Revenue from Contracts with Customers (Narrative) (Details)											1 Months Ended					3 Months Ended								12 Months Ended
	Jan. 23, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 20, 2018 USD ($) Agreement Program Option $ / shares shares	Sep. 20, 2018	Jan. 02, 2018 USD ($)	Feb. 14, 2017 USD ($)	Feb. 14, 2017	Nov. 30, 2015 Program	Feb. 19, 2015 USD ($) Program	Jan. 09, 2015 USD ($) Program shares	Nov. 30, 2019 USD ($)	Feb. 28, 2017 $ / shares shares	Mar. 31, 2012 USD ($)	Jul. 31, 2007 USD ($)	Jul. 31, 2006 USD ($)	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)
Revenue From Contract With Customer [Line Items]
Shares sold at the market, value																									$ 44,919,000	$ 5,560,000
Revenue recognized																$ 34,502,000	$ 19,940,000	$ 15,715,000	$ 79,891,000	$ 6,451,000	$ 12,802,000	$ 15,895,000	$ 1,636,000	$ 150,048,000	36,784,000	42,877,000
Non-cash royalty revenue recognized																								30,424,000
Decrease in deferred revenue																								53,900,000	(397,000)	(2,722,000)
Contract with customer, liability, revenue recognized																								22,638,000
Asset impairment charges																								0
Deferred revenue, Additions																								77,000,000
Capitalized contract , cost																0								0
GSK Supply Agreement [Member]
Revenue From Contract With Customer [Line Items]
Milestone payments for license costs															$ 5,000,000									5,000,000
Additional fixed fee for license costs														$ 7,300,000
Negotiation right expiry date													2017-03
Proceeds from negotiation right													$ 9,000,000
Proceeds from negotiation right creditable against future royalty payments													$ 2,500,000
Revenue fixed payments																								19,300,000
UroGen License Agreement [Member]
Revenue From Contract With Customer [Line Items]
Proceeds from collaborators											$ 10,000,000
Revenue recognized																								10,000,000
Transaction price recognized											10,000,000
GSK Agreements [Member]
Revenue From Contract With Customer [Line Items]
Royalty payments on net sales (as a percent)													2.00%
Total potential proceeds from license																										24,300,000
Period to receive license fees													10 years
Milestone method revenue recognized																								15,100,000
Non-cash royalty revenue recognized																								30,400,000	17,300,000
Decrease to stockholders' deficit																								2,500,000
Decrease in deferred revenue																								2,500,000
Merck Collaboration and License Agreement [Member]
Revenue From Contract With Customer [Line Items]
Potential Payments																								85,500,000
Percentage of future royalties on worldwide product sales				67.00%
License and Collaboration Revenue [Member] | Merck Collaboration and License Agreement [Member]
Revenue From Contract With Customer [Line Items]
Revenue recognized																								0
Upfront License Fee [Member]
Revenue From Contract With Customer [Line Items]
Revenue recognized																								75,500,000
Upfront License Fee [Member] | GSK Supply Agreement [Member]
Revenue From Contract With Customer [Line Items]
Proceeds from collaborators															$ 3,000,000
Upfront License Fee [Member] | UroGen License Agreement [Member]
Revenue From Contract With Customer [Line Items]
Upfront cash payment											$ 10,000,000
Research and Development Revenue [Member]
Revenue From Contract With Customer [Line Items]
Revenue recognized																								99,845,000	19,475,000	42,709,000
Research and Development Revenue [Member] | GSK Agreements [Member]
Revenue From Contract With Customer [Line Items]
Revenue recognized																										1,000,000
Research and Development Revenue [Member] | Merck Collaboration and License Agreement [Member]
Revenue From Contract With Customer [Line Items]
Revenue recognized																									4,000,000	4,000,000
Profit-share Products [Member]
Revenue From Contract With Customer [Line Items]
Milestone payments for license costs										$ 20,000,000
Number of collaboration agreement programs | Program										2
Royalty-bearing Products [Member]
Revenue From Contract With Customer [Line Items]
Milestone payments for license costs										$ 155,000,000
Number of collaboration agreement programs | Program										1
Research and development services [Member]
Revenue From Contract With Customer [Line Items]
Revenue recognized																								1,707,000	4,150,000	14,615,000
Collaborative Arrangement [Member]
Revenue From Contract With Customer [Line Items]
Percentage of profit and costs sharing ratio										50.00%
License Agreement [Member]
Revenue From Contract With Customer [Line Items]
Number of license agreement | Agreement			1
Number of license agreement programs | Program			2
License agreement termination notice period			90 days
Option And License Agreements [Member]
Revenue From Contract With Customer [Line Items]
Number of separate option and license agreements | Option			2
Upfront license exercise fee			$ 50,000,000
Number of option and license agreement | Option			1
Collaboration Agreement Termination Notice Period			90 days
Option And License Agreements [Member] | Development Regulatory and Commercialization Milestones [Member]
Revenue From Contract With Customer [Line Items]
Milestone payments receivable			$ 520,000,000
Stock Purchase Agreement [Member]
Revenue From Contract With Customer [Line Items]
Shares sold at the market, value			$ 30,000,000
Shares sold at the market, shares | shares			11,111,111							7,760,000
Number of shares purchased, price per share | $ / shares			$ 2.70
Percentage of common stock outstanding shares			8.50%
Stock purchase agreement, additional shares indisposable period			12 months
Maximum percentage of voting stock allowed to acquire			15.00%
Stock purchase agreement, additional shares, favorable voting period			12 months
Proceeds from issuance of common stock										$ 35,000,000
Shares sold at the market, shares | shares			11,111,111							7,760,000
Royalty Purchase Agreement [Member] | Merck Collaboration and License Agreement [Member] | XOMA [Member]
Revenue From Contract With Customer [Line Items]
Percentage of sold future royalties right to receive				33.00%
Percentage of sold future milestones right to receive				10.00%
Development Regulatory and Commercialization Milestones [Member]
Revenue From Contract With Customer [Line Items]
Reserved right to elect to co-fund of development costs (as a percent)										30.00%
Gilead Collaboration Agreement [Member]
Revenue From Contract With Customer [Line Items]
Project access fee																								142,500,000
Contract with customer, liability, revenue recognized																									20,600,000
Deferred revenue, Additions																									77,000,000
Contract with customer, net asset liability																56,400,000								56,400,000
Incyte Collaboration Agreement [Member]
Revenue From Contract With Customer [Line Items]
Contract with customer, liability, revenue recognized																									2,000,000
Incyte Collaboration Agreement [Member] | License and Collaboration Revenue [Member]
Revenue From Contract With Customer [Line Items]
Revenue recognized																								86,100,000
Maximum [Member] | UroGen License Agreement [Member]
Revenue From Contract With Customer [Line Items]
Royalty payments on net sales (as a percent)											20.00%
Maximum [Member] | Development Regulatory and Commercialization Milestones [Member] | UroGen License Agreement [Member]
Revenue From Contract With Customer [Line Items]
Potential milestone payments receivable											$ 200,000,000
Maximum [Member] | License Agreement [Member] | Development Regulatory and Commercialization Milestones [Member]
Revenue From Contract With Customer [Line Items]
Potential milestone payments receivable			$ 552,500,000
Maximum [Member] | Option And License Agreements [Member]
Revenue From Contract With Customer [Line Items]
Milestone payments receivable			30,000,000
Maximum [Member] | Development Regulatory and Commercialization Milestones [Member]
Revenue From Contract With Customer [Line Items]
Royalty payments on net sales (as a percent)										12.00%
Minimum [Member] | UroGen License Agreement [Member]
Revenue From Contract With Customer [Line Items]
Royalty payments on net sales (as a percent)											14.00%
Minimum [Member] | Development Regulatory and Commercialization Milestones [Member]
Revenue From Contract With Customer [Line Items]
Royalty payments on net sales (as a percent)										6.00%
Gilead Sciences Incorporation [Member]
Revenue From Contract With Customer [Line Items]
Milestones stated value			22,500,000
Gilead Sciences Incorporation [Member] | License and Research and Development Fees [Member]
Revenue From Contract With Customer [Line Items]
Proceeds from collaborators			120,000,000
Gilead Sciences Incorporation [Member] | Collaborative Arrangement [Member]
Revenue From Contract With Customer [Line Items]
Upfront cash payment	$ 120,000,000
Shares sold at the market, value	$ 30,000,000
Transaction price recognized																								20,600,000
Gilead Sciences Incorporation [Member] | Collaborative Arrangement [Member] | License and Collaboration Revenue [Member]
Revenue From Contract With Customer [Line Items]
Revenue recognized																								$ 86,100,000
Gilead Sciences Incorporation [Member] | Stock Purchase Agreement [Member]
Revenue From Contract With Customer [Line Items]
Shares sold at the market, value			$ 30,000,000
Shares sold at the market, shares | shares			11,110,000
Number of shares purchased, price per share | $ / shares			$ 2.70
Percentage of common stock outstanding shares			8.50%
Stock purchase agreement, additional shares indisposable period			12 months
Maximum percentage of voting stock allowed to acquire			15.00%
Stock purchase agreement, additional shares, favorable voting period			12 months
Shares sold at the market, shares | shares			11,110,000
Gilead Sciences Incorporation [Member] | Maximum [Member] | Collaborative Arrangement [Member]
Revenue From Contract With Customer [Line Items]
Aggregate potential milestones receivable			$ 1,700,000,000
Incyte Corporation [Member]
Revenue From Contract With Customer [Line Items]
Collaboration Agreement Termination Notice Period																								12 months
Transaction price recognized																								$ 2,000,000
Percentage of future royalties on worldwide product sales		67.00%
Number of collaboration agreement programs | Program									4
Discovery period of antibodies development and commercialization period									5 years
Extended discovery period of antibodies development and commercialization period									3 years
Receivables for R & D services																$ 1,200,000								1,200,000
Incyte Corporation [Member] | Adjusted Balance Under ASC 605 [Member]
Revenue From Contract With Customer [Line Items]
Transaction price recognized																									1,300,000
Incyte Corporation [Member] | Agenus Inc [Member]
Revenue From Contract With Customer [Line Items]
Number of collaboration agreement programs | Program								3
Incyte Corporation [Member] | License and Collaboration Revenue [Member]
Revenue From Contract With Customer [Line Items]
Revenue recognized																								3,700,000
Incyte Corporation [Member] | License and Collaboration Revenue [Member] | Adjusted Balance Under ASC 605 [Member]
Revenue From Contract With Customer [Line Items]
Revenue recognized																									15,500,000
Incyte Corporation [Member] | Research and Development Revenue [Member]
Revenue From Contract With Customer [Line Items]
Revenue recognized																										$ 37,300,000
Incyte Corporation [Member] | Research and development services [Member]
Revenue From Contract With Customer [Line Items]
Revenue recognized																								1,700,000
Incyte Corporation [Member] | Research and development services [Member] | Adjusted Balance Under ASC 605 [Member]
Revenue From Contract With Customer [Line Items]
Revenue recognized																									4,200,000
Incyte Corporation [Member] | Collaborative Arrangement [Member]
Revenue From Contract With Customer [Line Items]
Proceeds from collaborators										$ 25,000,000
Royalty payments on net sales (as a percent)							15.00%
Proceeds from milestones recognized																					5,000,000
Upfront payment received related to clinical development									$ 20,000,000
Additional license fees						$ 0
Project access fee						$ 15,000,000			25,000,000															75,200,000	78,600,000
Project access fee received																								15,000,000
Increase in transaction price																								3,400,000
Actual and estimated variable consideration for development costs																								50,200,000
Incyte Corporation [Member] | Collaborative Arrangement [Member] | ASC 606 [Member]
Revenue From Contract With Customer [Line Items]
Decrease to stockholders' deficit					$ 6,400,000
Decrease in deferred revenue					$ 6,400,000
Incyte Corporation [Member] | Collaborative Arrangement [Member] | Adjusted Balance Under ASC 605 [Member]
Revenue From Contract With Customer [Line Items]
Contract with customer, liability, revenue recognized																									10,000,000
Incyte Corporation [Member] | Collaborative Arrangement [Member] | Joint Steering Committee [Member]
Revenue From Contract With Customer [Line Items]
Percentage of expected revenue						50.00%
Total development cost						$ 43,400,000
Incyte Corporation [Member] | Collaborative Arrangement [Member] | Upfront License Fee [Member]
Revenue From Contract With Customer [Line Items]
Proceeds from collaborators									$ 10,000,000															$ 10,000,000
Incyte Corporation [Member] | Stock Purchase Agreement [Member]
Revenue From Contract With Customer [Line Items]
Shares sold at the market, shares | shares												10,000,000
Number of shares purchased, price per share | $ / shares												$ 6.00
Shares sold at the market, shares | shares												10,000,000
Incyte Corporation [Member] | Royalty Purchase Agreement [Member] | XOMA [Member]
Revenue From Contract With Customer [Line Items]
Percentage of sold future royalties right to receive				33.00%
Percentage of sold future milestones right to receive				10.00%
Proceeds from milestones recognized																					$ 5,000,000
Incyte Corporation [Member] | Maximum [Member] | Collaborative Arrangement [Member]
Revenue From Contract With Customer [Line Items]
Potential milestone payments receivable		$ 450,000,000																		$ 450,000,000					$ 450,000,000