shares — 140,529 — Denominator for use in diluted net loss per share 92,539,997 81,918,022 73,214,766 Net loss per share, diluted $ (1.05 ) $ (1.09 ) $ (1.01 ) Net loss per share, basic $ (1.05 ) $ (1.08 ) $ (1.01 ) The following table summarizes potential shares of common stock that were excluded from diluted net loss per share calculation because of their anti-dilutive effect: Year Ended December 31, 2018 2017 2016 Options to purchase common stock 8,752,677 7,694,870 6,806,183 Warrants to purchase common stock — — 284,091 Restricted stock units 1,688,017 1,234,168 798,834 Convertible preferred stock 8,456 8,456 8,456 Total 10,449,150 8,937,494 7,897,564 Leases Leases are classified as either capital or operating leases. Leases which transfer substantially all of the benefits and risks incidental to the ownership of assets are accounted for as if there was an acquisition of an asset and incurrence of an obligation at the inception of the lease. All other leases are accounted for as operating leases. Inovio’s Plymouth Meeting, PA headquarters and San Diego, CA facility leases, which have escalating payments, are expensed on a straight-line basis over the term of the lease. The allowance provided by the lessor for non-structural, normal leasehold improvements are considered tenant incentives and are amortized on a straight-line basis over the term of the lease. These leases represent the primary expense and commitment as indicated in Note 12, “Commitments”. Other leases exist for office machinery, such as copiers, wherein lease expense is recorded as incurred. Stock-Based Compensation The Company incurs stock-based compensation expense related to restricted stock units and stock options. The fair value of restricted stock is determined by the closing price of the Company's common stock reported on the Nasdaq Global Select Market on the date of grant. The Company estimates the fair value of stock options granted using the Black-Scholes option pricing model. The Black-Scholes option pricing model was developed for use in estimating the fair value of traded options, which have no vesting restrictions and are fully transferable. In addition, option valuation models require the input of subjective assumptions, including the expected stock price volatility and expected option life. The Company amortizes the fair value of the awards on a straight-line basis over the requisite vesting period of the awards. Expected volatility is based on historical volatility. The expected life of options granted is based on historical expected life. The risk-free interest rate is based on the U.S. Treasury yield in effect at the time of grant. The dividend yield is based on the fact that no dividends have been paid historically and none are currently expected to be paid in the foreseeable future. Upon adoption of ASU 2016-09 on January 1, 2017, the Company elected to remove the forfeiture rate from the calculation and recorded a cumulative catch-up adjustment to accumulated deficit with a corresponding offset to additional paid-in-capital of $312,000 . Previously, the forfeiture rate was based on historical data and the Company recorded stock-based compensation expense only for those awards that were expected to vest. The weighted average assumptions used in the Black-Scholes model for option grants to employees and directors are presented below: Year Ended December 31, 2018 2017 2016 Risk-free interest rate 2.73% 2.20% 0.91% Expected volatility 72% 73% 76% Expected life in years 6 6 5 Dividend yield — — — Forfeiture rate N/A N/A 7% Stock-based compensation expense related to stock options granted to non-employees is recognized based on the fair value of the stock options, determined using the Black-Scholes option pricing model, as they are earned. The fair value of the non-employee options is remeasured at each reporting period. Assumptions used in the Black-Scholes model for non-employees are presented below: Year Ended December 31, 2018 2017 2016 Risk-free interest rate 2.6%-3.0% 2.4%-2.6% 2.3%-2.5% Expected volatility 68%-101% 97%-102% 71%-104% Expected life in years 9-10 9-10 7-10 Dividend yield — — — Recent Accounting Pronouncements - Recently Adopted The recent accounting pronouncements below may have a significant effect on the Company's financial statements. Recent accounting pronouncements that are not anticipated to have an impact on or are unrelated to the Company's financial condition, results of operations, or related disclosures are not discussed. ASU No. 2014-09. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers ("Topic 606”), which amended the existing accounting standards for revenue recognition, outlines a comprehensive revenue recognition model and supersedes most current revenue recognition guidance. The new standard requires a company to recognize revenue upon transfer of goods or services to a customer at an amount that reflects the expected consideration to be received in exchange for those goods or services. The amended guidance defines a five-step approach for recognizing revenue, which will require a company to use more judgment and make more estimates than under the current guidance. The Company adopted this new standard effective January 1, 2018, using the modified retrospective transition method. The impact of adoption of Topic 606 on the Company's existing agreements was as follows: Collaboration Agreement with AstraZeneca The Company determined that no cumulative catch-up adjustment was required. Grant Agreements The Company determined that, as of January 1, 2018, accounting for the Company’s various grant agreements falls under the contributions guidance under Subtopic 958-605 , Not-for-Profit Entities-Revenue Recognition , which is outside the scope of Topic 606, as the government agencies granting the Company funds are not receiving reciprocal value for their contributions. Beginning on January 1, 2018, all contributions received from current grant agreements have been recorded as a contra-expense as opposed to revenue on the consolidated statements of operations. For the year ended December 31, 2018 , $9.5 million would have been recorded as grant revenue but under the new guidance was instead recorded as a reduction to research and development expense. The following table illustrates the impact that adopting Topic 606 has had on the Company's reported results in the consolidated statements of operations for the year ended December 31, 2018 . Balances Without Adoption of Topic 606 for the Year Ended December 31, 2018 Impact of Adopting Topic 606 As Reported for the Year Ended December 31, 2018 Revenues: Revenue under collaborative research and development arrangements $ 29,860,785 $ — $ 29,860,785 Revenue under collaborative research and development arrangements with affiliated entities 449,524 — 449,524 Grants and miscellaneous revenue 6,315,116 (6,143,528 ) 171,588 Grants and miscellaneous revenue from affiliated entity 3,348,177 (3,348,177 ) — Total revenues 39,973,602 (9,491,705 ) 30,481,897 Operating expenses: Research and development 104,749,581 (9,491,705 ) 95,257,876 General and administrative 29,315,159 — 29,315,159 Total operating expenses $ 134,064,740 $ (9,491,705 ) $ 124,573,035 ASU No. 2016-01. In January 2016, the FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities . The amended guidance requires the Company to measure and record equity investments, except those accounted for under the equity method of accounting that have a readily determinable fair value, at fair value and for the Comp

Revenue Recognition

Revenue Recognition	12 Months Ended
Revenue Recognition	Dec. 31, 2018
Revenue from Contract with Customer [Abstract]
Revenue Recognition	Revenue Recognition On January 1, 2018, the Company adopted Topic 606 using the modified retrospective method. Results for reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported in accordance with the Company’s historical accounting under Topic 605. For additional details about Topic 606, refer to Note 2 above. During the year ended December 31, 2018 , the Company recognized total revenue under collaborative research and development and other agreements of $23.0 million from ApolloBio; $6.9 million from AstraZeneca; $342,000 from its affiliated entity GeneOne; and $117,000 from various other contracts. The Company defers revenue when contract is entered into with a collaborator and cash payments are received prior to satisfaction of the related performance obligation. Of the total revenue recognized during the year ended December 31, 2018, $1.3 million was in deferred revenue as of December 31, 2017. During the twelve months ended December 31, 2017, the Company recognized revenue of $14.8 million that was included in deferred revenue at December 31, 2016. Performance obligations are generally satisfied within 12 months of the initial contract date.

Collaborative Agreements

Collaborative Agreements	12 Months Ended
Collaborative Agreements	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaborative Agreements	Collaborative Agreements ApolloBio Corporation On December 29, 2017, the Company entered into an Amended and Restated License and Collaboration Agreement (the "ApolloBio Agreement"), with ApolloBio Corporation ("ApolloBio"), with an effective date of March 20, 2018. Under the terms of the ApolloBio Agreement, the Company granted to ApolloBio the exclusive right to develop and commercialize VGX-3100, its DNA immunotherapy product designed to treat pre-cancers caused by HPV, within the territories of China, Hong Kong, Macao, Taiwan, and may include Korea in the event that no patent covering VGX-3100 is issued in China within the three years following the effective date of the ApolloBio Agreement. Under the ApolloBio Agreement, the Company received proceeds of $19.4 million in March 2018, which comprised the upfront payment of $23.0 million less $2.2 million in foreign income taxes and $1.4 million in certain foreign non-income taxes. The foreign income taxes were recorded as a provision for income taxes and the foreign non-income taxes were recorded as a general and administrative expense, on the condensed consolidated statement of operations during the quarter ended March 31, 2018. The Company also incurred advisory fees of $960,000 in connection with receiving the upfront payment from ApolloBio. These fees were determined to be incremental costs of obtaining the contract. The Company applied the practical expedient that permits a company to expense incremental costs to obtain a contract when the expected amortization period is one year or less and recorded the fees in general and administrative expense during the quarter ended March 31, 2018. No additional advisory fees are due related to the ApolloBio Agreement. In addition to the upfront payment, the Company is entitled to receive up to an aggregate of $20.0 million , less required income, withholding or other taxes, upon the achievement of specified milestones related to the regulatory approval of VGX-3100 in the United States, China and Korea. In the event that VGX-3100 is approved for marketing, the Company will be entitled to receive royalty payments based on a tiered percentage of annual net sales, with such percentage being in the low- to mid-teens, subject to reduction in the event of generic competition in a particular territory. ApolloBio’s obligation to pay royalties will continue for 10 years after the first commercial sale in a particular territory or, if later, until the expiration of the last-to-expire patent covering the licensed products in the specified territory. The Company evaluated the terms of the ApolloBio Agreement under Topic 606, and the license to VGX-3100 in the territories was identified as the only distinct performance obligation on a standalone basis as of the inception of the agreement. The Company concluded that the license was distinct from potential future manufacturing and supply obligations. The Company further determined that the transaction price under the agreement consisted of the $23.0 million upfront payment. The future potential milestone amounts were not included in the transaction price, as they were all determined to be fully constrained. As part of the evaluation of the development and regulatory milestones constraint, the Company determined that the achievement of such milestones is contingent upon success in future clinical trials and regulatory approvals, each of which is uncertain at this time. Future potential milestone amounts may be recognized as revenue under the ApolloBio Agreement, as well as under other collaborative research and development arrangements, if unconstrained. Reimbursable program costs will be recognized proportionately with the performance of the underlying services or delivery of drug supply and are excluded from the transaction price. The ApolloBio Agreement will continue in force until ApolloBio has no remaining royalty obligations. Either party may terminate the ApolloBio Agreement in the event the other party shall materially breach or default in the performance of its material obligations thereunder and such default continues for a specified period after written notice thereof. In addition, ApolloBio may terminate the ApolloBio Agreement at any time beginning one year after the effective date for any reason upon 90 days written notice to the Company. Under Topic 606, the entire transaction price of $23.0 million was allocated to the license performance obligation. The Company determined that during the quarter ended June 30, 2018, the transfer of technology occurred and accordingly, the performance obligation was fully satisfied. The Company has recorded the gross upfront payment received from ApolloBio of $23.0 million as revenue under collaborative research and development arrangements on the consolidated statement of operations during the year ended December 31, 2018. AstraZeneca On August 7, 2015, the Company entered into a license and collaboration agreement with MedImmune, the global biologics research and development arm of AstraZeneca ("AstraZeneca"). Under the agreement, AstraZeneca acquired exclusive rights to the Company's INO-3112 immunotherapy, renamed as MEDI0457, which targets cancers caused by human papillomavirus (HPV) types 16 and 18, with the ability to sublicense those license rights. AstraZeneca made an upfront payment of $27.5 million to the Company in September 2015 and agreed to make potential future development and regulatory event-based payments totaling up to $355 million and potential future commercial event-based payments totaling up to $345 million , in each case upon the achievement of specified milestones set forth in the license and collaboration agreement. AstraZeneca will fund all development costs associated with MEDI0457 immunotherapy. The Company is entitled to receive up to mid-single to double-digit tiered royalties on MEDI0457 product sales. Within the broader collaboration, at AstraZeneca’s discretion, AstraZeneca and the Company will develop up to two additional DNA-based cancer vaccine products not included in the Company's current product pipeline, which AstraZeneca will have the exclusive rights to develop and commercialize. These additional development services would be provided by the Company at an industry standard full-time-equivalent rate. Under the agreement, AstraZeneca can also request the Company to provide certain clinical manufacturing at an agreed upon price. The Company determined these options did not represent material rights at the inception of the agreement. As of December 31, 2017, the Company had recognized all of the $27.5 million upfront payment as revenue, as all identified material performance obligations had been met with respect to that payment. In December 2017 and December 2018, the Company recognized as revenue $7.0 million and $2.0 million , respectively, in milestone payments from AstraZeneca triggered by AstraZeneca’s initiation of the Phase 2 portion of ongoing clinical trials in the first and second major indication, respectively, under the agreement. During the year ended December 31, 2018 , the Company recognized total revenues of $6.9 million from AstraZeneca primarily for manufacturing services and the milestone achieved as discussed above. As of December 31, 2018 and 2017 , the Company has a deferred revenue balance of $288,000 and $1.1 million , respectively, related to AstraZeneca. The deferred revenue relates to advanced payments made by the Company to a third-party biologics manufacturer for which AstraZeneca is obligated to reimburse. As of December 31, 2018 and 2017 , the Company had an accounts receivable balance of $3.2 million and $1.7 million , respectively, related to the collaboration agreement with AstraZeneca. Prior to January 1, 2018 the Company accounted for the arrangement under Topic 605, which resulted in revenue of $22.3 million from AstraZeneca for the year ended December 31, 2017. Roche In September 2013, the Company entered into a Collaborative, License, and Option Agreement with F. Hoffmann-La Roche Ltd. and Hoffmann-La Roche Inc. (together, “Roche”) and received an upfront payment of $10.0 million . The parties agreed to co-develop multi-antigen DNA immunotherapies targeting prostate cancer and hepatitis B. On November 14, 2014, Roche provided notice to the Company that it would be partially terminating the agreement with respect to the development of the Company’s DNA immunotherapy targeting prostate cancer. The termination was effective in February 2015. All of Roche’s rights to the Company’s DNA immunotherapy targeting prostate cancer, including the right to license the product to other parties, have been returned to the Company. On July 28, 2016, Roche provided notice to the Company that it would be discontinuing the agreement and its development of INO-1800, the Company’s DNA immunotherapy against the hepatitis B virus. The termination was effective in October 2016. All of Roche’s rights to INO-1800, including the right to license the product to other parties, have been returned to the Company. In February 2017, the Company received full payment of $8.5 million from Roche for its past and future obligations which were completed during the quarter ended June 30, 2017, associated with the termination of the agreement. During the year ended December 31, 2018 , the Company recognized no revenues from Roche. During the year ended December 31, 2017 , the Company recognized revenues of $6.1 million from Roche. Coalition for Epidemic Preparedness Innovations On April 11, 2018, the Company entered into agreements with the Coalition for Epidemic Preparedness Innovations ("CEPI"), pursuant to which the Company intends to develop vaccine candidates against Lassa fever and MERS. The goal of the collaboration between the Company and CEPI is to conduct research and development so that investigational stockpiles will be ready for clinical efficacy trial testing during potential disease outbreaks. The agreements with CEPI contemplate preclinical studies, as well as Phase 1 and Phase 2 clinical trials, occurring over the next few years. As part of the arrangement between the parties, CEPI has agreed to fund up to an aggregate of $56 million of costs over a five -year period for preclinical studies, as well as planned Phase 1 and Phase 2 clinical trials, to be conducted by the Company and collaborators, with funding from CEPI based on the achievement of identified milestones. During the year ended December 31, 2018 , the Company received upfront funding of $6.5 million related to the CEPI grant, and recorded $4.3 million as contra-research and development expense. As of December 31, 2018 , the Company had a deferred grant funding balance related to the CEPI grant of $2.1 million recorded as deferred grant funding on the consolidated balance sheet. DARPA- Ebola In April 2015, the Company received a grant from the Defense Advanced Research Projects Agency ("DARPA") to lead a collaborative team to develop multiple treatment and prevention approaches against Ebola. The consortium, led by the Company, is taking a multi-faceted approach to develop products to prevent and treat Ebola infection. The award covers pre-clinical development costs as well as good manufacturing practice, manufacturing costs and the Phase 1 clinical study costs. The initial funding period covers a base award of $19.6 million and an option award of $24.6 million , which was exercised in September 2015. During the year ended December 31, 2018 , the Company received funding of $1.1 million related to the DARPA Ebola grant and recorded it as contra-research and development expense. During the year ended December 31, 2017, the Company recognized revenues of $9.8 million related to the DARPA Ebola grant. As of December 31, 2018 the Company had a deferred grant funding balance of $74,000 , and as of December 31, 2017 the Company had a deferred revenue balance of $149,000 , related to the DARPA grant. As of December 31, 2018 and 2017 , the Company had an accounts receivable balance of $82,000 and $4.1 million, respectively, related to the DARPA grant.

Investments

Investments	12 Months Ended
Investments	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Investments	Investments Investments at December 31, 2018 consisted of mutual funds and United States corporate debt securities. Investments at December 31, 2017 consisted of mutual funds, United States corporate debt securities and an equity investment in the Company's affiliated entity PLS. Investments are recorded at fair value, based on current market valuations. After the adoption of ASU No. 2016-01 on January 1, 2018, unrealized gains and losses on the Company's equity securities are reported in the consolidated statement of operations as non-operating other income (expense). Unrealized gains and losses on the Company's debt securities will continue to be excluded from earnings and are reported as a separate component of other comprehensive loss until realized. Realized gains and losses are included in non-operating other income (expense) on the consolidated statement of operations and are derived using the specific identification method for determining the cost of the securities sold. During the years ended December 31, 2018 and 2017 , net realized loss on investments of $1.3 million and $215,000 , respectively, was recorded. The Company assessed each of its investments on an individual basis to determine if any decline in fair value was other-than-temporary. Interest and dividends on investments classified as available-for-sale are included in interest and other income, net, in the consolidated statements of operations. There were no impairments considered to be other-than-temporary during the years ended December 31, 2018 and 2017 . As of December 31, 2018 , the Company had 14 available-for-sale securities in a gross unrealized loss position, of which 10 with an aggregate total unrealized loss of $193,000 were in such position for longer than 12 months. The following is a summary of available-for-sale securities as of December 31, 2018 and 2017 : As of December 31, 2018 Contractual Maturity (in years) Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value Mutual funds --- $ 57,842,955 $ — $ (528,084 ) $ 57,314,871 US corporate debt securities Less than 2 224,633 — (652 ) 223,981 Total investments $ 58,067,588 $ — $ (528,736 ) $ 57,538,852 As of December 31, 2017 Contractual Maturity (in years) Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value Mutual funds --- $ 68,776,165 $ 42,097 $ (252,373 ) $ 68,565,889 US corporate debt securities Less than 2 35,210,121 3,032 (140,198 ) 35,072,955 Investment in affiliated entity (PLS) --- — 2,325,079 — 2,325,079 Total investments $ 103,986,286 $ 2,370,208 $ (392,571 ) $ 105,963,923

Marketable Securities and Fair

Marketable Securities and Fair Value Measurements	12 Months Ended
Marketable Securities and Fair Value Measurements	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Marketable Securities and Fair Value Measurements	Marketable Securities and Fair Value Measurements The guidance regarding fair value measurements establishes a three-tier fair value hierarchy which prioritizes the inputs used in measuring fair value. These tiers include: Level 1, defined as observable inputs such as quoted prices in active markets that are accessible at the measurement date; Level 2, defined as inputs other than quoted prices in active markets that are either directly or indirectly observable; and Level 3, defined as unobservable inputs in which little or no market data exists, therefore requiring an entity to develop its own assumptions. Assets and liabilities are classified based on the lowest level of input that is significant to the fair value measurements. The Company reviews the fair value hierarchy classification on a quarterly basis. Changes in the ability to observe valuation inputs may result in a reclassification of levels for certain securities within the fair value hierarchy. The Company did not have any transfer of assets and liabilities between Level 1, Level 2 and Level 3 of the fair value hierarchy during the years ended December 31, 2018 and 2017 . The following table presents the Company’s assets that are measured at fair value on a recurring basis, and are determined using the following inputs as of December 31, 2018 : Fair Value Measurements at December 31, 2018 Total Quoted Prices in Active Markets (Level 1) Significant Other Unobservable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds $ 9,646,507 $ 9,646,507 $ — $ — Mutual funds 57,314,871 — 57,314,871 — US corporate debt securities 223,981 — 223,981 — Investments in affiliated entities 9,405,913 9,405,913 — — Total assets $ 76,591,272 $ 19,052,420 $ 57,538,852 $ — The following table presents the Company’s assets and liabilities that are measured at fair value on a recurring basis, and are determined using the following inputs as of December 31, 2017 : Fair Value Measurements at December 31, 2017 Total Quoted Prices in Active Markets (Level 1) Significant Other Unobservable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds $ 9,843,482 $ 9,843,482 $ — $ — Mutual funds 68,565,889 — 68,565,889 — US corporate debt securities 35,072,955 — 35,072,955 — Investments in affiliated entities 11,394,480 11,394,480 — — Total assets $ 124,876,806 $ 21,237,962 $ 103,638,844 $ — Liabilities: Common stock warrants $ 360,795 $ — $ — $ 360,795 Total liabilities $ 360,795 $ — $ — $ 360,795 Level 1 assets at December 31, 2018 and 2017 consisted of money market funds held by the Company that are valued at quoted market prices, as well as the Company’s investments in affiliates, GeneOne and PLS. The Company accounts for its investment in 1,644,155 common shares of GeneOne based on the closing price of the shares on the Korean Stock Exchange on the applicable balance sheet date. The Company accounts for its investment in 395,758 common shares of PLS as an equity investment with a fair value based on the closing price of the shares on the Korea New Exchange (KONEX) Market on the applicable balance sheet date. The Company elected the fair value option in conjunction with the investment in GeneOne at the inception of the investment; therefore, changes in the fair value of the investment are reflected as other income (expense) in the consolidated statements of operations. The Company did not elect the fair value option for the investment in PLS at the inception of the investment, but rather recorded the investment under the equity method until its ownership interest dropped below 20% in June 2015 and, accordingly, began recording the investment under the cost method using the carryover basis from the equity method of zero . Once shares of PLS began trading on the KONEX, the Company classified the investment as available-for-sale and began recording the investment at fair value. After the adoption of ASU No. 2016-01 on January 1, 2018, unrealized gains and losses on the Company's equity securities are reported in the consolidated statement of operations as a gain (loss) on investment in affiliated entities, as discussed in Note 2. Level 2 assets at December 31, 2018 and 2017 consisted of U.S. corporate debt securities and mutual funds held by the Company that are initially valued at the transaction price and subsequently valued, at the end of each reporting period, typically utilizing market observable data. The Company obtains the fair value of its Level 2 assets from a professional pricing service, which may use quoted market prices for identical or comparable instruments, or inputs other than quoted prices that are observable either directly or indirectly. The professional pricing service gathers quoted market prices and observable inputs from a variety of industry data providers. The valuation techniques used to measure the fair value of the Company's Level 2 financial instruments were derived from non-binding market consensus prices that are corroborated by observable market data, quoted market prices for similar instruments, or pricing models such as discounted cash flow techniques. The Company validates the quoted market prices provided by the primary pricing service by comparing the service's assessment of the fair values of the Company's investment portfolio balance against the fair values of the Company's investment portfolio balance obtained from an independent source. There were no Level 3 assets held as of December 31, 2018 and 2017 . There were no Level 3 liabilities held as of December 31, 2018 . Level 3 liabilities as of December 31, 2017 consisted of common stock warrant liabilities associated with warrants to purchase the Company's common stock issued in March 2013. During the third quarter of 2018 , all of the remaining 284,091 warrants were exercised for net proceeds to the Company of $902,000 . During the year ended December 31, 2017 , none of these warrants were exercised. As of December 31, 2017, the Company had a $361,000 common stock warrant liability. The Company reassessed the fair value of the common stock warrants at each reporting date utilizing a Black-Scholes pricing model. Inputs used in the pricing model include estimates of stock price volatility, expected warrant life and risk-free interest rate. The Company develops its estimates based on historical data. The assumptions used to estimate the fair value of common stock warrants at December 31, 2017 is presented below: Year Ended December 31, 2017 Risk-free interest rate 1.75% Expected volatility 55% Expected life in years 0.70 Dividend yield — Changes in these assumptions as well as fluctuations in the Company's stock price between the valuation dates can have a significant impact on the fair value of the common stock warrant liability. As a result of these calculations, the Company recorded a decrease in fair value of $(361,000) , $(807,000) and $(134,000) for the years ended December 31, 2018 , 2017 and 2016 , respectively. The change in fair value is reflected in the Company's consolidated statement of operations as a component of change in fair value of common stock warrants. The following table presents the changes in fair value of the Company’s total Level 3 financial liabilities for the years ended December 31, 2018 and 2017 : Year Ended December 31, 2018 2017 Balance at beginning of year $ 360,795 $ 1,167,614 Decrease in fair value included in change in fair value of common stock warrants (360,795 ) (806,819 ) Balance at end of year $ — $ 360,795

Major Customers and Concentrati

Major Customers and Concentration of Credit Risk	12 Months Ended
Major Customers and Concentration of Credit Risk	Dec. 31, 2018
Risks and Uncertainties [Abstract]
Major Customers and Concentration of Credit Risk	Major Customers and Concentration of Credit Risk Customer 2018 Revenue % of Total Revenue 2017 Revenue % of Total Revenue 2016 Revenue % of Total Revenue ApolloBio $ 23,000,000 75 % $ — — % $ — — % AstraZeneca 6,850,424 23 22,269,773 53 1,518,639 4 DARPA — — 9,983,927 24 26,602,183 75 Roche — — 6,107,254 14 4,917,929 14 GeneOne (affiliated entity) 342,386 1 551,208 1 1,188,432 4 All other 289,087 1 3,307,924 8 1,141,178 3 Total revenue $ 30,481,897 100 % $ 42,220,086 100 % $ 35,368,361 100 % During the year ended December 31, 2018 , the Company recognized revenue from various license fees and collaborative research and development agreements. The Company has determined that as of January 1, 2018, accounting for the Company’s various grant agreements falls under the contributions guidance under Subtopic 958-605 , Not-for-Profit Entities-Revenue Recognition , which is outside the scope of Topic 606. Beginning on January 1, 2018, all contributions received from current grant agreements have been recorded as a contra-expense as opposed to revenue on the consolidated statements of operations, as discussed in Note 2. During the years ended December 31, 2017 and 2016 , the Company recognized revenue from various license fees, collaborative research and development agreements, grants and government contracts. As of December 31, 2018 , $3.2 million , or 98% , of the Company's accounts receivable was attributable to AstraZeneca. As of December 31, 2017 , $4.1 million , or 69% , and $ 1.7 million , or 28% , of the Company's accounts receivable was attributable to DARPA and AstraZeneca, respectively. There is minimal credit risk with these customers based upon collection history, their size and financial condition. Accordingly, the Company does not consider it necessary to record a reserve for uncollectible accounts receivable.

Fixed Assets

Fixed Assets	12 Months Ended
Fixed Assets	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Fixed Assets	Fixed Assets Fixed assets at December 31, 2018 and 2017 consist of the following: Cost Accumulated Depreciation and Amortization Net Book Value As of December 31, 2018 Leasehold improvements $ 14,909,341 $ (3,464,444 ) $ 11,444,897 Laboratory equipment 4,031,965 (2,425,854 ) 1,606,111 Office furniture and fixtures 3,198,803 (1,767,653 ) 1,431,150 Computer equipment and other 3,808,824 (2,341,968 ) 1,466,856 $ 25,948,933 $ (9,999,919 ) $ 15,949,014 As of December 31, 2017 Leasehold improvements $ 14,553,993 $ (2,042,871 ) $ 12,511,122 Laboratory equipment 3,787,578 (1,724,946 ) 2,062,632 Office furniture and fixtures 3,366,896 (1,471,705 ) 1,895,191 Computer equipment and other 3,718,266 (1,867,035 ) 1,851,231 $ 25,426,733 $ (7,106,557 ) $ 18,320,176 Depreciation expense for the years ended December 31, 2018 , 2017 and 2016 was $3.7 million , $1.9 million and $1.7 million , respectively. The Company determined that the carrying value of these long-lived assets was not impaired during the periods presented.

Goodwill and Intangible Assets

Goodwill and Intangible Assets	12 Months Ended
Goodwill and Intangible Assets	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets The following sets forth goodwill and intangible assets by major asset class: December 31, 2018 December 31, 2017 Useful Life (Yrs) Gross Accumulated Amortization Net Book Value Gross Accumulated Amortization Net Book Value Indefinite lived: Goodwill(a) $ 10,513,371 $ — $ 10,513,371 $ 10,513,371 $ — $ 10,513,371 Definite lived: Patents 8 – 17 5,802,528 (5,742,079 ) 60,449 5,802,528 (5,681,673 ) 120,855 Licenses 8 – 17 1,323,761 (1,219,357 ) 104,404 1,323,761 (1,190,609 ) 133,152 CELLECTRA ® (b) 5 – 11 8,106,270 (7,679,190 ) 427,080 8,106,270 (7,252,108 ) 854,162 GHRH(b) 11 335,314 (303,630 ) 31,684 335,314 (271,948 ) 63,366 Bioject (c) 2 – 15 5,100,000 (1,882,222 ) 3,217,778 5,100,000 (1,405,556 ) 3,694,444 Other(d) 18 4,050,000 (3,131,250 ) 918,750 4,050,000 (2,906,250 ) 1,143,750 Total intangible assets 24,717,873 (19,957,728 ) 4,760,145 24,717,873 (18,708,144 ) 6,009,729 Total goodwill and intangible assets $ 35,231,244 $ (19,957,728 ) $ 15,273,516 $ 35,231,244 $ (18,708,144 ) $ 16,523,100 (a) Goodwill was recorded from the Inovio AS acquisition in January 2005, the acquisition of VGX in June 2009 and the acquisition of Bioject in April 2016 for $3.9 million , $6.2 million and $400,000 , respectively. (b) CELLECTRA ® and GHRH are developed technologies which were recorded from the acquisition of VGX. (c) Bioject intangible assets represent the estimated fair value of developed technology and intellectual property which were recorded from the Bioject asset acquisition. (d) Other intangible assets represent the estimated fair value of acquired intellectual property from the Inovio AS acquisition. Aggregate amortization expense on intangible assets was $1.2 million , $1.6 million and $1.4 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. Amortization expense related to intangible assets at December 31, 2018 is expected to be incurred as follows: Year ending December 31, 2019 $ 1,066,251 2020 547,081 2021 520,414 2022 492,818 2023 275,803 Thereafter 1,857,778 $ 4,760,145 There were no impairment or impairment indicators present and no losses were recorded during the years ended December 31, 2018 , 2017 and 2016 , respectively.

Accounts Payable and Accrued Ex

Accounts Payable and Accrued Expenses	12 Months Ended
Accounts Payable and Accrued Expenses	Dec. 31, 2018
Payables and Accruals [Abstract]
Accounts Payable and Accrued Expenses	Accounts Payable and Accrued Expenses Accounts payable and accrued expenses at December 31, 2018 and 2017 consist of the following: As of December 31, 2018 2017 Trade accounts payable $ 10,043,816 $ 7,564,830 Accrued compensation 9,466,821 7,997,152 Accrued subcontract costs 83,812 3,746,937 Other accrued expenses 3,540,284 3,969,879 $ 23,134,733 $ 23,278,798

Stockholders' Equity

Stockholders' Equity	12 Months Ended
Stockholders' Equity	Dec. 31, 2018
Stockholders' Equity Note [Abstract]
Stockholders' Equity	Stockholders’ Equity Preferred Stock Shares Outstanding as of December 31, Shares Authorized Shares Issued 2018 2017 Series C Preferred Stock, par $0.001 1,091 1,091 23 23 The shares of the Company’s Series C Preferred Stock have the following pertinent rights and privileges, as set forth in the Company’s Amended and Restated Certificate of Incorporation and its Certificates of Designations, Rights and Preferences related to the various series of preferred stock. Rights on Liquidation In the event of any voluntary or involuntary liquidation, dissolution or winding up of the Company (a “liquidation event”), before any distribution of assets of the Company shall be made to or set apart for the holders of common stock, the holders of Series C Preferred Stock, pari passu, are entitled to receive payment of such assets of the Company in an amount equal to $10,000 per share of such series of preferred stock, plus any accumulated and unpaid dividends thereon (whether or not earned or declared). If the assets of the Company available for distribution to stockholders exceed the aggregate amount of the liquidation preferences payable with respect to all shares of each series of preferred stock then outstanding, then, after the payment of such preferences is made or irrevocably set aside, the holders of the Company’s common stock are entitled to receive a pro rata portion of such assets based on the aggregate number of shares of common stock held by each such holder. The holders of the Company’s outstanding preferred stock shall participate in such a distribution on a pro-rata basis, computed based on the number of shares of common stock which would be held by such preferred holders if immediately prior to the liquidation event all of the outstanding shares of the preferred stock had been converted into shares of common stock at the then current conversion value applicable to each series. A Change of Control of the Company (as defined in the Certificates of Designations, Rights and Preferences) is not a liquidation event triggering the preferences described above, and is instead addressed by separate terms in the Series C Certificates of Designations, Rights, and Preferences. Although the liquidation preferences are in excess of the par value of $0.001 per share of the Company’s preferred stock, these preferences are equal to or less than the stated value of such shares based on their original purchase price. Voting Rights The holders of Series C Preferred Stock have full voting rights and powers equal to the voting rights and powers of holders of the Company’s common stock and are entitled to notice of any stockholders’ meeting in accordance with the Company’s Bylaws. Holders are entitled to vote on any matter upon which holders of the Company’s common stock have the right to vote, including, without limitation, the right to vote for the election of directors together with the holders of common stock as one class. Series C Preferred holders are entitled to 368 votes for each share of Series C Preferred Stock held. Holder Optional Conversion Right The holder of any share or shares of Series C Preferred Stock has the right at any time, at such holder’s option, to convert all or any lesser portion of such holder’s shares of the Preferred Stock into such number of fully paid and non-assessable shares of Common Stock as is determined by dividing (i) the aggregate Liquidation Preference applicable to the particular series of preferred shares, plus accrued and unpaid dividends thereon by (ii) the applicable Conversion Value (as defined in the relevant series’ Certificate of Designations, Rights and Preferences) then in effect for such series of preferred shares. As of December 31, 2018, the Conversion Value was $27.20 , such that the outstanding shares of Series C Preferred Stock were convertible into 8,456 shares of common stock. The Company is not obligated to issue any fractional shares or scrip representing fractional shares upon such conversion and instead shall pay the holder an amount in cash equal to such fraction multiplied by the current market price per share of the Company’s common stock. Company Mandatory Conversion Option The Company has the option upon thirty (30) days prior written notice, to convert all of the outstanding shares of the Series C Preferred Stock into such number of fully paid and non-assessable shares of common stock as is determined by dividing (i) the aggregate Liquidation Preference of the shares of the relevant series of preferred stock to be converted, plus accrued and unpaid dividends thereon by (ii) the applicable Conversion Value (as defined in the relevant series’ Certificate of Designations, Rights and Preferences) then in effect, if the following triggering events have occurred: (i) the price of the Company’s common stock exceeds $72.00 per share for 20 out of 30 consecutive trading days; and (ii) the average daily trading volume (subject to adjustment for stock dividends, subdivisions and combinations) of the common stock exceeds 6,250 shares for at least 20 out of 30 consecutive trading days. Common Stock In May 2018, the Company entered into an At-the-Market Equity Offering Sales Agreement (the “Sales Agreement”) with an outside placement agent (the “Placement Agent”) to sell shares of its common stock with aggregate gross proceeds of up to $100.0 million , from time to time, through an “at-the-market” equity offering program under which the Placement Agent will act as sales agent. Under the Sales Agreement, the Company will set the parameters for the sale of shares, including the number of shares to be issued, the time period during which sales are requested to be made, limitation on the number of shares that may be sold in any one trading day and any minimum price below which sales may not be made. The Sales Agreement provides that the Placement Agent will be entitled to compensation for its services in an amount equal to up to 3.0% of the gross proceeds from the sales of shares sold through the Placement Agent under the Sales Agreement. The Company has no obligation to sell any shares under the Sales Agreement, and may at any time suspend solicitation and offers under the Sales Agreement. During the year ended December 31, 2018 , the Company sold a total of 5,354,075 shares of common stock under the Sales Agreement. The sales were made at a weighted average price of $5.27 per share resulting in aggregate net proceeds of $27.7 million . The Company may sell up to an additional $71.8 million in shares of its common stock under the Sales Agreement. The registration statement that registered with the SEC the shares that may be sold under the Sales Agreement expires on June 8, 2021. In June 2016, the Company entered into an At-the-Market Equity Offering Sales Agreement (the “Prior Sales Agreement”) with the same placement agent. The registration statement that registered with the SEC the shares sold under the Prior Sales Agreement expired on June 5, 2018, and no further sales will be made under the Prior Sales Agreement. The Company sold an aggregate of 3,911,104 shares of common stock under the Prior Sales Agreement resulting in aggregate net proceeds of $32.1 million . During the period beginning January 1 and ending June 5, 2018, the Company sold a total of 314,950 shares of common stock under the Prior Sales Agreement. The sales were made at a weighted average price of $5.07 per share resulting in aggregate net proceeds of $1.6 million . During the year ended December 31, 2017, the Company sold a total of 2,937,406 shares of common stock under the Prior Sales Agreement. The sales were made at a weighted average price of $8.41 per share resulting in aggregate net proceeds of $24.2 million . On July 25, 2017, the Company closed an underwritten public offering of 12,500,000 shares of common stock at a public offering price of $6.00 per share. The net proceeds to the Company, after deducting the underwriters' discounts and commissions and other offering expenses, were $70.1 million. Warrants During the year ended December 31, 2018, warrants to purchase 284,091 shares of the Company's common stock were exercised, with net proceeds to the Company of $902,000 . No common stock warrants were exercised during the year ended December 31, 2017. As of December 31, 2018 there were no common stock warrants outstanding. Previously, the Company accounted for the common stock warrants issued in March 2013 under the authoritative guidance on accounting for derivative financial instruments indexed to, and potentially settled in, a company’s own stock, on the understanding that in compliance with applicable securities laws, the registered warrants required the issuance of registered securities upon exercise and did not sufficiently preclude an implied right to net cash settlement. The Company classified registered warrants on the consolidated balance sheet as a current liability which was revalued at each balance sheet date subsequent to the initial issuance. Changes in the fair market value of the warrants were reflected in the consolidated statement of operations as change in fair value of common stock warrants. The following table summarizes the warrants outstanding as of December 31, 2018 and 2017 : As of December 31, 2018 As of December 31, 2017 Issued in Connection With: Exercise Price Expiration Date Number of Warrants Common Stock Warrant Liability Number of Warrants Common Stock Warrant Liability March 2013 financing $ 3.17 September 12, 2018 — $ — 284,091 $ 360,795 Total — $ — 284,091 $ 360,795 Stock Options and Restricted Stock Units The Company has a stock-based incentive plan, the 2016 Omnibus Incentive Plan (the "2016 Incentive Plan"), pursuant to which the Company may grant stock options, restricted stock awards, restricted stock units and other stock-based awards or short-term cash incentive awards to employees, directors and consultants. The 2016 Incentive Plan was approved by the Company's stockholders on May 13, 2016. The maximum number of shares of the Company’s common stock available for issuance over the term of the 2016 Incentive Plan may not exceed 6,000,000 shares, provided that commencing with the first business day of each calendar year beginning January 1, 2018, such maximum number of shares shall be increased by 2,000,000 shares of common stock unless the Board determines, prior to January 1 for any such calendar year, to increase such maximum amount by a fewer number of shares or not to increase the maximum amount at all for such year. On January 1, 2018, the maximum number of shares to be issued was increased by 2,000,000 . At December 31, 2018 , there were 8,000,000 shares of common stock reserved for issuance upon exercise of incentive awards granted and to be granted at future dates under the 2016 Incentive Plan. At December 31, 2018 , the Company had 3,039,566 shares of common stock available for future grant under the 2016 Incentive Plan, 1,519,187 shares underlying outstanding but unvested restricted stock units and options outstanding to purchase 3,062,183 shares of common stock under the 2016 Incentive Plan. The awards granted and available for future grant under the 2016 Incentive Plan generally vest over three years and have a maximum contractual term of ten years. The 2016 Incentive Plan terminates by its terms on March 9, 2026. The Amended and Restated 2007 Omnibus Incentive Plan (the "2007 Incentive Plan") was adopted on March 31, 2007 and terminated by its terms on March 31, 2017. At December 31, 2018 , the Company had 168,830 shares underlying outstanding but unvested restricted stock units and options outstanding to purchase 5,690,494 shares of common stock under the 2007 Incentive Plan. The awards granted under the 2007 Incentive Plan generally vest over three years and have a maximum contractual term of ten years. Total employee and director stock-based compensation expense recognized in the consolidated statement of operations for the years ended December 31, 2018 , 2017 and 2016 was $10.2 million , $12.9 million and $10.2 million , respectively, of which $5.9 million , $5.8 million and $4.8 million was included in research and development expenses and $4.3 million , $7.1 million and $5.4 million was included in general and administrative expenses, respectively. At December 31, 2018 and 2017 , there was $5.2 million and $5.9 million , respectively, of total unrecognized compensation expense related to unvested stock options, which is expected to be recognized over a weighted-average period of 1.7 years and 1.8 years, respectively. At December 31, 2018 and 2017 , there was $5.1 million and $5.3 million , respectively, of total unrecognized compensation expense related to unvested restricted stock units, which is expected to be recognized over a weighted-average period of 1.7 years and 1.8 years, respectively. The fair value of stock options granted to non-employees at the measurement dates were estimated using the Black-Scholes pricing model. Total stock-based compensation expense for stock options and restricted stock units granted to non-employees for the years ended December 31, 2018 , 2017 and 2016 was $302,000 , $201,000 and $321,000 , respectively. As of December 31, 2018 , options to purchase 628,125 shares of common stock granted to non-employees remained outstanding. The following table summarizes total stock options outstanding at December 31, 2018 : Options Outstanding Options Exercisable Exercise Price Shares Underlying Options Outstanding Weighted-Average Remaining Contractual Life (in Years) Weighted Average Exercise Price Shares Underlying Options Exercisable Weighted Average Exercise Price $1.48-$3.00 879,321 3.7 $ 2.26 879,321 $ 2.26 $3.01-$6.00 2,558,453 7.9 $ 4.38 974,723 $ 4.44 $6.01-$9.00 4,394,357 6.7 $ 7.11 3,408,953 $ 7.20 $9.01-$12.00 257,836 6.9 $ 9.79 228,788 $ 9.81 $12.01-$15.00 662,710 5.2 $ 12.96 662,710 $ 12.96 8,752,677 6.7 $ 6.35 6,154,495 $ 6.78 At December 31, 2018 , the aggregate intrinsic value of options outstanding was $1.6 million , the aggregate intrinsic value of options exercisable was $1.6 million , and the weighted average remaining contractual term of options exercisable was 5.8 years. At December 31, 2018 , the aggregate intrinsic value of unvested restricted stock units was $6.8 million and the aggregate intrinsic value of restricted stock units which vested during the year ended December 31, 2018 was $2.4 million. At December 31, 2018 , options to purchase 8,752,677 shares of common stock and 1,688,017 restricted stock units were expected to vest. Stock option activity under the Company’s equity incentive plans during the year ended December 31, 2018 was as follows: Number of Shares Weighted-Average Exercise Price Balance, December 31, 2017 7,694,870 $ 6.77 Granted 2,176,935 4.32 Exercised (472,762 ) 3.21 Cancelled (646,366 ) 6.83 Balance, December 31, 2018 8,752,677 $ 6.35 Restricted stock unit activity under the Company’s equity incentive plans during the year ended December 31, 2018 was as follows: Number of Shares Weighted-Average Exercise Price Balance, December 31, 2017 1,234,168 $ — Granted 1,070,106 — Vested (539,468 ) — Cancelled (76,789 ) — Balance, December 31, 2018 1,688,017 $ — The weighted average exercise price per share was $5.17 for the 119,091 options which expired during the year ended December 31, 2018 , $9.67 for the 200,501 options which expired during the year ended December 31, 2017 and $9.01 for the 69,570 options which expired during the year ended December 31, 2016 . The weighted average grant date fair value per share was $2.86 , $4.33 and $4.59 for options granted during the years ended December 31, 2018 , 2017 and 2016 , respectively. The weighted average grant date fair value was $4.31 , $6.66 and $7.41 per share for restricted stock units granted during the years ended December 31, 2018 , 2017 and 2016 , respectively. The Company received $1.5 million , $2.3 million and $1.8 million in proceeds from the exercise of stock options during the years ended December 31, 2018 , 2017 and 2016 , respectively. The aggregate intrinsic value of options exercised was $910,000 , $519,000 and $3.5 million during the years ended December 31, 2018 , 2017 and 2016 , respectively.

Commitments

Commitments	12 Months Ended
Commitments	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments	Commitments San Diego Leases In April 2013, the Company entered into a lease for 26,500 square feet of office space located in San Diego, California (the "San Diego Lease"). The term of the San Diego Lease commenced on December 1, 2013. The initial term of the San Diego Lease is ten years, with a right to terminate on December 1, 2019 and a right to extend the term by five years, subject to specified conditions. In June 2015, the Company amended the San Diego Lease to increase the total leased space to 31,207 square feet and occupy the entire building. The commencement of the amended San Diego Lease was in January 2016. As of December 31, 2018, rent payments under the San Diego Lease include base rent with an annual increase of approximately 3 percent , and additional monthly fees to cover the Company’s share of certain facility expenses, including utilities, property taxes, insurance and maintenance. The Company has capitalized $3.4 million of total tenant improvements within fixed assets on the consolidated balance sheet related to the entire building and has recorded a corresponding increase to deferred rent. In October 2016, the Company entered into an office lease (the “new Lease”) for a second property located in San Diego, California. The total space under the new Lease is approximately 51,000 square feet. The Company is using the facility for office, manufacturing and research and development purposes. The term of the new Lease commenced on June 1, 2017. The initial term of the new Lease is ten years, with a right to terminate on November 30, 2023, subject to specified conditions. The base rent adjusts periodically throughout the term of the new Lease. As of December 31, 2018, rent payments under the San Diego Lease include base rent with an annual increase of approximately 3 percent , and additional monthly fees to cover the Company’s share of certain facility expenses, including utilities, property taxes, insurance and maintenance. In addition, the Company has paid a security deposit of $95,000 . The Company has capitalized $2.3 million of reimbursable tenant improvements to the new office which has been recorded as a leasehold improvement within fixed assets on the consolidated balance sheet, offset by a corresponding amount recorded in deferred rent. Plymouth Meeting Lease In March 2014, the Company entered into a lease (the "Lease") for 20,858 square feet of office space located in Plymouth Meeting, Pennsylvania. The Company occupied the space in June 2014. The initial term of the Lease was 11.5 years, with a right to extend the term by five years, subject to specified conditions. The base rent adjusts periodically throughout the term of the Lease. As of December 31, 2018, rent payments under the Lease include base rent with an annual increase of approximately 2 percent , and additional monthly fees to cover the Company’s share of certain facility expenses, including utilities, property taxes, insurance and maintenance. In addition, the Company has paid a security deposit of $49,000 . In July 2015, the Company amended the Lease to increase the total leased space to 27,583 square feet. The Company has capitalized $2.6 million of tenant improvements to the Plymouth Meeting office within fixed assets on the consolidated balance sheet, offset by a corresponding amount recorded in deferred rent. In June 2017, the Company entered into another amendment to the Lease to increase the total leased space to 57,361 square feet and extend the lease term through December 31, 2029. In connection with this amendment, the Company has paid the landlord an additional security deposit of $75,000 . Rent expense was $3.2 million , $2.4 million and $1.6 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. The terms of the leases provide for rental payments on a monthly basis on a graduated scale. The Company recognizes rent expense on a straight-line basis over the lease period. Future minimum lease payments under non-cancelable operating leases as of December 31, 2018 are as follows: Year ending December 31, 2019 $ 3,756,000 2020 3,891,000 2021 3,979,000 2022 4,052,000 2023 4,023,000 Thereafter 15,952,000 Total $ 35,653,000 In the normal course of business, the Company is a party to a variety of agreements pursuant to which it may be obligated to indemnify the other party. It is not possible to predict the maximum potential amount of future payments under these types of agreements due to the conditional nature of the Company's obligations and the unique facts and circumstances involved in each particular agreement. Historically, payments made by us under these types of agreements have not had a material effect on the Company's business, consolidated results of operations or financial condition.

Investments in Affiliated Entit

Investments in Affiliated Entities	12 Months Ended
Investments in Affiliated Entities	Dec. 31, 2018
Related Party Transactions [Abstract]
Investments in Affiliated Entities	Investments in Affiliated Entities The Company held 1,644,155 common shares, representing a 7.8% ownership interest in GeneOne as of December 31, 2018 and 2017 , and 395,758 common shares, representing a 15.1% and 16.4% ownership interest in PLS as of December 31, 2018 and 2017 , respectively. Please see further information as discussed in Note 2 and Note 6.

Income Taxes

Income Taxes	12 Months Ended
Income Taxes	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes In accordance with the guidance pursuant to accounting for income taxes, a deferred tax asset or liability is determined based on the difference between the financial statement and tax basis of assets and liabilities as measured by the enacted tax rates which will be in effect when these differences reverse. The Company provides a valuation allowance against net deferred tax assets unless, based upon the available evidence, it is more likely than not that the deferred tax asset will be realized. The components of the provision for income taxes are presented in the following table: Year Ended December 31, 2018 2017 2016 Current: Federal $ — $ — $ — State — — — Foreign 2,170,000 — — 2,170,000 — — Deferred: Federal — — State — — — Foreign — — — — — — $ 2,170,000 $ — $ — The reconciliation of income taxes attributable to continuing operations computed at the statutory tax rates to income tax expense (recovery), using a 21% statutory tax rate for December 31, 2018, and 35% statutory tax rate for December 31, 2017 and 2016, is as follows: Year Ended December 31, 2018 2017 2016 Income (benefit) taxes at statutory rates $ (19,908,000 ) $ (30,872,000 ) $ (25,809,000 ) State income tax, net of federal benefit (4,000 ) (4,000 ) (4,000 ) Foreign income taxes 2,170,000 — — Change in valuation allowance 20,898,000 (20,965,000 ) 29,678,000 Research and development tax credits (3,170,000 ) (3,456,000 ) (3,117,000 ) Fair value warrant (76,000 ) (282,000 ) (47,000 ) Stock compensation 1,094,000 2,332,000 113,000 Uncertain tax positions 1,268,000 846,000 1,367,000 Expired NOLs and credits 2,176,000 454,000 4,269,000 Limited NOLs and credits (2,176,000 ) (165,000 ) (6,456,000 ) Change in tax rates — 50,019,000 (495,000 ) Other (102,000 ) 2,093,000 501,000 $ 2,170,000 $ — $ — The income tax expense recorded during the year ended December 31, 2018 of $2.2 million was related to foreign income taxes on the upfront payment received from ApolloBio in March 2018. Significant components of the Company’s deferred tax assets and liabilities as of December 31, 2018 and 2017 are shown below: As of December 31, 2018 2017 Deferred tax assets: Capitalized research expense $ 7,408,000 $ 8,546,000 Net operating loss carryforwards 89,399,000 71,665,000 Research and development and other tax credits 9,432,000 7,531,000 Deferred revenue 985,000 297,000 Deferred rent 2,013,000 2,097,000 Stock-based compensation 3,408,000 3,091,000 Acquired intangibles 912,000 858,000 Other 2,693,000 1,906,000 116,250,000 95,991,000 Valuation allowance (115,007,000 ) (94,039,000 ) Total deferred tax assets 1,243,000 1,952,000 Deferred tax liabilities: Acquired intangibles (142,000 ) (124,000 ) Investment in affiliated entity (4,000 ) (422,000 ) Fixed assets (1,121,000 ) (1,430,000 ) Net deferred tax liabilities $ (24,000 ) $ (24,000 ) As of December 31, 2018 , the Company had federal, California and Pennsylvania tax net operating loss carryforwards of approximately $383.3 million , $68.6 million and $75.6 million , respectively, net of the net operating losses that will expire due to IRC Section 382 limitations. The federal net operating loss generated in 2018 of $86.5 million will carryforward indefinitely and be available to offset up to 80% of future taxable income each year. The federal, California and Pennsylvania net operating loss carryforwards will begin to expire in 2019 , 2028 and 2021 , respectively, unless previously utilized. In addition, the Company had federal and state research tax credit carryforwards of approximately $13.8 million and $2.7 million , respectively. The federal tax credit carryforwards will begin to expire in 2029. The California research tax credits do not expire. Based upon statute, federal and state losses and credits are expected to expire as follows (in millions): Expiration Date: Federal NOLs State NOLs Federal R&D State R&D 2019 $ 2.4 $ — $ — $ — 2020 1.6 — — — 2021 2.3 0.3 — — 2022 6.0 0.3 — — 2023 4.5 0.4 — — 2024 and thereafter 280.0 143.2 13.8 — Indefinite 86.5 — — 2.7 $ 383.3 $ 144.2 $ 13.8 $ 2.7 Pursuant to Internal Revenue Code (IRC) Sections 382 and 383, annual use of the Company’s net operating loss and research and development credit carryforwards may be limited in the event that a cumulative change in ownership of more than 50% occurs within a three-year period. The Company has completed an IRC Section 382/383 analysis, regarding the limitation of net operating loss and research and development credit carryforwards as of December 31, 2018. As a result of the analysis, the Company estimates that approximately $11.2 million of tax benefits related to NOL and tax credit carryforwards will expire unused. Accordingly, the related NOL and R&D credit carryforwards have been removed from deferred tax assets accompanied by a corresponding reduction of the valuation allowance. Due to the existence of the valuation allowance, limitations created by current and future ownership changes, if any, related to the Company's operations in the United States will not impact its effective tax rate. Any additional ownership changes, may further limit the ability to use the net operating losses and credits carryovers. The Tax Cuts and Jobs Act ("the Act") was enacted on December 22, 2017. The Act included a number of changes to existing U.S. tax laws that impact the Company, most notably a reduction of the U.S. federal corporate tax rate from a maximum of 35% to a flat 21% , effective January 1, 2018. In conjunction with the tax law changes, the SEC staff issued Staff Accounting Bulletin 118 ("SAB 118") to address the application of U.S. GAAP in situations when a registrant does not have the necessary information available, prepared, or analyzed (including computations) in reasonable detail to complete the accounting for certain income tax effects of the Act. In these instances, a company can record provisional amounts in its financial statements for the income tax effects for which a reasonable estimate can be determined. For items for which a reasonable estimate cannot be determined, a company should continue to apply ASC 740 based on the provisions of the tax laws that were in effect immediately prior to the Act being enacted. SAB 118 The Company applied the guidance in SAB 118 when accounting for the enactment-date effects of the Act in 2017 and throughout 2018. At December 31, 2017, the Company had not completed its accounting for all of the enactment-date income tax effects of the Act under ASC 740, Income Taxes, and recorded a provisional amount of $50.0 million , with respect to the remeasurement of deferred tax assets and liabilities, which was reduced by a valuation allowance of $(50.2) million for a net impact of $(0.2) million . At December 31, 2018, the Company has now completed its accounting for all of the enactment-date income tax effects of the Act and no adjustments were made to the provisional amounts recorded at December 31, 2017. The following table summarizes the activity related to the Company's unrecognized tax benefits: Year ended December 31, 2018 2017 2016 Balance at beginning of the year $ 8,313,000 $ 6,855,000 $ 5,455,000 Increases related to current year tax positions 1,319,000 1,532,000 1,183,000 Increases (decreases) related to prior year tax positions — (74,000 ) 217,000 Balance at end of the year $ 9,632,000 $ 8,313,000 $ 6,855,000 The amount of unrecognized tax benefits that, if recognized and realized, would affect the effective tax rate was $8.3 million , $7.1 million and $5.7 million , as of December 31, 2018 , 2017 and 2016, respectively, subject to valuation allowances. The Company has not recorded any interest and penalties on the unrecognized tax positions as the Company has continued to generate net operating losses after accounting for the unrecognized tax benefits. The Company does not anticipate that the total amount of unrecognized tax benefits will significantly increase or decrease within twelve months of the reporting date. The Company and its subsidiaries are subject to U.S. federal income tax as well as income tax in multiple state jurisdictions. With few exceptions, the Company is no longer subject to United States federal income tax examinations for years before 2015 and state and local income tax examinations before 2014. However, to the extent allowed by law, the tax authorities may have the right to examine prior periods where net operating losses were generated and carried forward, and make adjustments up to the amount of the net operating loss carryforward amount. The Company is not currently under Internal Revenue Service (“IRS”), state or local tax examination.

401(k) Plan

401(k) Plan	12 Months Ended
401(k) Plan	Dec. 31, 2018
Retirement Benefits [Abstract]
401(k) Plan	401(k) Plan The Company has adopted a 401(k) Profit Sharing Plan covering substantially all of its employees. The defined contribution plan allows the employees to contribute a percentage of their compensation each year. The Company currently matches 50% of its employees’ contributions, up to 6% of their annual compensation. The Company’s contributions are recorded as expense in the accompanying consolidated statements of operations and totaled $1.2 million , $822,000 and $496,000 for the years ended December 31, 2018 , 2017 and 2016 , respectively.

Related Party Transactions

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2018
Related Party Transaction, Due from (to) Related Party [Abstract]
Related Party Transactions	Related Party Transactions GeneOne Life Sciences The Company owns 1,644,155 shares of common stock in GeneOne as of December 31, 2018 ; one of the Company's directors, Dr. David B. Weiner, acts as a consultant to GeneOne. In 2010, the Company entered into a collaboration and license agreement (the “GeneOne Agreement”) with GeneOne. Under the GeneOne Agreement, the Company granted GeneOne an exclusive license to the Company's SynCon ® universal influenza vaccine delivered with electroporation to be developed in certain countries in Asia (the “Product”). As consideration for the license granted to GeneOne, the Company received an upfront payment of $3.0 million , and is entitled to receive research support, annual license maintenance fees and royalties on net Product sales. The GeneOne Agreement also provides the Company with exclusive rights to supply devices for clinical and commercial purposes (including single use components) to GeneOne for use in the Product. The term of the GeneOne Agreement commenced upon execution and will extend on a country by country basis until the last to expire of all Royalty Periods for the territory (as such term is defined in the GeneOne Agreement) for any Product in that country, unless the GeneOne Agreement is terminated earlier in accordance with its provisions as a result of breach, by mutual agreement, or by GeneOne's right to terminate without cause upon prior written notice. In 2011, the Company entered into a collaborative development and license agreement (the “Hep Agreement”) with GeneOne. Under the Hep Agreement, as originally executed, the Company and GeneOne agreed to co-develop the Company’s SynCon ® therapeutic vaccines for hepatitis B and C infections (the “Hep Products”). Under the terms of the Hep Agreement, GeneOne will receive marketing rights for the Products in Asia, excluding Japan, and in return will fully fund IND-enabling and initial Phase 1 and 2 clinical studies with respect to the Hep Products. The Company will receive from GeneOne payments based on the achievement of clinical milestones and royalties based on sales of the Hep Products in the licensed territories, retaining all commercial rights to the Hep Products in all other territories. In 2013, the Company amended the Hep Agreement to grant back to the Company the SynCon ® therapeutic vaccines targeting hepatitis B, along with all associated rights, from the collaboration in return for certain remuneration including a percentage of license fees. In 2013, the Company further amended the Hep Agreement to in part provide exclusive patent rights to IL-28 technology for use with the Hep Products in Asia, excluding Japan. The Hep Agreement shall terminate upon the later of the expiration or abandonment of the last patent that is a component of the rights or 20 years after the effective date. In May 2015, the Company entered into a Collaborative Development Agreement with GeneOne to co-develop a DNA vaccine for MERS through Phase 1 clinical trials. Under the terms of the agreement, GeneOne will be responsible for funding all preclinical and clinical studies through Phase 1. In return, GeneOne will receive up to a 35% milestone-based ownership interest in the MERS immunotherapy upon achievement of the last milestone event of completion of the Phase 1 safety and immunogenicity study. The collaborative research program shall terminate upon the completion of activities under the development plan, unless sooner terminated. In January 2016, the Company and GeneOne amended the Collaborative Development Agreement for MERS to expand the agreement to test and advance the Company's DNA-based vaccine for preventing and treating Zika virus. GeneOne will be responsible for funding all preclinical and clinical studies through Phase 1. In return, GeneOne will receive up to a 35% milestone-based ownership interest in the Zika immunotherapy upon achievement of the last milestone event of the completion of the Phase 1 safety and immunogenicity study. All other agreement terms remain the same. In December 2017, the Company completed the sale of certain assets related to its compound VGX-1027 to GeneOne for a purchase price of $1.0 million . Revenue recognized from GeneOne consisted of licensing and other fees from the influenza and Zika collaborations. For the years ended December 31, 2018 , 2017 and 2016 , the Company recognized revenue from GeneOne of $342,000 , $551,000 and $1.2 million , respectively. Operating expenses recorded from transactions with GeneOne relate primarily to biologics manufacturing and were $7.0 million , $2.3 million and $2.8 million for the years ended December 31, 2018 , 2017 and 2016 , respectively. At December 31, 2018 and 2017 , the Company had an accounts payable and accrued liability balance of $372,000 and $107,000 , respectively, related to GeneOne and its subsidiaries. At December 31, 2018 and 2017 , $381,000 and $331,000 , respectively, of prepayments made to GeneOne were classified as long-term other assets on the consolidated balance sheet. Plumbline Life Sciences, Inc. The Company owns 395,758 shares of common stock in PLS as of December 31, 2018 ; one of the Company's directors, Dr. David B Weiner, acts as a consultant to PLS. For the years ended December 31, 2018 and 2017 , the Company recognized revenue from PLS of $107,000 and $215,000 , respectively. At December 31, 2018 and 2017 , the Company had an accounts receivable balance of $478,000 and $370,000 , respectively, related to its license agreement with PLS. The Wistar Institute One of the Company's directors, Dr. David B. Weiner, is the Executive Vice President and Director of the Vaccine Center of The Wistar Institute ("Wistar"). In March 2016, the Company entered into collaborative research agreements with Wistar for preventive and therapeutic DNA-based immunotherapy applications and products developed by Dr. Weiner and Wistar for the treatment of cancers and infectious diseases. Under the terms of the agreement, the Company will reimburse Wistar for all direct and indirect costs incurred in the conduct of the collaborative research, not to exceed $3.1 million during the five -year term of the agreement. The Company will have the exclusive right to in-license new intellectual property developed in this agreement. In December 2016 the Company received a $6.1 million sub-grant through Wistar to develop a DNA-based monoclonal antibody against the Zika infection. The Company is also a collaborator with Wistar on an Integrated Preclinical/Clinical AIDS Vaccine Development grant from the NIAID, awarded in 2015. Deferred grant funding recognized from Wistar and recorded as contra-research and development expense, which was classified as grant revenue in the prior year, is related to work performed by the Company on the research sub-contract agreements. For the year ended December 31, 2018 , the Company recorded $3.3 million as contra-research and development expense from Wistar. For the year ended December 31, 2017 , the Company recognized revenue from Wistar of $2.6 million. Research and development expenses recorded from Wistar relate primarily to the collaborative research agreements and sub-contract agreements for the DARPA Ebola grant (see Note 4). Research and development expenses recorded from Wistar for the years ended December 31, 2018 and 2017 were $1.8 million and $2.3 million, respectively. At December 31, 2018 and 2017 , the Company had an accounts receivable balance of $258,000 and $117,000 , respectively, and an accounts payable and accrued liability balance of $554,000 and $820,000 , respectively, related to Wistar.

Quarterly Financial Information

Quarterly Financial Information (Unaudited)	12 Months Ended
Quarterly Financial Information (Unaudited)	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information (Unaudited)	Quarterly Financial Information (Unaudited) The following is a summary of the quarterly results of operations of the Company for the years ended December 31, 2018 and 2017 (unaudited): Quarter Ended Quarter Ended Quarter Ended Quarter Ended December 31, September 30, June 30, March 31, Consolidated Statements of Operations: Revenue: Revenue under collaborative research and development arrangements $ 2,372,600 $ 1,813,287 $ 24,385,852 $ 1,289,046 Revenue under collaborative research and development arrangements with affiliated entity 56,207 184,990 60,319 148,008 Grants and miscellaneous revenue 73,817 2,591 2,590 92,590 Total revenues 2,502,624 2,000,868 24,448,761 1,529,644 Operating Expenses: Research and development 26,365,647 21,851,858 22,462,620 24,577,751 General and administrative 5,636,141 6,791,693 7,189,310 9,698,015 Total operating expenses 32,001,788 28,643,551 29,651,930 34,275,766 Loss from operations (29,499,164 ) (26,642,683 ) (5,203,169 ) (32,746,122 ) Interest and other income, net (169,300 ) 380,987 396,681 312,523 Change in fair value of common stock warrants — 228,665 259,971 (127,841 ) Gain (loss) from investment in affiliated entity (3,293,741 ) 1,017,359 (2,092,608 ) 2,380,423 Net loss before provision for income taxes $ (32,962,205 ) $ (25,015,672 ) $ (6,639,125 ) $ (30,181,017 ) Provision for income taxes — — — (2,169,811 ) Net loss $ (32,962,205 ) $ (25,015,672 ) $ (6,639,125 ) $ (32,350,828 ) Net loss per share Basic $ (0.34 ) $ (0.27 ) $ (0.07 ) $ (0.36 ) Diluted $ (0.34 ) $ (0.27 ) $ (0.08 ) $ (0.36 ) Quarter Ended Quarter Ended Quarter Ended Quarter Ended December 31, September 30, June 30, March 31, Consolidated Statements of Operations: Revenue: Revenue under collaborative research and development arrangements $ 7,409,214 $ 351,272 $ 16,358,316 $ 4,288,586 Revenue under collaborative research and development arrangements with affiliated entity 226,486 129,133 176,879 233,330 Grants and miscellaneous revenue 980,443 1,456,216 2,797,647 5,240,233 Grants and miscellaneous revenue from affiliated entity 171,091 707,922 1,079,282 614,036 Total revenues 8,787,234 2,644,543 20,412,124 10,376,185 Operating Expenses: Research and development 24,641,124 25,510,239 23,878,751 24,542,504 General and administrative 8,033,899 6,319,775 6,169,106 7,767,589 Gain on sale of assets (1,000,000 ) — — — Total operating expenses 31,675,023 31,830,014 30,047,857 32,310,093 Loss from operations (22,887,789 ) (29,185,471 ) (9,635,733 ) (21,933,908 ) Interest and other income, net 509,266 463,346 300,021 340,341 Change in fair value of common stock warrants 579,546 423,296 (312,500 ) 116,477 Gain (loss) from investment in affiliated entity 292,798 (5,835,741 ) 169,096 (1,608,817 ) Net loss $ (21,506,179 ) $ (34,134,570 ) $ (9,479,116 ) $ (23,085,907 ) Net loss per share Basic $ (0.24 ) $ (0.39 ) $ (0.13 ) $ (0.31 ) Diluted $ (0.24 ) $ (0.40 ) $ (0.13 ) $ (0.31 )

Subsequent Events

Subsequent Events	12 Months Ended
Subsequent Events	Dec. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On February 19, 2019 and March 1, 2019, the Company completed a private placement of $78.5 million aggregate principal amount of its 6.50% convertible senior notes due 2024 (the “Notes”). The notes were sold in a private offering to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended. The Company estimates that the net proceeds from the offering were approximately $75.8 million , after deducting the initial purchasers' discount and estimated offering expenses payable by the Company. The notes will be senior unsecured obligations of the Company and will accrue interest payable in cash semi-annually in arrears at a rate of 6.50% per annum. The notes will mature on March 1, 2024, unless earlier converted, redeemed or repurchased. Prior to the close of business on the business day immediately preceding November 1, 2023, the notes will be convertible at the option of the holders only upon the satisfaction of certain circumstances. Thereafter, the notes will be convertible at the option of the holders at any time until the close of business on the scheduled trading day immediately before the maturity date. Upon conversion, the Company will pay or deliver, as the case may be, cash, shares of its common stock or a combination of cash and shares of its common stock, at its election. The initial conversion rate will be 185.8045 shares per $1,000 principal amount of notes (equivalent to an initial conversion price of approximately $5.38 per share), subject to adjustment upon the occurrence of specified events. The Company may not redeem the notes prior to March 1, 2022. On or after March 1, 2022, the Company may redeem all, or any portion, of the notes for cash if the last reported sale price per share of the Company's common stock exceeds 130% of the conversion price on (i) each of at least 20 trading days (whether or not consecutive) during the 30 consecutive trading days ending on, and including, the trading day immediately before the Company sends the related redemption notice; and (ii) the trading day immediately before the date the Company sends such redemption notice. The redemption price will be equal to 100% of the principal amount of the notes to be redeemed, plus accrued and unpaid interest to, but excluding, the redemption date. On February 21, 2019, the Company announced the completion of a spin-out of its previously wholly-owned subsidiary Geneos Therapeutics, Inc. (“Geneos”). On February 21, 2019, Geneos completed the initial closing of a preferred stock financing with outside investors. The Company participated in the preferred stock financing, which was led by an outside investor. The terms of the stock purchase agreement include commitments for additional investments by the Company and the other investors upon the occurrence of a specified regulatory event, as well as an option on the part of the Company and the other investors to purchase additional preferred stock of Geneos upon the achievement of a specified milestone. Following the initial closing of the financing transaction, the Company continues to hold a majority of the outstanding equity, on an as-converted to common stock basis, of Geneos. The Company’s ownership percentage of Geneos would decrease in the event of additional purchases of preferred stock of Geneos by the other investors under the terms of the stock purchase agreement.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation Inovio incurred a net loss attributable to common stockholders of $97.0 million for the year ended December 31, 2018 . Inovio had working capital of $52.5 million and an accumulated deficit of $620.4 million as of December 31, 2018 . The Company has incurred losses in each year since its inception and expects to continue to incur significant expenses and operating losses for the foreseeable future in connection with the research and preclinical and clinical development of its product candidates. In the first quarter of 2019, the Company received net proceeds of $75.8 million from a private placement of $78.5 million aggregate principal amount of its 6.50% convertible senior notes due 2024 (the “Notes”). These proceeds, in addition to the Company’s cash, cash equivalents and short-term investments of $ 81.2 million and long-term investments of $ 9.4 million as of December 31, 2018, are sufficient to support the Company's operations for a period of at least 12 months from the date it issued these financial statements. In addition, the Company could sell up to an additional $71.8 million in shares of its common stock under its At-the-Market Equity Offering Sales Agreement (the “Sales Agreement”), subject to certain conditions set forth in the Sales Agreement. In order to continue to fund future research and development activities, the Company will need to seek additional capital. This may occur through strategic alliance and licensing arrangements and/or future public or private debt or equity financings including use of its Sales Agreement. Although the Company has a history of equity financings including the receipt of net proceeds of $29.2 million under the current Sales Agreement and a prior agreement during the year ended December 31, 2018 and net proceeds of $94.3 million from an underwritten public offering and a previous at-the-market sales facility during the year ended December 31, 2017 , sufficient funding may not be available, or if available, may be on terms that significantly dilute or otherwise adversely affect the rights of existing stockholders. If adequate funds are not available in the future, the Company may need to delay, reduce the scope of or put on hold one or more of its clinical and/or preclinical programs. The Company’s ability to continue its operations is dependent upon its ability to obtain additional capital in the future and achieve profitable operations. The Company expects to continue to rely on outside sources of financing to meet its capital needs and the Company may never achieve positive cash flow. These consolidated financial statements do not include any adjustments to the specific amounts and classifications of assets and liabilities, which might be necessary should Inovio be unable to continue as a going concern. Inovio’s consolidated financial statements as of and for the year ended December 31, 2018 have been prepared on a going concern basis, which contemplates the realization of assets and the settlement of liabilities and commitments in the normal course of business for the foreseeable future. The Company has evaluated subsequent events after the balance sheet date through the date it issued these financial statements.
Consolidation	Consolidation These consolidated financial statements include the accounts of Inovio Pharmaceuticals, Inc. and its subsidiaries. The Company consolidates its wholly-owned subsidiaries Genetronics, Inc., VGX Pharmaceuticals Inc. ("VGX"), and Geneos Therapeutics, Inc. ("Geneos"), and records a non-controlling interest for 15% of VGX Animal Health, Inc., a subsidiary of VGX. All intercompany accounts and transactions have been eliminated upon consolidation.
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business as one segment operating primarily within the United States.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosures of contingent assets and liabilities at the date of the consolidated financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments, that potentially subject the Company to concentrations of credit risk consist primarily of cash and short-term investments. The Company limits its exposure to credit loss by placing its cash and investments with high credit quality financial institutions. Additionally, the Company has established guidelines regarding diversification of its investments and their maturities which are designed to maintain principal and maximize liquidity.
Fair value of Financial Instruments	Fair value of Financial Instruments The Company’s financial instruments consist principally of cash equivalents, short-term investments and investments in affiliated entities. The carrying amounts of cash equivalents approximate the related fair values due to the short-term maturities of these instruments. Investments are recorded at fair value, based on current market valuations. After the adoption of ASU No. 2016-01 on January 1, 2018, unrealized gains and losses on the Company's equity investment in its affiliated entity Plumbline Life Sciences, Inc. ("PLS") are reported in the consolidated statement of operations as a gain (loss) on investment in affiliated entities
Cash and Cash Equivalents	Cash and Cash Equivalents Cash equivalents are considered by the Company to be highly liquid investments purchased with original maturities of three months or less from the date of purchase. Cash and cash equivalents included certain money market accounts at December 31, 2018 and 2017 .
Investments	Investments The Company defines investments as income-yielding securities that can be readily converted into cash or equity investments classified as available-for-sale. Investments included mutual funds. United States corporate debt securities and equity investments in the Company’s affiliated entities, PLS and GeneOne at December 31, 2018 . Investments included mutual funds, United States corporate debt securities and an equity investment in the Company's affiliated entity PLS at December 31, 2017 .
Accounts Receivable	Accounts Receivable Accounts receivable are recorded at invoiced amounts and do not bear interest. The Company performs ongoing credit evaluations of its customers’ financial condition. Credit is extended to customers as deemed necessary and generally does not require collateral. Management believes that the risk of loss is significantly reduced due to the quality and financial position of the Company's customers.
Fixed Assets	Fixed Assets Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful life of the assets, generally three to five years. Leasehold improvements are amortized over the shorter of the remaining term of the related leases or the estimated economic useful lives of the improvements. Repairs and maintenance are expensed as incurred.
Long-Lived Assets	Long-Lived Assets All long-lived assets are reviewed for impairment in value when changes in circumstances dictate, based upon undiscounted future operating cash flows, and appropriate losses are recognized and reflected in current earnings, to the extent the carrying amount of an asset exceeds its estimated fair value determined by the use of appraisals, discounted cash flow analyses or comparable fair values of similar assets.
Valuation of Intangible Assets and Goodwill	Valuation of Intangible Assets and Goodwill Intangible assets are amortized over their estimated useful lives ranging from two to 18 years. Acquired intangible assets are continuously being developed for the future economic viability contemplated at the time of acquisition. The Company is concurrently conducting preclinical studies and clinical trials using the acquired intangibles and has entered into licensing agreements for the use of these acquired intangibles. Historically, the Company has recorded patents at cost and amortized these costs using the straight-line method over the expected useful lives of the patents or 17 years, whichever is less. Patent cost consists of the consideration paid for patents and related legal costs. Effective as of the acquisition of VGX in 2009, all new patent costs are expensed as incurred, with patent costs capitalized as of that date continuing to be amortized over the expected life of the patent. License costs are recorded based on the fair value of consideration paid and are amortized using the straight-line method over the shorter of the expected useful life of the underlying patents or the term of the related license agreement to the extent the license has an alternative future use. As of December 31, 2018 and 2017 , the Company’s intangible assets resulting from the acquisition of VGX, as well as the acquisitions of two other companies, Inovio AS and Bioject Medical Technologies, Inc. ("Bioject"), and additional intangibles including previously capitalized patent costs and license costs, net of accumulated amortization, totaled $4.8 million and $ 6.0 million , respectively. The determination of the value of intangible assets requires management to make estimates and assumptions that affect the Company’s consolidated financial statements. The Company assesses potential impairments to intangible assets when there is evidence that events or changes in circumstances indicate that the carrying amount of an asset may not be recovered. The Company’s judgments regarding the existence of impairment indicators and future cash flows related to intangible assets are based on operational performance of its acquired businesses, market conditions and other factors. If impairment is indicated, the Company will reduce the carrying value of the intangible asset to fair value. While current and historical operating and cash flow losses are potential indicators of impairment, the Company believes the future cash flows to be received from its intangible assets will exceed the intangible assets’ carrying value, and accordingly, the Company has not recognized any impairment losses through December 31, 2018 . Goodwill represents the excess of acquisition cost over the fair value of the net assets of acquired businesses. Goodwill is reviewed for impairment at least annually at November 30, or more frequently if an event occurs indicating the potential for impairment. During its goodwill impairment review, the Company may assess qualitative factors to determine whether it is more likely than not that the fair value of its reporting unit is less than its carrying amount, including goodwill. The qualitative factors include, but are not limited to, macroeconomic conditions, industry and market considerations, and the overall financial performance of the Company. If, after assessing the totality of these qualitative factors, the Company determines that it is not more likely than not that the fair value of its reporting unit is less than its carrying amount, then no additional assessment is deemed necessary. Otherwise, the Company proceeds to perform the two-step test for goodwill impairment. The first step involves comparing the estimated fair value of the reporting unit with its carrying value, including goodwill. If the carrying amount of the reporting unit exceeds its fair value, the Company performs the second step of the goodwill impairment test to determine the amount of loss, which involves comparing the implied fair value of the goodwill to the carrying value of the goodwill. The Company may also elect to bypass the qualitative assessment in a period and elect to proceed to perform the first step of the goodwill impairment test. The Company performed its annual assessment for goodwill impairment as of November 30, 2018 , identifying no impairment. Although there are inherent uncertainties in this assessment process, the estimates and assumptions the Company is using are consistent with its internal planning. If these estimates or their related assumptions change in the future, the Company may be required to record an impairment charge on all or a portion of its goodwill and intangible assets. Furthermore, the Company cannot predict the occurrence of future impairment triggering events nor the impact such events might have on its reported asset values. Future events could cause the Company to conclude that impairment indicators exist and that goodwill or other intangible assets associated with its acquired businesses are impaired. Any resulting impairment loss could have an adverse impact on the Company’s results of operations.
Income Taxes	Income Taxes The Company recognizes deferred tax assets and liabilities for temporary differences between the financial reporting basis and the tax basis of the Company’s assets and liabilities along with net operating loss and tax credit carry forwards. The Company records a valuation allowance against its deferred tax assets to reduce the net carrying value to an amount that it believes is more likely than not to be realized. When the Company establishes or reduces the valuation allowance against its deferred tax assets, its provision for income taxes will increase or decrease, respectively, in the period such determination is made. Valuation allowances against the Company’s deferred tax assets were $115.0 million and $94.0 million at December 31, 2018 and 2017 , respectively. Changes in the valuation allowances, when they are recognized in the provision for income taxes, are included as a component of the estimated annual effective tax rate.
Revenue Recognition	License Fees If a license to intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company will recognize revenues from non-refundable, up-front fees allocated to the license when the license is transferred to the licensee and the licensee is able to use and benefit from the license. For licenses that are bundled with other promises, the Company will utilize judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments At the inception of each arrangement that includes milestone payments (variable consideration), the Company evaluates whether the milestones are considered probable of being reached and estimates the amount to be included in the transaction price using the most likely amount method. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Milestone payments that are not within the Company's or its collaboration partner’s control, such as regulatory approvals, are generally not considered probable of being achieved until those approvals are received. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis, for which the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achieving such milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect license, collaboration or other revenues and earnings in the period of adjustment. Royalties For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and for which the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur, or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its collaborative arrangements. Under certain collaborative arrangements, the Company has been reimbursed for a portion of its research and development ("R&D") expenses, including costs of drug supplies. When these R&D services are performed under a reimbursement or cost sharing model with its collaboration partner, the Company records these reimbursements as a reduction of R&D expense in its consolidated statements of operations. Revenue Recognition Effective January 1, 2018, the Company adopted Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (“Topic 606”) using the modified retrospective method which consisted of applying and recognizing the cumulative effect of Topic 606 at the date of initial application. Topic 606 supersedes the revenue recognition requirements in Accounting Standards Codification (“ASC”) Topic 605, Revenue Recognition (“Topic 605”), including most industry-specific revenue recognition guidance throughout the Industry Topics of the ASC. All periods prior to the adoption date of Topic 606 have not been restated to reflect the impact of the adoption of Topic 606, but continue to be accounted for and presented under Topic 605. The following paragraphs in this section describe the Company's revenue recognition accounting policies under Topic 606 upon adoption on January 1, 2018. Refer to Note 2 to the consolidated financial statements included in the Company's Annual Report on Form 10-K for the year ended December 31, 2017 for revenue recognition accounting policies under Topic 605. The Company recognizes revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which it expects to be entitled in exchange for those goods or services. To determine revenue recognition for contracts with customers, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies its performance obligations. At contract inception, the Company assesses the goods or services agreed upon within each contract and assess whether each good or service is distinct and determine those that are performance obligations. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when (or as) the performance obligation is satisfied. Collaborative Arrangements The Company enters into collaborative arrangements with partners that typically include payment of one or more of the following: (i) license fees; (ii) milestone payments related to the achievement of developmental, regulatory, or commercial goals; and (iii) royalties on net sales of licensed products. Where a portion of non-refundable, upfront fees or other payments received are allocated to continuing performance obligations under the terms of a collaborative arrangement, they are recorded as deferred revenue and recognized as revenue when (or as) the underlying performance obligation is satisfied. As part of the accounting for these arrangements, the Company must develop estimates and assumptions that require judgment of management to determine the underlying stand-alone selling price for each performance obligation which determines how the transaction price is allocated among the performance obligation. The standalone selling price may include items such as forecasted revenues, development timelines, discount rates and probabilities of technical and regulatory success. The Company evaluates each performance obligation to determine if it can be satisfied at a point in time or over time. In addition, variable consideration must be evaluated to determine if it is constrained and, therefore, excluded from the transaction price.
Grant	Grants The Company has determined that as of January 1, 2018, accounting for the Company’s various grant agreements falls under the contributions guidance under Subtopic 958-605, Not-for-Profit Entities-Revenue Recognition , which is outside the scope of Topic 606, as the government agencies granting the Company funds are not receiving reciprocal value for their contributions. Beginning on January 1, 2018, all contributions received from current grant agreements are recorded as a contra expense as opposed to revenue on the consolidated statement of operations.
Research and Development Expenses	Research and Development Expenses The Company’s activities have largely consisted of research and development efforts related to developing electroporation delivery technologies and DNA immunotherapies and vaccines. Research and development expenses consist of expenses incurred in performing research and development activities including salaries and benefits, facilities and other overhead expenses, clinical trials, contract services and other outside expenses. Research and development expenses are charged to operations as they are incurred. These expenses result from the Company's independent research and development efforts as well as efforts associated with collaborations and licensing arrangements. The Company reviews and accrues clinical trial expense based on work performed, which relies on estimates of total costs incurred based on patient enrollment, completion of studies and other events. The Company follows this method since reasonably dependable estimates of the costs applicable to various stages of a research agreement or clinical trial can be made. Accrued clinical trial costs are subject to revisions as trials progress. Revisions are charged to expense in the period in which the facts that give rise to the revision become known. Historically, revisions have not resulted in material changes to research and development expense; however, a modification in the protocol of a clinical trial or cancellation of a trial could result in a charge to the Company's results of operations.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed by dividing the net loss for the year by the weighted average number of common shares outstanding during the year. Diluted net loss per share is calculated in accordance with the treasury stock method and reflects the potential dilution that would occur if securities or other contracts to issue common stock were exercised or converted to common stock. The calculation of diluted net loss per share requires that, to the extent the average market price of the underlying shares for the reporting period exceeds the exercise price of the options, warrants or other securities and the presumed exercise of such securities are dilutive to net loss per share for the period, an adjustment to net loss used in the calculation is required to remove the change in fair value of such securities from the numerator for the period. Likewise, an adjustment to the denominator is required to reflect the related dilutive shares, if any, under the treasury stock method.
Leases	Leases Leases are classified as either capital or operating leases. Leases which transfer substantially all of the benefits and risks incidental to the ownership of assets are accounted for as if there was an acquisition of an asset and incurrence of an obligation at the inception of the lease. All other leases are accounted for as operating leases. Inovio’s Plymouth Meeting, PA headquarters and San Diego, CA facility leases, which have escalating payments, are expensed on a straight-line basis over the term of the lease. The allowance provided by the lessor for non-structural, normal leasehold improvements are considered tenant incentives and are amortized on a straight-line basis over the term of the lease. These leases represent the primary expense and commitment as indicated in Note 12, “Commitments”. Other leases exist for office machinery, such as copiers, wherein lease expense is recorded as incurred.
Stock-Based Compensation	Stock-Based Compensation The Company incurs stock-based compensation expense related to restricted stock units and stock options. The fair value of restricted stock is determined by the closing price of the Company's common stock reported on the Nasdaq Global Select Market on the date of grant. The Company estimates the fair value of stock options granted using the Black-Scholes option pricing model. The Black-Scholes option pricing model was developed for use in estimating the fair value of traded options, which have no vesting restrictions and are fully transferable. In addition, option valuation models require the input of subjective assumptions, including the expected stock price volatility and expected option life. The Company amortizes the fair value of the awards on a straight-line basis over the requisite vesting period of the awards. Expected volatility is based on historical volatility. The expected life of options granted is based on historical expected life. The risk-free interest rate is based on the U.S. Treasury yield in effect at the time of grant. The dividend yield is based on the fact that no dividends have been paid historically and none are currently expected to be paid in the foreseeable future. Upon adoption of ASU 2016-09 on January 1, 2017, the Company elected to remove the forfeiture rate from the calculation and recorded a cumulative catch-up adjustment to accumulated deficit with a corresponding offset to additional paid-in-capital of $312,000 . Previously, the forfeiture rate was based on historical data and the Company recorded stock-based compensation expense only for those awards that were expected to vest.
Recent Accounting Pronouncements - Recently Adopted, Recent Accounting Pronouncements	Recent Accounting Pronouncements - Recently Adopted The recent accounting pronouncements below may have a significant effect on the Company's financial statements. Recent accounting pronouncements that are not anticipated to have an impact on or are unrelated to the Company's financial condition, results of operations, or related disclosures are not discussed. ASU No. 2014-09. In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers ("Topic 606”), which amended the existing accounting standards for revenue recognition, outlines a comprehensive revenue recognition model and supersedes most current revenue recognition guidance. The new standard requires a company to recognize revenue upon transfer of goods or services to a customer at an amount that reflects the expected consideration to be received in exchange for those goods or services. The amended guidance defines a five-step approach for recognizing revenue, which will require a company to use more judgment and make more estimates than under the current guidance. The Company adopted this new standard effective January 1, 2018, using the modified retrospective transition method. The impact of adoption of Topic 606 on the Company's existing agreements was as follows: Collaboration Agreement with AstraZeneca The Company determined that no cumulative catch-up adjustment was required. Grant Agreements The Company determined that, as of January 1, 2018, accounting for the Company’s various grant agreements falls under the contributions guidance under Subtopic 958-605 , Not-for-Profit Entities-Revenue Recognition , which is outside the scope of Topic 606, as the government agencies granting the Company funds are not receiving reciprocal value for their contributions. Beginning on January 1, 2018, all contributions received from current grant agreements have been recorded as a contra-expense as opposed to revenue on the consolidated statements of operations. For the year ended December 31, 2018 , $9.5 million would have been recorded as grant revenue but under the new guidance was instead recorded as a reduction to research and development expense. The following table illustrates the impact that adopting Topic 606 has had on the Company's reported results in the consolidated statements of operations for the year ended December 31, 2018 . Balances Without Adoption of Topic 606 for the Year Ended December 31, 2018 Impact of Adopting Topic 606 As Reported for the Year Ended December 31, 2018 Revenues: Revenue under collaborative research and development arrangements $ 29,860,785 $ — $ 29,860,785 Revenue under collaborative research and development arrangements with affiliated entities 449,524 — 449,524 Grants and miscellaneous revenue 6,315,116 (6,143,528 ) 171,588 Grants and miscellaneous revenue from affiliated entity 3,348,177 (3,348,177 ) — Total revenues 39,973,602 (9,491,705 ) 30,481,897 Operating expenses: Research and development 104,749,581 (9,491,705 ) 95,257,876 General and administrative 29,315,159 — 29,315,159 Total operating expenses $ 134,064,740 $ (9,491,705 ) $ 124,573,035 ASU No. 2016-01. In January 2016, the FASB issued ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities . The amended guidance requires the Company to measure and record equity investments, except those accounted for under the equity method of accounting that have a readily determinable fair value, at fair value and for the Company to recognize the changes in fair value in its consolidated statements of operations, instead of recognizing unrealized gains and losses through accumulated other comprehensive income (loss), as done under the previous guidance. The amended guidance also changes several disclosure requirements for financial instruments, including the methods and significant assumptions used to estimate fair value. The standard was effective for annual reporting periods beginning after December 15, 2017, including interim periods within those annual reporting periods. The Company adopted this guidance on January 1, 2018 and recorded a $231,000 cumulative effect adjustment to reclassify the cumulative unrealized gain, net of tax effect, from its investment in PLS from accumulated other comprehensive loss to accumulated deficit. After the adoption of ASU No. 2016-01, the Company recorded a gain on investment in affiliated entity related to PLS of $699,000 on the consolidated statement of operations for the year ended December 31, 2018 . The cumulative effect of the changes made to the Company's consolidated balance sheet as of January 1, 2018 for the adoption of ASU No. 2016-01 are included in the table below: Equity: Balance at December 31, 2017 Adjustments due to ASU No. 2016-01 Balance at January 1, 2018 Accumulated deficit $ (523,356,317 ) $ 231,366 $ (523,124,951 ) Accumulated other comprehensive loss $ (117,005 ) $ (231,366 ) $ (348,371 ) Recent Accounting Pronouncements ASU No. 2016-02. In February 2016, the FASB issued ASU No. 2016-02, Leases ("ASU 2016-02"). ASU 2016-02 is aimed at making leasing activities more transparent and comparable, and requires lessees to recognize substantially all leases on their balance sheet as a right-of-use asset and a corresponding lease liability, including leases currently accounted for as operating leases. The Company will adopt ASU 2016-02 on January 1, 2019. The Company anticipates recognizing a right-of-use asset and a lease liability on its consolidated balance sheet for the discounted value for future lease payment from the adoption of this ASU. The Company is currently evaluating the full impact of the adoption of ASU 2016-02

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
Summary of Significant Accounting Policies (Tables)	Dec. 31, 2018
Accounting Policies [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	The following tables reconcile the components of the numerator and denominator included in the calculations of diluted net loss per share: Year Ended December 31, 2018 2017 2016 Numerator Net loss (numerator for use in basic net loss per share) $ (96,967,830 ) $ (88,205,772 ) $ (73,740,339 ) Adjustment for decrease in fair value of warrant liability — (806,819 ) — Numerator for use in diluted net loss per share $ (96,967,830 ) $ (89,012,591 ) $ (73,740,339 ) Denominator Weighted average number of common shares outstanding (denominator for use in basic net loss per share) 92,539,997 81,777,493 73,214,766 Effect of dilutive potential common shares — 140,529 — Denominator for use in diluted net loss per share 92,539,997 81,918,022 73,214,766 Net loss per share, diluted $ (1.05 ) $ (1.09 ) $ (1.01 ) Net loss per share, basic $ (1.05 ) $ (1.08 ) $ (1.01 )
Summary of common shares that were excluded from the diluted net loss per share calculation because of their anti-dilutive effect	The following table summarizes potential shares of common stock that were excluded from diluted net loss per share calculation because of their anti-dilutive effect: Year Ended December 31, 2018 2017 2016 Options to purchase common stock 8,752,677 7,694,870 6,806,183 Warrants to purchase common stock — — 284,091 Restricted stock units 1,688,017 1,234,168 798,834 Convertible preferred stock 8,456 8,456 8,456 Total 10,449,150 8,937,494 7,897,564
Summary of assumptions used to estimate the fair value of stock options	The weighted average assumptions used in the Black-Scholes model for option grants to employees and directors are presented below: Year Ended December 31, 2018 2017 2016 Risk-free interest rate 2.73% 2.20% 0.91% Expected volatility 72% 73% 76% Expected life in years 6 6 5 Dividend yield — — — Forfeiture rate N/A N/A 7% Assumptions used in the Black-Scholes model for non-employees are presented below: Year Ended December 31, 2018 2017 2016 Risk-free interest rate 2.6%-3.0% 2.4%-2.6% 2.3%-2.5% Expected volatility 68%-101% 97%-102% 71%-104% Expected life in years 9-10 9-10 7-10 Dividend yield — — —
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	The following table illustrates the impact that adopting Topic 606 has had on the Company's reported results in the consolidated statements of operations for the year ended December 31, 2018 . Balances Without Adoption of Topic 606 for the Year Ended December 31, 2018 Impact of Adopting Topic 606 As Reported for the Year Ended December 31, 2018 Revenues: Revenue under collaborative research and development arrangements $ 29,860,785 $ — $ 29,860,785 Revenue under collaborative research and development arrangements with affiliated entities 449,524 — 449,524 Grants and miscellaneous revenue 6,315,116 (6,143,528 ) 171,588 Grants and miscellaneous revenue from affiliated entity 3,348,177 (3,348,177 ) — Total revenues 39,973,602 (9,491,705 ) 30,481,897 Operating expenses: Research and development 104,749,581 (9,491,705 ) 95,257,876 General and administrative 29,315,159 — 29,315,159 Total operating expenses $ 134,064,740 $ (9,491,705 ) $ 124,573,035 The cumulative effect of the changes made to the Company's consolidated balance sheet as of January 1, 2018 for the adoption of ASU No. 2016-01 are included in the table below: Equity: Balance at December 31, 2017 Adjustments due to ASU No. 2016-01 Balance at January 1, 2018 Accumulated deficit $ (523,356,317 ) $ 231,366 $ (523,124,951 ) Accumulated other comprehensive loss $ (117,005 ) $ (231,366 ) $ (348,371 )

Investments (Tables)

Investments (Tables)	12 Months Ended
Investments (Tables)	Dec. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Summary of investments	The following is a summary of available-for-sale securities as of December 31, 2018 and 2017 : As of December 31, 2018 Contractual Maturity (in years) Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value Mutual funds --- $ 57,842,955 $ — $ (528,084 ) $ 57,314,871 US corporate debt securities Less than 2 224,633 — (652 ) 223,981 Total investments $ 58,067,588 $ — $ (528,736 ) $ 57,538,852 As of December 31, 2017 Contractual Maturity (in years) Cost Gross Unrealized Gains Gross Unrealized Losses Fair Market Value Mutual funds --- $ 68,776,165 $ 42,097 $ (252,373 ) $ 68,565,889 US corporate debt securities Less than 2 35,210,121 3,032 (140,198 ) 35,072,955 Investment in affiliated entity (PLS) --- — 2,325,079 — 2,325,079 Total investments $ 103,986,286 $ 2,370,208 $ (392,571 ) $ 105,963,923

Marketable Securities and Fai_2

Marketable Securities and Fair Value Measurements (Tables)	12 Months Ended
Marketable Securities and Fair Value Measurements (Tables)	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Financial assets and liabilities measured at fair value on a recurring basis	The following table presents the Company’s assets that are measured at fair value on a recurring basis, and are determined using the following inputs as of December 31, 2018 : Fair Value Measurements at December 31, 2018 Total Quoted Prices in Active Markets (Level 1) Significant Other Unobservable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds $ 9,646,507 $ 9,646,507 $ — $ — Mutual funds 57,314,871 — 57,314,871 — US corporate debt securities 223,981 — 223,981 — Investments in affiliated entities 9,405,913 9,405,913 — — Total assets $ 76,591,272 $ 19,052,420 $ 57,538,852 $ — The following table presents the Company’s assets and liabilities that are measured at fair value on a recurring basis, and are determined using the following inputs as of December 31, 2017 : Fair Value Measurements at December 31, 2017 Total Quoted Prices in Active Markets (Level 1) Significant Other Unobservable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Assets: Money market funds $ 9,843,482 $ 9,843,482 $ — $ — Mutual funds 68,565,889 — 68,565,889 — US corporate debt securities 35,072,955 — 35,072,955 — Investments in affiliated entities 11,394,480 11,394,480 — — Total assets $ 124,876,806 $ 21,237,962 $ 103,638,844 $ — Liabilities: Common stock warrants $ 360,795 $ — $ — $ 360,795 Total liabilities $ 360,795 $ — $ — $ 360,795
Assumptions used to estimate the fair values of the common stock warrants	The assumptions used to estimate the fair value of common stock warrants at December 31, 2017 is presented below: Year Ended December 31, 2017 Risk-free interest rate 1.75% Expected volatility 55% Expected life in years 0.70 Dividend yield —
Changes in fair value of the financial liabilities	The following table presents the changes in fair value of the Company’s total Level 3 financial liabilities for the years ended December 31, 2018 and 2017 : Year Ended December 31, 2018 2017 Balance at beginning of year $ 360,795 $ 1,167,614 Decrease in fair value included in change in fair value of common stock warrants (360,795 ) (806,819 ) Balance at end of year $ — $ 360,795

Major Customers and Concentra_2

Major Customers and Concentration of Credit Risk (Tables)	12 Months Ended
Major Customers and Concentration of Credit Risk (Tables)	Dec. 31, 2018
Risks and Uncertainties [Abstract]
Schedule of major customers and concentration risks	Customer 2018 Revenue % of Total Revenue 2017 Revenue % of Total Revenue 2016 Revenue % of Total Revenue ApolloBio $ 23,000,000 75 % $ — — % $ — — % AstraZeneca 6,850,424 23 22,269,773 53 1,518,639 4 DARPA — — 9,983,927 24 26,602,183 75 Roche — — 6,107,254 14 4,917,929 14 GeneOne (affiliated entity) 342,386 1 551,208 1 1,188,432 4 All other 289,087 1 3,307,924 8 1,141,178 3 Total revenue $ 30,481,897 100 % $ 42,220,086 100 % $ 35,368,361 100 %

Fixed Assets (Tables)

Fixed Assets (Tables)	12 Months Ended
Fixed Assets (Tables)	Dec. 31, 2018
Property, Plant and Equipment [Abstract]
Schedule of fixed assets	Fixed assets at December 31, 2018 and 2017 consist of the following: Cost Accumulated Depreciation and Amortization Net Book Value As of December 31, 2018 Leasehold improvements $ 14,909,341 $ (3,464,444 ) $ 11,444,897 Laboratory equipment 4,031,965 (2,425,854 ) 1,606,111 Office furniture and fixtures 3,198,803 (1,767,653 ) 1,431,150 Computer equipment and other 3,808,824 (2,341,968 ) 1,466,856 $ 25,948,933 $ (9,999,919 ) $ 15,949,014 As of December 31, 2017 Leasehold improvements $ 14,553,993 $ (2,042,871 ) $ 12,511,122 Laboratory equipment 3,787,578 (1,724,946 ) 2,062,632 Office furniture and fixtures 3,366,896 (1,471,705 ) 1,895,191 Computer equipment and other 3,718,266 (1,867,035 ) 1,851,231 $ 25,426,733 $ (7,106,557 ) $ 18,320,176

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	12 Months Ended
Goodwill and Intangible Assets (Tables)	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Summary of intangible assets by major asset class	The following sets forth goodwill and intangible assets by major asset class: December 31, 2018 December 31, 2017 Useful Life (Yrs) Gross Accumulated Amortization Net Book Value Gross Accumulated Amortization Net Book Value Indefinite lived: Goodwill(a) $ 10,513,371 $ — $ 10,513,371 $ 10,513,371 $ — $ 10,513,371 Definite lived: Patents 8 – 17 5,802,528 (5,742,079 ) 60,449 5,802,528 (5,681,673 ) 120,855 Licenses 8 – 17 1,323,761 (1,219,357 ) 104,404 1,323,761 (1,190,609 ) 133,152 CELLECTRA ® (b) 5 – 11 8,106,270 (7,679,190 ) 427,080 8,106,270 (7,252,108 ) 854,162 GHRH(b) 11 335,314 (303,630 ) 31,684 335,314 (271,948 ) 63,366 Bioject (c) 2 – 15 5,100,000 (1,882,222 ) 3,217,778 5,100,000 (1,405,556 ) 3,694,444 Other(d) 18 4,050,000 (3,131,250 ) 918,750 4,050,000 (2,906,250 ) 1,143,750 Total intangible assets 24,717,873 (19,957,728 ) 4,760,145 24,717,873 (18,708,144 ) 6,009,729 Total goodwill and intangible assets $ 35,231,244 $ (19,957,728 ) $ 15,273,516 $ 35,231,244 $ (18,708,144 ) $ 16,523,100 (a) Goodwill was recorded from the Inovio AS acquisition in January 2005, the acquisition of VGX in June 2009 and the acquisition of Bioject in April 2016 for $3.9 million , $6.2 million and $400,000 , respectively. (b) CELLECTRA ® and GHRH are developed technologies which were recorded from the acquisition of VGX. (c) Bioject intangible assets represent the estimated fair value of developed technology and intellectual property which were recorded from the Bioject asset acquisition. (d) Other intangible assets represent the estimated fair value of acquired intellectual property from the Inovio AS acquisition.
Schedule of finite-lived intangible assets, future amortization expense	Amortization expense related to intangible assets at December 31, 2018 is expected to be incurred as follows: Year ending December 31, 2019 $ 1,066,251 2020 547,081 2021 520,414 2022 492,818 2023 275,803 Thereafter 1,857,778 $ 4,760,145

Accounts Payable and Accrued _2

Accounts Payable and Accrued Expenses (Tables)	12 Months Ended
Accounts Payable and Accrued Expenses (Tables)	Dec. 31, 2018
Payables and Accruals [Abstract]
Schedule of accounts payable and accrued expenses	Accounts payable and accrued expenses at December 31, 2018 and 2017 consist of the following: As of December 31, 2018 2017 Trade accounts payable $ 10,043,816 $ 7,564,830 Accrued compensation 9,466,821 7,997,152 Accrued subcontract costs 83,812 3,746,937 Other accrued expenses 3,540,284 3,969,879 $ 23,134,733 $ 23,278,798

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
Stockholders' Equity (Tables)	Dec. 31, 2018
Stockholders' Equity Note [Abstract]
Summary of preferred stock authorized, issued and outstanding	Shares Outstanding as of December 31, Shares Authorized Shares Issued 2018 2017 Series C Preferred Stock, par $0.001 1,091 1,091 23 23
Summary of warrants outstanding	The following table summarizes the warrants outstanding as of December 31, 2018 and 2017 : As of December 31, 2018 As of December 31, 2017 Issued in Connection With: Exercise Price Expiration Date Number of Warrants Common Stock Warrant Liability Number of Warrants Common Stock Warrant Liability March 2013 financing $ 3.17 September 12, 2018 — $ — 284,091 $ 360,795 Total — $ — 284,091 $ 360,795
Schedule of shares authorized under stock option plans, by exercise price range	The following table summarizes total stock options outstanding at December 31, 2018 : Options Outstanding Options Exercisable Exercise Price Shares Underlying Options Outstanding Weighted-Average Remaining Contractual Life (in Years) Weighted Average Exercise Price Shares Underlying Options Exercisable Weighted Average Exercise Price $1.48-$3.00 879,321 3.7 $ 2.26 879,321 $ 2.26 $3.01-$6.00 2,558,453 7.9 $ 4.38 974,723 $ 4.44 $6.01-$9.00 4,394,357 6.7 $ 7.11 3,408,953 $ 7.20 $9.01-$12.00 257,836 6.9 $ 9.79 228,788 $ 9.81 $12.01-$15.00 662,710 5.2 $ 12.96 662,710 $ 12.96 8,752,677 6.7 $ 6.35 6,154,495 $ 6.78
Schedule of stock options, activity	Stock option activity under the Company’s equity incentive plans during the year ended December 31, 2018 was as follows: Number of Shares Weighted-Average Exercise Price Balance, December 31, 2017 7,694,870 $ 6.77 Granted 2,176,935 4.32 Exercised (472,762 ) 3.21 Cancelled (646,366 ) 6.83 Balance, December 31, 2018 8,752,677 $ 6.35
Schedule of Share-based Compensation, Restricted Stock Units Award Activity	Restricted stock unit activity under the Company’s equity incentive plans during the year ended December 31, 2018 was as follows: Number of Shares Weighted-Average Exercise Price Balance, December 31, 2017 1,234,168 $ — Granted 1,070,106 — Vested (539,468 ) — Cancelled (76,789 ) — Balance, December 31, 2018 1,688,017 $ —

Commitments (Tables)

Commitments (Tables)	12 Months Ended
Commitments (Tables)	Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future minimum lease payments under non-cancelable operating leases	Future minimum lease payments under non-cancelable operating leases as of December 31, 2018 are as follows: Year ending December 31, 2019 $ 3,756,000 2020 3,891,000 2021 3,979,000 2022 4,052,000 2023 4,023,000 Thereafter 15,952,000 Total $ 35,653,000

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
Income Taxes (Tables)	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Schedule of components of income tax expense (benefit)	The components of the provision for income taxes are presented in the following table: Year Ended December 31, 2018 2017 2016 Current: Federal $ — $ — $ — State — — — Foreign 2,170,000 — — 2,170,000 — — Deferred: Federal — — State — — — Foreign — — — — — — $ 2,170,000 $ — $ —
Schedule of effective income tax rate reconciliation	The reconciliation of income taxes attributable to continuing operations computed at the statutory tax rates to income tax expense (recovery), using a 21% statutory tax rate for December 31, 2018, and 35% statutory tax rate for December 31, 2017 and 2016, is as follows: Year Ended December 31, 2018 2017 2016 Income (benefit) taxes at statutory rates $ (19,908,000 ) $ (30,872,000 ) $ (25,809,000 ) State income tax, net of federal benefit (4,000 ) (4,000 ) (4,000 ) Foreign income taxes 2,170,000 — — Change in valuation allowance 20,898,000 (20,965,000 ) 29,678,000 Research and development tax credits (3,170,000 ) (3,456,000 ) (3,117,000 ) Fair value warrant (76,000 ) (282,000 ) (47,000 ) Stock compensation 1,094,000 2,332,000 113,000 Uncertain tax positions 1,268,000 846,000 1,367,000 Expired NOLs and credits 2,176,000 454,000 4,269,000 Limited NOLs and credits (2,176,000 ) (165,000 ) (6,456,000 ) Change in tax rates — 50,019,000 (495,000 ) Other (102,000 ) 2,093,000 501,000 $ 2,170,000 $ — $ —
Schedule of deferred tax assets and liabilities	Significant components of the Company’s deferred tax assets and liabilities as of December 31, 2018 and 2017 are shown below: As of December 31, 2018 2017 Deferred tax assets: Capitalized research expense $ 7,408,000 $ 8,546,000 Net operating loss carryforwards 89,399,000 71,665,000 Research and development and other tax credits 9,432,000 7,531,000 Deferred revenue 985,000 297,000 Deferred rent 2,013,000 2,097,000 Stock-based compensation 3,408,000 3,091,000 Acquired intangibles 912,000 858,000 Other 2,693,000 1,906,000 116,250,000 95,991,000 Valuation allowance (115,007,000 ) (94,039,000 ) Total deferred tax assets 1,243,000 1,952,000 Deferred tax liabilities: Acquired intangibles (142,000 ) (124,000 ) Investment in affiliated entity (4,000 ) (422,000 ) Fixed assets (1,121,000 ) (1,430,000 ) Net deferred tax liabilities $ (24,000 ) $ (24,000 )
Schedule of operating loss and tax credit carryforward expirations	Based upon statute, federal and state losses and credits are expected to expire as follows (in millions): Expiration Date: Federal NOLs State NOLs Federal R&D State R&D 2019 $ 2.4 $ — $ — $ — 2020 1.6 — — — 2021 2.3 0.3 — — 2022 6.0 0.3 — — 2023 4.5 0.4 — — 2024 and thereafter 280.0 143.2 13.8 — Indefinite 86.5 — — 2.7 $ 383.3 $ 144.2 $ 13.8 $ 2.7
Schedule of unrecognized tax benefits rollforward	The following table summarizes the activity related to the Company's unrecognized tax benefits: Year ended December 31, 2018 2017 2016 Balance at beginning of the year $ 8,313,000 $ 6,855,000 $ 5,455,000 Increases related to current year tax positions 1,319,000 1,532,000 1,183,000 Increases (decreases) related to prior year tax positions — (74,000 ) 217,000 Balance at end of the year $ 9,632,000 $ 8,313,000 $ 6,855,000

Quarterly Financial Informati_2

Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
Quarterly Financial Information (Unaudited) (Tables)	Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Schedule of quarterly financial information (unaudited)	The following is a summary of the quarterly results of operations of the Company for the years ended December 31, 2018 and 2017 (unaudited): Quarter Ended Quarter Ended Quarter Ended Quarter Ended December 31, September 30, June 30, March 31, Consolidated Statements of Operations: Revenue: Revenue under collaborative research and development arrangements $ 2,372,600 $ 1,813,287 $ 24,385,852 $ 1,289,046 Revenue under collaborative research and development arrangements with affiliated entity 56,207 184,990 60,319 148,008 Grants and miscellaneous revenue 73,817 2,591 2,590 92,590 Total revenues 2,502,624 2,000,868 24,448,761 1,529,644 Operating Expenses: Research and development 26,365,647 21,851,858 22,462,620 24,577,751 General and administrative 5,636,141 6,791,693 7,189,310 9,698,015 Total operating expenses 32,001,788 28,643,551 29,651,930 34,275,766 Loss from operations (29,499,164 ) (26,642,683 ) (5,203,169 ) (32,746,122 ) Interest and other income, net (169,300 ) 380,987 396,681 312,523 Change in fair value of common stock warrants — 228,665 259,971 (127,841 ) Gain (loss) from investment in affiliated entity (3,293,741 ) 1,017,359 (2,092,608 ) 2,380,423 Net loss before provision for income taxes $ (32,962,205 ) $ (25,015,672 ) $ (6,639,125 ) $ (30,181,017 ) Provision for income taxes — — — (2,169,811 ) Net loss $ (32,962,205 ) $ (25,015,672 ) $ (6,639,125 ) $ (32,350,828 ) Net loss per share Basic $ (0.34 ) $ (0.27 ) $ (0.07 ) $ (0.36 ) Diluted $ (0.34 ) $ (0.27 ) $ (0.08 ) $ (0.36 ) Quarter Ended Quarter Ended Quarter Ended Quarter Ended December 31, September 30, June 30, March 31, Consolidated Statements of Operations: Revenue: Revenue under collaborative research and development arrangements $ 7,409,214 $ 351,272 $ 16,358,316 $ 4,288,586 Revenue under collaborative research and development arrangements with affiliated entity 226,486 129,133 176,879 233,330 Grants and miscellaneous revenue 980,443 1,456,216 2,797,647 5,240,233 Grants and miscellaneous revenue from affiliated entity 171,091 707,922 1,079,282 614,036 Total revenues 8,787,234 2,644,543 20,412,124 10,376,185 Operating Expenses: Research and development 24,641,124 25,510,239 23,878,751 24,542,504 General and administrative 8,033,899 6,319,775 6,169,106 7,767,589 Gain on sale of assets (1,000,000 ) — — — Total operating expenses 31,675,023 31,830,014 30,047,857 32,310,093 Loss from operations (22,887,789 ) (29,185,471 ) (9,635,733 ) (21,933,908 ) Interest and other income, net 509,266 463,346 300,021 340,341 Change in fair value of common stock warrants 579,546 423,296 (312,500 ) 116,477 Gain (loss) from investment in affiliated entity 292,798 (5,835,741 ) 169,096 (1,608,817 ) Net loss $ (21,506,179 ) $ (34,134,570 ) $ (9,479,116 ) $ (23,085,907 ) Net loss per share Basic $ (0.24 ) $ (0.39 ) $ (0.13 ) $ (0.31 ) Diluted $ (0.24 ) $ (0.40 ) $ (0.13 ) $ (0.31 )

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narrative (Details)	Mar. 01, 2019USD ($)	Mar. 12, 2019USD ($)	Dec. 31, 2018USD ($)segment	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jan. 01, 2018USD ($)	Jan. 01, 2017USD ($)
Property, Plant and Equipment [Line Items]
Net loss from operations			$ (96,967,830)	$ (88,205,772)	$ (73,740,339)
Working capital			52,500,000
Accumulated deficit			(620,426,436)	(523,356,317)		$ (523,124,951)
Cash, cash equivalents, and short-term investments			81,200,000
Long-term investments			9,400,000
Proceeds from issuance of common stock			$ 29,227,776	94,347,922	$ 6,295,761
Number of operating segments \| segment			1
Allowance for doubtful accounts			$ 0	0
Intangible assets, net			4,760,145	6,009,729
Deferred tax assets, valuation allowance			115,007,000	94,039,000
Cumulative effect of accounting change						0	$ 0
Grant proceeds received			$ 9,500,000
Minimum
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, useful life			3 years
Intangible asset, useful life			2 years
Maximum
Property, Plant and Equipment [Line Items]
Property, plant, and equipment, useful life			5 years
Intangible asset, useful life			18 years
Patents \| Minimum
Property, Plant and Equipment [Line Items]
Intangible asset, useful life			8 years
Patents \| Maximum
Property, Plant and Equipment [Line Items]
Intangible asset, useful life			17 years
Accounting Standards Update 2016-01
Property, Plant and Equipment [Line Items]
Accumulated deficit						231,366
Retained earnings
Property, Plant and Equipment [Line Items]
Cumulative effect of accounting change						231,366	(312,310)
Retained earnings \| Accounting Standards Update 2016-09
Property, Plant and Equipment [Line Items]
Cumulative effect of accounting change							(312,000)
Retained earnings \| Accounting Standards Update 2016-01
Property, Plant and Equipment [Line Items]
Cumulative effect of accounting change						(231,000)
Additional paid-in capital
Property, Plant and Equipment [Line Items]
Cumulative effect of accounting change							312,310
Additional paid-in capital \| Accounting Standards Update 2016-09
Property, Plant and Equipment [Line Items]
Cumulative effect of accounting change							$ 312,000
Accumulated other comprehensive income (loss)
Property, Plant and Equipment [Line Items]
Cumulative effect of accounting change						(231,366)
Accumulated other comprehensive income (loss) \| Accounting Standards Update 2016-01
Property, Plant and Equipment [Line Items]
Cumulative effect of accounting change						$ (231,000)
Common stock \| Sales Agreement
Property, Plant and Equipment [Line Items]
Stock sales agreement, remaining authorized sales amount			$ 71,800,000
Proceeds from issuance of common stock			29,200,000
Common stock \| Underwritten Public Offering And Sales Agreement
Property, Plant and Equipment [Line Items]
Proceeds from issuance of common stock				$ 94,300,000
Plumbline Life Sciences
Property, Plant and Equipment [Line Items]
Equity securities, FV-NI, gain (loss)			$ 699,000
Convertible Debt \| 6.50% Convertible Senior Notes Due 2024
Property, Plant and Equipment [Line Items]
Stated interest rate			6.50%
Convertible Debt \| Subsequent Event \| 6.50% Convertible Senior Notes Due 2024
Property, Plant and Equipment [Line Items]
Proceeds from issuance of debt	$ 75,800,000	$ 75,800,000
Debt instrument, face amount	$ 78,500,000	$ 78,500,000
VGX Animal Health, Inc
Property, Plant and Equipment [Line Items]
Non-controlling interest			15.00%

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Calculation of Net Loss Per Share (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Numerator
Net loss (numerator for use in basic net loss per share)									$ (96,967,830)	$ (88,205,772)	$ (73,740,339)
Adjustment for decrease in fair value of warrant liability									0	(806,819)	0
Numerator for use in diluted net loss per share									$ (96,967,830)	$ (89,012,591)	$ (73,740,339)
Denominator
Weighted average number of common shares outstanding (denominator for use in basic net loss per share) (shares)									92,539,997	81,777,493	73,214,766
Effect of dilutive potential common shares (shares)									0	140,529	0
Denominator for use in diluted loss per share (shares)									92,539,997	81,918,022	73,214,766
Net loss per share, diluted ($ per share)	$ (0.34)	$ (0.27)	$ (0.08)	$ (0.36)	$ (0.24)	$ (0.40)	$ (0.13)	$ (0.31)	$ (1.05)	$ (1.09)	$ (1.01)
Net loss per share, basic ($ per share)	$ (0.34)	$ (0.27)	$ (0.07)	$ (0.36)	$ (0.24)	$ (0.39)	$ (0.13)	$ (0.31)	$ (1.05)	$ (1.08)	$ (1.01)

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Antidilutive Securities Table (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of common shares that were excluded from the diluted net loss per share calculation because of their anti-dilutive effect
Total antidilutive securities (shares)	10,449,150	8,937,494	7,897,564
Options to purchase common stock
Summary of common shares that were excluded from the diluted net loss per share calculation because of their anti-dilutive effect
Total antidilutive securities (shares)	8,752,677	7,694,870	6,806,183
Warrants to purchase common stock
Summary of common shares that were excluded from the diluted net loss per share calculation because of their anti-dilutive effect
Total antidilutive securities (shares)	0	0	284,091
Restricted stock units
Summary of common shares that were excluded from the diluted net loss per share calculation because of their anti-dilutive effect
Total antidilutive securities (shares)	1,688,017	1,234,168	798,834
Convertible preferred stock
Summary of common shares that were excluded from the diluted net loss per share calculation because of their anti-dilutive effect
Total antidilutive securities (shares)	8,456	8,456	8,456

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Summary of Stock-Based Compensation Assumptions (Details) - Stock Options	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employees and Directors
Summary of assumptions used to estimate the fair value of stock options
Risk-free interest rate	2.73%	2.20%	0.91%
Expected volatility	72.00%	73.00%	76.00%
Expected life in years	6 years	6 years	5 years
Dividend yield	0.00%	0.00%	0.00%
Forfeiture rate			7.00%
Non Employee
Summary of assumptions used to estimate the fair value of stock options
Risk-free interest rate (minimum)	2.60%	2.40%	2.30%
Risk-free interest rate (maximum)	3.00%	2.60%	2.50%
Dividend yield	0.00%	0.00%	0.00%
Non Employee \| Minimum
Summary of assumptions used to estimate the fair value of stock options
Expected volatility	68.00%	97.00%	71.00%
Expected life in years	9 years	9 years	7 years
Non Employee \| Maximum
Summary of assumptions used to estimate the fair value of stock options
Expected volatility	101.00%	102.00%	104.00%
Expected life in years	10 years	10 years	10 years

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Impact of Adoption of ASU 2014-09 (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues:
Total revenues	$ 2,502,624	$ 2,000,868	$ 24,448,761	$ 1,529,644	$ 8,787,234	$ 2,644,543	$ 20,412,124	$ 10,376,185	$ 30,481,897	$ 42,220,086	$ 35,368,361
Operating expenses:
Research and development	26,365,647	21,851,858	22,462,620	24,577,751	24,641,124	25,510,239	23,878,751	24,542,504	95,257,876	98,572,618	88,712,035
General and administrative	5,636,141	6,791,693	7,189,310	9,698,015	8,033,899	6,319,775	6,169,106	7,767,589	29,315,159	28,290,369	23,892,263
Total operating expenses	32,001,788	28,643,551	29,651,930	34,275,766	31,675,023	31,830,014	30,047,857	32,310,093	124,573,035	125,862,987	111,604,298
Calculated under Revenue Guidance in Effect before Topic 606
Revenues:
Total revenues									39,973,602
Operating expenses:
Research and development									104,749,581
General and administrative									29,315,159
Total operating expenses									134,064,740
Revenue under collaborative research and development arrangements
Revenues:
Total revenues	2,372,600	1,813,287	24,385,852	1,289,046	7,409,214	351,272	16,358,316	4,288,586	29,860,785	28,407,388	6,490,747
Revenue under collaborative research and development arrangements \| Calculated under Revenue Guidance in Effect before Topic 606
Revenues:
Total revenues									29,860,785
Revenue under collaborative research and development arrangements with affiliated entity
Revenues:
Total revenues	56,207	184,990	60,319	148,008	226,486	129,133	176,879	233,330	449,524	765,828	1,400,594
Revenue under collaborative research and development arrangements with affiliated entity \| Calculated under Revenue Guidance in Effect before Topic 606
Revenues:
Total revenues									449,524
Grants and miscellaneous revenue
Revenues:
Total revenues	$ 73,817	$ 2,591	$ 2,590	$ 92,590	980,443	1,456,216	2,797,647	5,240,233	171,588	10,474,539	27,136,457
Grants and miscellaneous revenue \| Calculated under Revenue Guidance in Effect before Topic 606
Revenues:
Total revenues									6,315,116
Grants and miscellaneous revenue from affiliated entity
Revenues:
Total revenues					$ 171,091	$ 707,922	$ 1,079,282	$ 614,036	0	$ 2,572,331	$ 340,563
Grants and miscellaneous revenue from affiliated entity \| Calculated under Revenue Guidance in Effect before Topic 606
Revenues:
Total revenues									3,348,177
Accounting Standards Update 2014-09 \| Difference between Revenue Guidance in Effect before and after Topic 606
Revenues:
Total revenues									(9,491,705)
Operating expenses:
Research and development									(9,491,705)
General and administrative									0
Total operating expenses									(9,491,705)
Accounting Standards Update 2014-09 \| Revenue under collaborative research and development arrangements \| Difference between Revenue Guidance in Effect before and after Topic 606
Revenues:
Total revenues									0
Accounting Standards Update 2014-09 \| Revenue under collaborative research and development arrangements with affiliated entity \| Difference between Revenue Guidance in Effect before and after Topic 606
Revenues:
Total revenues									0
Accounting Standards Update 2014-09 \| Grants and miscellaneous revenue \| Difference between Revenue Guidance in Effect before and after Topic 606
Revenues:
Total revenues									(6,143,528)
Accounting Standards Update 2014-09 \| Grants and miscellaneous revenue from affiliated entity \| Difference between Revenue Guidance in Effect before and after Topic 606
Revenues:
Total revenues									$ (3,348,177)

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Impact of Adoption of ASU 2016-01 (Details) - USD ($)	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit	$ (620,426,436)	$ (523,124,951)	$ (523,356,317)
Accumulated other comprehensive loss	$ (528,867)	(348,371)	$ (117,005)
Accounting Standards Update 2016-01
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accumulated deficit		231,366
Accumulated other comprehensive loss		$ (231,366)

Revenue Recognition - Narrative

Revenue Recognition - Narrative (Details) - USD ($)	3 Months Ended								12 Months Ended
Revenue Recognition - Narrative (Details) - USD ($)	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total revenues	$ 2,502,624	$ 2,000,868	$ 24,448,761	$ 1,529,644	$ 8,787,234	$ 2,644,543	$ 20,412,124	$ 10,376,185	$ 30,481,897	$ 42,220,086	$ 35,368,361
Revenue recognized from deferred revenue beginning balance									1,300,000	14,800,000
ApolloBio
Disaggregation of Revenue [Line Items]
Total revenues									23,000,000
AstraZeneca
Disaggregation of Revenue [Line Items]
Total revenues									6,900,000
Other Counterparty
Disaggregation of Revenue [Line Items]
Total revenues									117,000
GeneOne (affiliated entity)
Disaggregation of Revenue [Line Items]
Revenue from Related Parties									$ 342,000	$ 551,000	$ 1,200,000

Collaborative Agreements (Detai

Collaborative Agreements (Details)	Apr. 11, 2018USD ($)	Dec. 29, 2017	Aug. 07, 2015product	Dec. 31, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Feb. 28, 2017USD ($)	Sep. 30, 2015USD ($)	Apr. 30, 2015USD ($)	Sep. 30, 2013USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues											$ 2,502,624	$ 2,000,868	$ 24,448,761	$ 1,529,644	$ 8,787,234	$ 2,644,543	$ 20,412,124	$ 10,376,185		$ 30,481,897	$ 42,220,086	$ 35,368,361
Revenue recognized from deferred revenue beginning balance																				1,300,000	14,800,000
Deferred grant funding				$ 4,165,848		$ 0					4,165,848				0					4,165,848	0
ApolloBio
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues																				23,000,000
ApolloBio \| Collaborative Arrangement, Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Territory expansion option period		3 years
Proceeds from collaborative agreement					$ 19,400,000
Upfront payment received					23,000,000															$ 23,000,000
Collaborative agreement, advisory fees					960,000									$ 960,000
Additional revenue to be achieved																			$ 20,000,000
Obligation period to pay royalties																				10 years
Collaborative agreement, period from effective date for termination																				1 year
Collaborative agreement, number of days written notice before termination																				90 days
AstraZeneca
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Revenues																				$ 6,900,000
Revenues																					22,300,000
AstraZeneca \| Collaborative Arrangement, Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received								$ 27,500,000													27,500,000
Collaboration agreement, anticipated development and regulatory event based payment receivable milestones																				355,000,000
Collaboration agreement, anticipated commercial event based payment receivable milestones																				345,000,000
Number of additional products \| product			2
Collaborative agreement, milestone payment, revenue recognized				2,000,000		7,000,000
Deferred revenue				288,000		1,100,000					288,000				1,100,000					288,000	1,100,000
Accounts receivable				3,200,000		1,700,000					3,200,000				1,700,000					3,200,000	1,700,000
Roche \| Collaborative Arrangement, Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received										$ 10,000,000
Full payment							$ 8,500,000
Revenue recognized from deferred revenue beginning balance																				0
Revenue under collaborative research and development arrangements																					6,100,000
Coalition for Epidemic Preparedness Innovations \| Collaborative Arrangement, Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Upfront payment received																				6,500,000
Collaborative agreement, funding to be received	$ 56,000,000
Collaborative agreement, period to receive funding for research and development	5 years
Collaborative agreement, funding received																				4,300,000
Deferred grant funding				2,100,000							2,100,000									2,100,000
DARPA \| Collaborative Arrangement, Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Deferred revenue				74,000		149,000					74,000				149,000					74,000	149,000
Accounts receivable				$ 82,000		$ 4,100,000					$ 82,000				$ 4,100,000					82,000	4,100,000
Collaborative agreement, funding received																				$ 1,100,000	$ 9,800,000
Base award									$ 19,600,000
Option award									$ 24,600,000
Foreign Tax Authority \| ApolloBio \| Collaborative Arrangement, Product
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Collaborative agreement, corporate income tax					2,200,000
Collaborative agreement, foreign non-income Taxes					$ 1,400,000

Investments - Narrative (Detail

Investments - Narrative (Details)	12 Months Ended
Investments - Narrative (Details)	Dec. 31, 2018USD ($)investment	Dec. 31, 2017USD ($)
Investments, Debt and Equity Securities [Abstract]
Other-than-temporary impairment loss, debt securities, portion recognized in earnings	$ 1,300,000	$ 215,000
Other than temporary impairments	$ 0	$ 0
Number of securities in a gross unrealized loss position \| investment	14
Number of securities in a gross unrealized loss position for more than twelve months \| investment	10
Unrealized loss	$ 193,000

Investments - Summary of Availa

Investments - Summary of Available-for-sale Securities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Jun. 30, 2015
Debt Securities, Available-for-sale [Line Items]
Cost	$ 58,067,588
Gross Unrealized Gains	0
Gross Unrealized Losses	(528,736)
Fair Market Value	57,538,852
Cost			$ 0
Cost		$ 103,986,286
Gross Unrealized Gains		2,370,208
Gross Unrealized Losses		(392,571)
Fair Market Value		105,963,923
Mutual funds
Debt Securities, Available-for-sale [Line Items]
Cost	57,842,955	68,776,165
Gross Unrealized Gains	0	42,097
Gross Unrealized Losses	(528,084)	(252,373)
Fair Market Value	57,314,871	68,565,889
US corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Cost	224,633	35,210,121
Gross Unrealized Gains	0	3,032
Gross Unrealized Losses	(652)	(140,198)
Fair Market Value	$ 223,981	35,072,955
Common stock
Debt Securities, Available-for-sale [Line Items]
Cost		0
Gross Unrealized Gains		2,325,079
Gross Unrealized Losses		0
Fair Market Value		$ 2,325,079
Maximum \| US corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Contractual maturity	2 years	2 years

Marketable Securities and Fai_3

Marketable Securities and Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Financial assets and liabilities that are measured at fair value on recurring basis
Long-term investments	$ 9,400,000
Investments in affiliated entities
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	9,405,913
Fair Value, Measurements, Recurring
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	76,591,272	$ 124,876,806
Liabilities, fair value		360,795
Fair Value, Measurements, Recurring \| Quoted Prices in Active Markets (Level 1)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	19,052,420	21,237,962
Liabilities, fair value		0
Fair Value, Measurements, Recurring \| Significant Other Unobservable Inputs (Level 2)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	57,538,852	103,638,844
Liabilities, fair value		0
Fair Value, Measurements, Recurring \| Significant Unobservable Inputs (Level 3)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	0	0
Liabilities, fair value		360,795
Fair Value, Measurements, Recurring \| Money market funds
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	9,646,507	9,843,482
Fair Value, Measurements, Recurring \| Money market funds \| Quoted Prices in Active Markets (Level 1)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	9,646,507	9,843,482
Fair Value, Measurements, Recurring \| Money market funds \| Significant Other Unobservable Inputs (Level 2)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	0	0
Fair Value, Measurements, Recurring \| Money market funds \| Significant Unobservable Inputs (Level 3)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	0	0
Fair Value, Measurements, Recurring \| Mutual funds
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	57,314,871	68,565,889
Fair Value, Measurements, Recurring \| Mutual funds \| Quoted Prices in Active Markets (Level 1)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	0	0
Fair Value, Measurements, Recurring \| Mutual funds \| Significant Other Unobservable Inputs (Level 2)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	57,314,871	68,565,889
Fair Value, Measurements, Recurring \| Mutual funds \| Significant Unobservable Inputs (Level 3)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	0	0
Fair Value, Measurements, Recurring \| US corporate debt securities
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	223,981	35,072,955
Fair Value, Measurements, Recurring \| US corporate debt securities \| Quoted Prices in Active Markets (Level 1)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	0	0
Fair Value, Measurements, Recurring \| US corporate debt securities \| Significant Other Unobservable Inputs (Level 2)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	223,981	35,072,955
Fair Value, Measurements, Recurring \| US corporate debt securities \| Significant Unobservable Inputs (Level 3)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	0	0
Fair Value, Measurements, Recurring \| Investments in affiliated entities
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value		11,394,480
Fair Value, Measurements, Recurring \| Investments in affiliated entities \| Quoted Prices in Active Markets (Level 1)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value		11,394,480
Fair Value, Measurements, Recurring \| Investments in affiliated entities \| Significant Other Unobservable Inputs (Level 2)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	0	0
Fair Value, Measurements, Recurring \| Investments in affiliated entities \| Significant Unobservable Inputs (Level 3)
Financial assets and liabilities that are measured at fair value on recurring basis
Assets, fair value	$ 0	0
Fair Value, Measurements, Recurring \| Common stock warrants
Financial assets and liabilities that are measured at fair value on recurring basis
Liabilities, fair value		360,795
Fair Value, Measurements, Recurring \| Common stock warrants \| Quoted Prices in Active Markets (Level 1)
Financial assets and liabilities that are measured at fair value on recurring basis
Liabilities, fair value		0
Fair Value, Measurements, Recurring \| Common stock warrants \| Significant Other Unobservable Inputs (Level 2)
Financial assets and liabilities that are measured at fair value on recurring basis
Liabilities, fair value		0
Fair Value, Measurements, Recurring \| Common stock warrants \| Significant Unobservable Inputs (Level 3)
Financial assets and liabilities that are measured at fair value on recurring basis
Liabilities, fair value		$ 360,795

Marketable Securities and Fai_4

Marketable Securities and Fair Value Measurements - Narrative (Details) - USD ($)	3 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jun. 30, 2015
Marketable Securities and Fair Value Measurements (Textual) [Abstract]
Carryover basis					$ 0
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Exercised	284,091		0
Common stock warrants		$ 0	$ 360,795
Proceeds from warrant exercises	$ 902,000	902,000
Increase (decrease) in the fair value		$ (361,000)	$ (807,000)	$ (134,000)
Fair Value, Inputs, Level 1
Marketable Securities and Fair Value Measurements (Textual) [Abstract]
Investments in and Advances to Affiliates, Balance, Shares		1,644,155
Common stock \| Fair Value, Inputs, Level 1
Marketable Securities and Fair Value Measurements (Textual) [Abstract]
Number of shares owned (shares)		395,758

Marketable Securities and Fai_5

Marketable Securities and Fair Value Measurements - Assumptions Used to Estimate Fair Value of Common Stock Warrants (Details)	Dec. 31, 2017year$ / shares
Risk-free interest rate
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.0175
Expected volatility
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input	0.55
Expected life in years
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input \| year	0.70
Dividend yield
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warrants and Rights Outstanding, Measurement Input \| $ / shares	0

Marketable Securities and Fai_6

Marketable Securities and Fair Value Measurements - Changes in Fair Value of Level 3 Financial Liabilities (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Changes in fair value of the financial liabilities
Decrease in fair value included in change in fair value of common stock warrants	$ (361,000)	$ (807,000)	$ (134,000)
Significant Unobservable Inputs (Level 3)
Changes in fair value of the financial liabilities
Balance at beginning of year	360,795	1,167,614
Decrease in fair value included in change in fair value of common stock warrants	(360,795)	(806,819)
Balance at end of year	$ 0	$ 360,795	$ 1,167,614

Major Customers and Concentra_3

Major Customers and Concentration of Credit Risk (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Concentration Risk [Line Items]
Total revenues	$ 2,502,624	$ 2,000,868	$ 24,448,761	$ 1,529,644	$ 8,787,234	$ 2,644,543	$ 20,412,124	$ 10,376,185	$ 30,481,897	$ 42,220,086	$ 35,368,361
Revenue \| Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage									100.00%	100.00%	100.00%
ApolloBio
Concentration Risk [Line Items]
Total revenues									$ 23,000,000	$ 0	$ 0
ApolloBio \| Revenue \| Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage									75.00%	0.00%	0.00%
AstraZeneca
Concentration Risk [Line Items]
Total revenues									$ 6,850,424	$ 22,269,773	$ 1,518,639
Accounts receivable	$ 3,200,000								$ 3,200,000		$ 1,700,000
AstraZeneca \| Revenue \| Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage									23.00%	53.00%	4.00%
AstraZeneca \| Accounts Receivable \| Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage									98.00%		28.00%
DARPA
Concentration Risk [Line Items]
Total revenues									$ 0	$ 9,983,927	$ 26,602,183
Accounts receivable					$ 4,100,000					$ 4,100,000
DARPA \| Revenue \| Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage									0.00%	24.00%	75.00%
DARPA \| Accounts Receivable \| Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage										69.00%
Roche
Concentration Risk [Line Items]
Total revenues									$ 0	$ 6,107,254	$ 4,917,929
Roche \| Revenue \| Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage									0.00%	14.00%	14.00%
GeneOne (affiliated entity)
Concentration Risk [Line Items]
Total revenues									$ 342,386	$ 551,208	$ 1,188,432
GeneOne (affiliated entity) \| Revenue \| Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage									1.00%	1.00%	4.00%
All other
Concentration Risk [Line Items]
Total revenues									$ 289,087	$ 3,307,924	$ 1,141,178
All other \| Revenue \| Customer Concentration Risk
Concentration Risk [Line Items]
Concentration risk, percentage									1.00%	8.00%	3.00%

Fixed Assets (Details)

Fixed Assets (Details) - USD ($)	12 Months Ended
Fixed Assets (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Cost	$ 25,948,933	$ 25,426,733
Accumulated Depreciation and Amortization	(9,999,919)	(7,106,557)
Net Book Value	15,949,014	18,320,176
Depreciation	3,747,183	1,850,376	$ 1,708,498
Leasehold improvements
Property, Plant and Equipment [Line Items]
Cost	14,909,341	14,553,993
Accumulated Depreciation and Amortization	(3,464,444)	(2,042,871)
Net Book Value	11,444,897	12,511,122
Laboratory equipment
Property, Plant and Equipment [Line Items]
Cost	4,031,965	3,787,578
Accumulated Depreciation and Amortization	(2,425,854)	(1,724,946)
Net Book Value	1,606,111	2,062,632
Office furniture and fixtures
Property, Plant and Equipment [Line Items]
Cost	3,198,803	3,366,896
Accumulated Depreciation and Amortization	(1,767,653)	(1,471,705)
Net Book Value	1,431,150	1,895,191
Computer equipment and other
Property, Plant and Equipment [Line Items]
Cost	3,808,824	3,718,266
Accumulated Depreciation and Amortization	(2,341,968)	(1,867,035)
Net Book Value	$ 1,466,856	$ 1,851,231

Goodwill and Intangible Asset_2

Goodwill and Intangible Assets - Summary of Goodwill and Intangible Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Apr. 30, 2016	Jun. 30, 2009	Jan. 31, 2005
Indefinite lived:
Goodwill, Gross	$ 10,513,371	$ 10,513,371
Goodwill	10,513,371	10,513,371
Definite lived:
Intangible assets, Gross	24,717,873	24,717,873
Intangible assets, Accumulated Amortization	(19,957,728)	(18,708,144)
Intangible assets, net book value	4,760,145	6,009,729
Total goodwill and intangible assets, Gross	35,231,244	35,231,244
Total goodwill and intangible assets, Net Book Value	$ 15,273,516	16,523,100
Inovio AS
Indefinite lived:
Goodwill					$ 3,900,000
VGX
Indefinite lived:
Goodwill				$ 6,200,000
Bioject
Indefinite lived:
Goodwill			$ 400,000
Minimum
Schedule of intangible assets by major asset class
Intangible asset, useful life	2 years
Maximum
Schedule of intangible assets by major asset class
Intangible asset, useful life	18 years
Patents
Definite lived:
Intangible assets, Gross	$ 5,802,528	5,802,528
Intangible assets, Accumulated Amortization	(5,742,079)	(5,681,673)
Intangible assets, net book value	$ 60,449	120,855
Patents \| Minimum
Schedule of intangible assets by major asset class
Intangible asset, useful life	8 years
Patents \| Maximum
Schedule of intangible assets by major asset class
Intangible asset, useful life	17 years
Licenses
Definite lived:
Intangible assets, Gross	$ 1,323,761	1,323,761
Intangible assets, Accumulated Amortization	(1,219,357)	(1,190,609)
Intangible assets, net book value	$ 104,404	133,152
Licenses \| Minimum
Schedule of intangible assets by major asset class
Intangible asset, useful life	8 years
Licenses \| Maximum
Schedule of intangible assets by major asset class
Intangible asset, useful life	17 years
CELLECTRA
Definite lived:
Intangible assets, Gross	$ 8,106,270	8,106,270
Intangible assets, Accumulated Amortization	(7,679,190)	(7,252,108)
Intangible assets, net book value	$ 427,080	854,162
CELLECTRA \| Minimum
Schedule of intangible assets by major asset class
Intangible asset, useful life	5 years
CELLECTRA \| Maximum
Schedule of intangible assets by major asset class
Intangible asset, useful life	11 years
GHRH
Schedule of intangible assets by major asset class
Intangible asset, useful life	11 years
Definite lived:
Intangible assets, Gross	$ 335,314	335,314
Intangible assets, Accumulated Amortization	(303,630)	(271,948)
Intangible assets, net book value	31,684	63,366
Bioject
Definite lived:
Intangible assets, Gross	5,100,000	5,100,000
Intangible assets, Accumulated Amortization	(1,882,222)	(1,405,556)
Intangible assets, net book value	$ 3,217,778	3,694,444
Bioject \| Minimum
Schedule of intangible assets by major asset class
Intangible asset, useful life	2 years
Bioject \| Maximum
Schedule of intangible assets by major asset class
Intangible asset, useful life	15 years
Other
Schedule of intangible assets by major asset class
Intangible asset, useful life	18 years
Definite lived:
Intangible assets, Gross	$ 4,050,000	4,050,000
Intangible assets, Accumulated Amortization	(3,131,250)	(2,906,250)
Intangible assets, net book value	$ 918,750	$ 1,143,750

Goodwill and Intangible Asset_3

Goodwill and Intangible Assets - Schedule of Amortization Expense (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Goodwill and Intangible Assets (Textual) [Abstract]
2019	$ 1,066,251
2020	547,081
2021	520,414
2022	492,818
2023	275,803
Thereafter	1,857,778
Intangible assets, net book value	$ 4,760,145	$ 6,009,729

Goodwill and Intangible Asset_4

Goodwill and Intangible Assets - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of intangible assets	$ 1,249,584	$ 1,618,665	$ 1,377,466
Impairment	$ 0	$ 0	$ 0

Accounts Payable and Accrued _3

Accounts Payable and Accrued Expenses (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Payables and Accruals [Abstract]
Trade accounts payable	$ 10,043,816	$ 7,564,830
Accrued compensation	9,466,821	7,997,152
Accrued subcontract costs	83,812	3,746,937
Other accrued expenses	3,540,284	3,969,879
Accounts payable and accrued liabilities	$ 23,134,733	$ 23,278,798

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Preferred Stock (Details) - $ / shares	Dec. 31, 2018	Dec. 31, 2017
Summary of common and preferred stock authorized, issued and outstanding
Preferred Stock, par value ($ per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized (shares)	10,000,000	10,000,000
Preferred stock, shares issued (shares)	23	23
Preferred stock, shares outstanding (shares)	23	23
Series C Preferred Stock
Summary of common and preferred stock authorized, issued and outstanding
Preferred Stock, par value ($ per share)	$ 0.001
Preferred stock, shares authorized (shares)	1,091
Preferred stock, shares issued (shares)	1,091
Preferred stock, shares outstanding (shares)	23	23

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Warrants Outstanding (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Summary of warrants outstanding
Number of warrants (shares)	0	284,091
Common Stock Warrant Liability	$ 0	$ 360,795
March 2013 financing
Summary of warrants outstanding
Exercise price ($ per share)	$ 3.17
Expiration Date	Sep. 12, 2018
Number of warrants (shares)	0	284,091
Common Stock Warrant Liability	$ 0	$ 360,795

Stockholders' Equity - Summar_3

Stockholders' Equity - Summary of Stock Options Outstanding (Details)	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options outstanding (shares) \| shares	8,752,677
Weighted-Average Remaining Contractual Life (in Years)	6 years 7 months 31 days
Weighted average exercise price ($ per share)	$ 6.35
Options exercisable (shares) \| shares	6,154,495
Weighted-average exercise price ($ per share)	$ 6.78
$1.48-$3.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price, lower range limit	1.48
Exercise price, upper range limit	$ 3
Options outstanding (shares) \| shares	879,321
Weighted-Average Remaining Contractual Life (in Years)	3 years 7 months 31 days
Weighted average exercise price ($ per share)	$ 2.26
Options exercisable (shares) \| shares	879,321
Weighted-average exercise price ($ per share)	$ 2.26
$3.01-$6.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price, lower range limit	3.01
Exercise price, upper range limit	$ 6
Options outstanding (shares) \| shares	2,558,453
Weighted-Average Remaining Contractual Life (in Years)	7 years 10 months 30 days
Weighted average exercise price ($ per share)	$ 4.38
Options exercisable (shares) \| shares	974,723
Weighted-average exercise price ($ per share)	$ 4.44
$6.01-$9.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price, lower range limit	6.01
Exercise price, upper range limit	$ 9
Options outstanding (shares) \| shares	4,394,357
Weighted-Average Remaining Contractual Life (in Years)	6 years 7 months 31 days
Weighted average exercise price ($ per share)	$ 7.11
Options exercisable (shares) \| shares	3,408,953
Weighted-average exercise price ($ per share)	$ 7.20
$9.01-$12.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price, lower range limit	9.01
Exercise price, upper range limit	$ 12
Options outstanding (shares) \| shares	257,836
Weighted-Average Remaining Contractual Life (in Years)	6 years 10 months 30 days
Weighted average exercise price ($ per share)	$ 9.79
Options exercisable (shares) \| shares	228,788
Weighted-average exercise price ($ per share)	$ 9.81
$12.01-$15.00
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price, lower range limit	12.01
Exercise price, upper range limit	$ 15
Options outstanding (shares) \| shares	662,710
Weighted-Average Remaining Contractual Life (in Years)	5 years 2 months 28 days
Weighted average exercise price ($ per share)	$ 12.96
Options exercisable (shares) \| shares	662,710
Weighted-average exercise price ($ per share)	$ 12.96

Stockholders' Equity - Summar_4

Stockholders' Equity - Summary of Stock Option Activity Under Equity Incentive Plan (Details)	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Number of Shares
Beginning Balance (shares) \| shares	7,694,870
Granted (shares) \| shares	2,176,935
Exercised (shares) \| shares	(472,762)
Cancelled (shares) \| shares	(646,366)
Ending Balance (shares) \| shares	8,752,677
Weighted-Average Exercise Price
Beginning Balance ($ per share) \| $ / shares	$ 6.77
Granted ($ per share) \| $ / shares	4.32
Exercised ($ per share) \| $ / shares	3.21
Cancelled ($ per share) \| $ / shares	6.83
Ending Balance ($ per share) \| $ / shares	$ 6.35

Stockholders' Equity - Summar_5

Stockholders' Equity - Summary of RSU Activity Under Equity Incentive Plan (Details) - Restricted stock units	12 Months Ended
	Dec. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Beginning balance (shares) \| shares	1,234,168
Granted (shares) \| shares	1,070,106
Vested (shares) \| shares	(539,468)
Cancelled (shares) \| shares	(76,789)
Ending balance (shares) \| shares	1,688,017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Beginning balance ($ per share) \| $ / shares	$ 0
Granted ($ per share) \| $ / shares	0
Vested ($ per share) \| $ / shares	0
Cancelled ($ per share) \| $ / shares	0
Ending balance ($ per share) \| $ / shares	$ 0

Stockholders' Equity - Narrativ

Stockholders' Equity - Narrative (Details)	Jul. 25, 2017USD ($)$ / sharesshares	May 31, 2018USD ($)	Sep. 30, 2018USD ($)	Jun. 05, 2018USD ($)$ / sharesshares	Dec. 31, 2018USD ($)dayvote$ / sharesshares	Dec. 31, 2017USD ($)$ / sharesshares	Dec. 31, 2016USD ($)$ / sharesshares	Jun. 05, 2018USD ($)$ / sharesshares	Jan. 01, 2018shares	May 13, 2016shares
Class of Stock [Line Items]
Preferred stock, par value ($ per share) \| $ / shares					$ 0.001	$ 0.001
Convertible preferred stock, shares issued upon conversion, conversion price ($ per share) \| $ / shares					27.20
Daily market price triggering mandatory conversion ($ per share) \| $ / shares					$ 72
Number of trading days \| day					20
Number of consecutive trading days \| day					30
Proceeds from issuance of common stock					$ 29,227,776	$ 94,347,922	$ 6,295,761
Warrants exercised in period (shares) \| shares					284,091	0
Proceeds from warrant exercises			$ 902,000		$ 902,000
Number of warrants (shares) \| shares					0	284,091
Share-based compensation					$ 10,654,622	$ 13,070,962	$ 10,479,135
Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized					$ 5,200,000	$ 5,900,000
Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized, period for recognition					1 year 7 months 31 days	1 year 9 months 15 days
Number of options outstanding to purchase common stock (shares) \| shares					8,752,677	7,694,870
Aggregate intrinsic value of options outstanding					$ 1,600,000
Aggregate intrinsic value for options exercisable					$ 1,600,000
Options exercisable, remaining contractual term					5 years 9 months
Number of options expected to vest (shares) \| shares					8,752,677
Options, expirations in period, weighted average exercise price ($ per share) \| $ / shares					$ 5.17	$ 9.67	$ 9.01
Options, expirations in period \| shares					119,091	200,501	69,570
Options, grants in period, weighted average grant date fair value ($ per share) \| $ / shares					$ 2.86	$ 4.33	$ 4.59
Proceeds from stock options exercised					$ 1,500,000	$ 2,300,000	$ 1,800,000
Options, exercises in period, aggregate intrinsic value					910,000	519,000	3,500,000
Employee
Class of Stock [Line Items]
Share-based compensation					10,200,000	12,900,000	10,200,000
Research and Development Expense
Class of Stock [Line Items]
Share-based compensation					5,900,000	5,800,000	4,800,000
General and Administrative Expense
Class of Stock [Line Items]
Share-based compensation					4,300,000	7,100,000	5,400,000
Non Employee
Class of Stock [Line Items]
Allocated share-based compensation expense					$ 302,000	201,000	$ 321,000
Number of options outstanding to purchase common stock (shares) \| shares					628,125
Restricted Stock Units (RSUs)
Class of Stock [Line Items]
Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized					$ 5,100,000	$ 5,300,000
Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized, period for recognition					1 year 7 months 31 days	1 year 9 months
Aggregate intrinsic value of unvested					$ 6,800,000
Aggregate intrinsic value of vested					$ 2,400,000
RSU's expected to vest (shares) \| shares					1,688,017
Weighted average grant date fair value ($ per share) \| $ / shares					$ 4.31	$ 6.66	$ 7.41
Minimum
Class of Stock [Line Items]
Average daily trading volume triggering mandatory conversion (shares) \| shares					6,250
Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock, redemption price ($ per share) \| $ / shares					$ 10,000
Preferred stock, par value ($ per share) \| $ / shares					$ 0.001
Number of votes per share \| vote					368
Convertible preferred stock, shares issued upon conversion (shares) \| shares					8,456
Notice period for mandatory conversion of preferred stock					30 days
Common stock \| Sales Agreement
Class of Stock [Line Items]
Authorized amount		$ 100,000,000
Agent fee		3.00%
Stock sale agreement, aggregate number of shares issued (shares) \| shares					5,354,075
Sale of stock, price per share ($ per share) \| $ / shares					$ 5.27
Stock sale agreement, aggregate proceeds from issuance of stock					$ 27,700,000
Stock sales agreement, remaining authorized sales amount					71,800,000
Proceeds from issuance of common stock					$ 29,200,000
Common stock \| ATM Sales Agreement
Class of Stock [Line Items]
Stock sale agreement, aggregate number of shares issued (shares) \| shares				314,950		2,937,406		3,911,104
Sale of stock, price per share ($ per share) \| $ / shares				$ 5.07		$ 8.41		$ 5.07
Stock sale agreement, aggregate proceeds from issuance of stock				$ 1,600,000		$ 24,200,000		$ 32,100,000
Common stock \| Public Offering, Not IPO
Class of Stock [Line Items]
Sale of stock, price per share ($ per share) \| $ / shares	$ 6
Sale of stock, number of shares issued in transaction (shares) \| shares	12,500,000
Proceeds from issuance of common stock	$ 70,100,000
2016 Incentive Plan
Class of Stock [Line Items]
Reserved number of shares under the Incentive Plan (shares) \| shares					8,000,000					6,000,000
Number of potential shares authorized for issuance under a share-based compensation plan (shares) \| shares										2,000,000
Increase in number of shares authorized (shares) \| shares									2,000,000
Number of shares available for grants under the Incentive Plan (shares) \| shares					3,039,566
Number of shares of vested restricted stock outstanding under the plan (shares) \| shares					1,519,187
Number of common stock shares outstanding under the Incentive Plan (shares) \| shares					3,062,183
Vesting period of Incentive Plan					3 years
Contractual year term of Incentive Plan					10 years
2007 Incentive Plan
Class of Stock [Line Items]
Number of shares of vested restricted stock outstanding under the plan (shares) \| shares					168,830
Number of common stock shares outstanding under the Incentive Plan (shares) \| shares					5,690,494
Vesting period of Incentive Plan					3 years
Contractual year term of Incentive Plan					10 years

Commitments - Narrative (Detail

Commitments - Narrative (Details) $ in Thousands	1 Months Ended					12 Months Ended
Commitments - Narrative (Details) $ in Thousands	Jun. 30, 2017USD ($)ft²	Oct. 31, 2016USD ($)ft²	Jun. 30, 2015ft²	Mar. 31, 2014USD ($)ft²	Apr. 30, 2013ft²	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Jun. 30, 2016ft²	Jan. 31, 2016USD ($)
Operating Leased Assets [Line Items]
Rent expense, net						$ 3,200	$ 2,400	$ 1,600
San Diego Office
Operating Leased Assets [Line Items]
Area (square feet) \| ft²			31,207		26,500
Term of contract					10 years
Optional term extension of contract					5 years
Annual percentage increase in base rent						3.00%
Tenant Improvements										$ 3,400
San Diego, California
Operating Leased Assets [Line Items]
Area (square feet) \| ft²		51,000
Term of contract		10 years
Annual percentage increase in base rent						3.00%
Tenant Improvements						$ 2,300
Security deposit		$ 95
Plymouth Meeting, Pennsylvania
Operating Leased Assets [Line Items]
Area (square feet) \| ft²	57,361			20,858					27,583
Term of contract				11 years 6 months
Optional term extension of contract				5 years
Annual percentage increase in base rent						2.00%
Tenant Improvements						$ 2,600
Security deposit	$ 75			$ 49

Commitments - Summary of Future

Commitments - Summary of Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
2019	$ 3,756
2020	3,891
2021	3,979
2022	4,052
2023	4,023
Thereafter	15,952
Total	$ 35,653

Investments in Affiliated Ent_2

Investments in Affiliated Entities (Details) - shares	Dec. 31, 2018	Dec. 31, 2017
GeneOne Life Sciences
Related Party Transaction [Line Items]
Number of shares owned (shares)	1,644,155
Percentage of ownership	7.80%	7.80%
GeneOne Life Sciences \| Common stock
Related Party Transaction [Line Items]
Number of shares owned (shares)	1,644,155	1,644,155
Plumbline Life Sciences
Related Party Transaction [Line Items]
Percentage of ownership	15.10%	16.40%
Plumbline Life Sciences \| Common stock
Related Party Transaction [Line Items]
Number of shares owned (shares)	395,758	395,758

Income Taxes - Summary of the P

Income Taxes - Summary of the Provision for Income Taxes (Details) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current:
Federal					$ 0	$ 0	$ 0
State					0	0	0
Current Foreign Tax Expense (Benefit)					2,170,000	0	0
Current income tax expense (benefit)					2,170,000	0	0
Deferred:
Federal					0	0
State					0	0	0
Deferred Foreign Income Tax Expense (Benefit)					0	0	0
Deferred income tax expense (benefit)					0	0	0
Income tax expense (benefit)	$ 0	$ 0	$ 0	$ 2,169,811	$ 2,169,811	$ 0	$ 0

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Income Taxes (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Income (benefit) taxes at statutory rates	$ (19,908,000)	$ (30,872,000)	$ (25,809,000)
State income tax, net of federal benefit	(4,000)	(4,000)	(4,000)
Foreign income taxes	2,170,000	0	0
Change in valuation allowance	20,898,000	(20,965,000)	29,678,000
Research and development tax credits	(3,170,000)	(3,456,000)	(3,117,000)
Fair value warrant	(76,000)	(282,000)	(47,000)
Stock compensation	1,094,000	2,332,000	113,000
Uncertain tax positions	1,268,000	846,000	1,367,000
Expired NOLs and credits	2,176,000	454,000	4,269,000
Limited NOLs and credits	(2,176,000)	(165,000)	(6,456,000)
Change in tax rates	0	50,019,000	(495,000)
Other	(102,000)	2,093,000	501,000
Income tax expense (benefit)	$ 2,170,000	$ 0	$ 0

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($)	3 Months Ended				12 Months Ended
Income Taxes - Narrative (Details) - USD ($)	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Provision for income taxes	$ 0	$ 0	$ 0	$ 2,169,811	$ 2,169,811	$ 0	$ 0
Tax benefits expired	11,200,000				11,200,000
Decrease in deferred tax assets					50,000,000
Decrease in valuation allowance					50,200,000
Provisional income tax benefit					200,000
Unrecognized tax benefits that would impact effective tax rate	8,300,000				8,300,000	$ 7,100,000	$ 5,700,000
Federal
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards that will expire due to IRC Section 382 limitations	383,300,000				383,300,000
Net operating loss carryforwards	86,500,000				86,500,000
State
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards	144,200,000				144,200,000
California
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards that will expire due to IRC Section 382 limitations	68,600,000				68,600,000
Pennsylvania
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards that will expire due to IRC Section 382 limitations	75,600,000				75,600,000
Research Tax Credit Carryforward \| Federal
Operating Loss Carryforwards [Line Items]
Tax credit carryforward amount	13,800,000				13,800,000
Research Tax Credit Carryforward \| State
Operating Loss Carryforwards [Line Items]
Tax credit carryforward amount	$ 2,700,000				$ 2,700,000

Income Taxes - Significant Comp

Income Taxes - Significant Components of Deferred Tax Assets and Liabilities (Details) - USD ($)	Dec. 31, 2018	Dec. 31, 2017
Deferred tax assets:
Capitalized research expense	$ 7,408,000	$ 8,546,000
Net operating loss carryforwards	89,399,000	71,665,000
Research and development and other tax credits	9,432,000	7,531,000
Deferred revenue	985,000	297,000
Deferred rent	2,013,000	2,097,000
Stock-based compensation	3,408,000	3,091,000
Acquired intangibles	912,000	858,000
Other	2,693,000	1,906,000
Deferred tax assets, gross	116,250,000	95,991,000
Valuation allowance	(115,007,000)	(94,039,000)
Total deferred tax assets	1,243,000	1,952,000
Deferred tax liabilities:
Acquired intangibles	(142,000)	(124,000)
Investment in affiliated entity	(4,000)	(422,000)
Fixed assets	(1,121,000)	(1,430,000)
Net deferred tax liabilities	$ (24,000)	$ (24,000)

Income Taxes - Expected Expirat

Income Taxes - Expected Expirations of Federal and State Losses and Credits (Details)	Dec. 31, 2018USD ($)
State
Expirations of Operating Loss Carryforwards, Components [Abstract]
2019	$ 0
2020	0
2021	300,000
2022	300,000
2023	400,000
2024 and thereafter	143,200,000
Indefinite	0
Total	144,200,000
Federal
Expirations of Operating Loss Carryforwards, Components [Abstract]
2019	2,400,000
2020	1,600,000
2021	2,300,000
2022	6,000,000
2023	4,500,000
2024 and thereafter	280,000,000
Indefinite	86,500,000
Total	383,300,000
Research Tax Credit Carryforward \| State
Expirations of Tax Credit Carryforwards [Abstract]
2019	0
2020	0
2021	0
2022	0
2023	0
2024 and thereafter	0
Indefinite	2,700,000
Total	2,700,000
Research Tax Credit Carryforward \| Federal
Expirations of Tax Credit Carryforwards [Abstract]
2019	0
2020	0
2021	0
2022	0
2023	0
2024 and thereafter	13,800,000
Indefinite	0
Total	$ 13,800,000

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits Activity (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of the year	$ 8,313,000	$ 6,855,000	$ 5,455,000
Increases related to current year tax positions	1,319,000	1,532,000	1,183,000
Decreases related to prior year tax positions	0	(74,000)
Increase related to prior year tax positions			217,000
Balance at end of the year	$ 9,632,000	$ 8,313,000	$ 6,855,000

401(k) Plan (Details)

401(k) Plan (Details) - USD ($) $ in Thousands	12 Months Ended
401(k) Plan (Details) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Retirement Benefits [Abstract]
Employer matching contribution, percent	50.00%
Maximum annual contribution per employee, percent	6.00%
Company's contribution to 401(k) plan	$ 1,200	$ 822	$ 496

Related Party Transactions (Det

Related Party Transactions (Details) - USD ($)	1 Months Ended					12 Months Ended
Related Party Transactions (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2016	Jan. 31, 2016	May 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2013	Dec. 31, 2010
Related Party Transaction [Line Items]
Full payment						$ 0	$ 1,000,000	$ 1,000,000
Long-term other assets	$ 2,639,354					2,669,998	2,639,354
Grant proceeds received						9,500,000
Plumbline Life Sciences
Related Party Transaction [Line Items]
Revenue from related parties						107,000	215,000
Accounts receivable	370,000					$ 478,000	370,000
Available-for-sale Securities
Related Party Transaction [Line Items]
Number of shares owned (shares)						395,758
GeneOne (affiliated entity)
Related Party Transaction [Line Items]
Payment received for license granted										$ 3,000,000
Term									20 years
Ownership target				35.00%	35.00%
Full payment	1,000,000
Revenue from related parties						$ 342,000	551,000	1,200,000
Operating expenses related to affiliated entity						7,000,000	2,300,000	$ 2,800,000
Accounts payable/accrued liability	107,000					372,000	107,000
Long-term other assets	331,000					$ 381,000	331,000
Number of shares owned (shares)						1,644,155
Director
Related Party Transaction [Line Items]
Term			5 years
Revenue from related parties							2,600,000
Operating expenses related to affiliated entity						$ 1,800,000	2,300,000
Accounts receivable	117,000					258,000	117,000
Expenses to reimburse			$ 3,100,000
Proceeds from sub-grant		$ 6,100,000
Grant proceeds received						3,300,000
Due to related parties	$ 820,000					$ 554,000	$ 820,000

Quarterly Financial Informati_3

Quarterly Financial Information (Unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disaggregation of Revenue [Line Items]
Total revenues	$ 2,502,624	$ 2,000,868	$ 24,448,761	$ 1,529,644	$ 8,787,234	$ 2,644,543	$ 20,412,124	$ 10,376,185	$ 30,481,897	$ 42,220,086	$ 35,368,361
Research and development	26,365,647	21,851,858	22,462,620	24,577,751	24,641,124	25,510,239	23,878,751	24,542,504	95,257,876	98,572,618	88,712,035
General and administrative	5,636,141	6,791,693	7,189,310	9,698,015	8,033,899	6,319,775	6,169,106	7,767,589	29,315,159	28,290,369	23,892,263
Gain on sale of assets					1,000,000	0	0	0	0	1,000,000	1,000,000
Total operating expenses	32,001,788	28,643,551	29,651,930	34,275,766	31,675,023	31,830,014	30,047,857	32,310,093	124,573,035	125,862,987	111,604,298
Loss from operations	(29,499,164)	(26,642,683)	(5,203,169)	(32,746,122)	(22,887,789)	(29,185,471)	(9,635,733)	(21,933,908)	(94,091,138)	(83,642,901)	(76,235,937)
Interest and other income, net	(169,300)	380,987	396,681	312,523	509,266	463,346	300,021	340,341	920,891	1,612,974	1,257,257
Change in fair value of common stock warrants	0	228,665	259,971	(127,841)	579,546	423,296	(312,500)	116,477	360,795	806,819	127,554
Gain (loss) from investment in affiliated entity	(3,293,741)	1,017,359	(2,092,608)	2,380,423	292,798	(5,835,741)	169,096	(1,608,817)	(1,988,567)	(6,982,664)	1,110,787
Net loss before provision for income tax	(32,962,205)	(25,015,672)	(6,639,125)	(30,181,017)					(94,798,019)	(88,205,772)	(73,740,339)
Provision for income taxes	0	0	0	2,169,811					2,169,811	0	0
Net loss	$ (32,962,205)	$ (25,015,672)	$ (6,639,125)	$ (32,350,828)	$ (21,506,179)	$ (34,134,570)	$ (9,479,116)	$ (23,085,907)	$ (96,967,830)	$ (88,205,772)	$ (73,740,339)
Net loss per share
Basic ($ per share)	$ (0.34)	$ (0.27)	$ (0.07)	$ (0.36)	$ (0.24)	$ (0.39)	$ (0.13)	$ (0.31)	$ (1.05)	$ (1.08)	$ (1.01)
Diluted ($ per share)	$ (0.34)	$ (0.27)	$ (0.08)	$ (0.36)	$ (0.24)	$ (0.40)	$ (0.13)	$ (0.31)	$ (1.05)	$ (1.09)	$ (1.01)
Revenue under collaborative research and development arrangements
Disaggregation of Revenue [Line Items]
Total revenues	$ 2,372,600	$ 1,813,287	$ 24,385,852	$ 1,289,046	$ 7,409,214	$ 351,272	$ 16,358,316	$ 4,288,586	$ 29,860,785	$ 28,407,388	$ 6,490,747
Revenue under collaborative research and development arrangements with affiliated entity
Disaggregation of Revenue [Line Items]
Total revenues	56,207	184,990	60,319	148,008	226,486	129,133	176,879	233,330	449,524	765,828	1,400,594
Grants and miscellaneous revenue
Disaggregation of Revenue [Line Items]
Total revenues	$ 73,817	$ 2,591	$ 2,590	$ 92,590	980,443	1,456,216	2,797,647	5,240,233	171,588	10,474,539	27,136,457
Grants and miscellaneous revenue from affiliated entity
Disaggregation of Revenue [Line Items]
Total revenues					$ 171,091	$ 707,922	$ 1,079,282	$ 614,036	$ 0	$ 2,572,331	$ 340,563

Subsequent Events (Details)

Subsequent Events (Details) - 6.50% Convertible Senior Notes Due 2024 - Convertible Debt $ / shares in Units, $ in Millions	Mar. 01, 2019USD ($)day$ / shares	Feb. 19, 2019	Mar. 12, 2019USD ($)	Dec. 31, 2018
Subsequent Event [Line Items]
Stated interest rate				6.50%
Subsequent Event
Subsequent Event [Line Items]
Debt instrument, face amount \| $	$ 78.5		$ 78.5
Proceeds from issuance of debt \| $	$ 75.8		$ 75.8
Debt instrument, convertible, conversion ratio		0.1858045
Debt instrument, convertible, conversion price (in dollars per share) \| $ / shares	$ 5.38
Debt instrument, convertible, threshold percentage of stock price trigger	130.00%
Debt instrument, convertible, threshold trading days \| day	20
Debt instrument, convertible, threshold consecutive trading days \| day	30
Debt instrument, redemption price, percentage	100.00%