Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue:
Total revenues	$ 150,048	$ 36,784	$ 42,877
Operating expenses:
Research and development	(168,339)	(124,600)	(116,125)
General and administrative	(46,041)	(37,340)	(33,741)
Contingent purchase price consideration fair value adjustment	(5,805)	1,335	3,188
Operating loss	(70,137)	(123,821)	(103,801)
Other income (expense):
Loss on early extinguishment of debt		(10,767)
Non-operating income (expense)	28	(2,183)	1,977
Interest expense, net	(41,451)	(25,273)	(18,868)
Net loss	(111,560)	(162,044)	(120,692)
Dividends on Series A-1 convertible preferred stock	(208)	(207)	(206)
Less: net loss attributable to non-controlling interest	(3,903)	(2,352)
Net loss attributable to Agenus Inc. common stockholders	$ (107,865)	$ (159,899)	$ (120,898)
Per common share data:
Basic and diluted net loss attributable to Agenus Inc. common stockholders	$ (0.80)	$ (1.44)	$ (1.23)
Weighted average number of Agenus Inc. common shares outstanding:
Basic and diluted	134,982	110,772	98,415
Other comprehensive income (loss):
Foreign currency translation gain (loss)	$ 215	$ 630	$ (615)
Pension liability			(25)
Other comprehensive income (loss)	215	630	(640)
Comprehensive loss	(107,650)	(159,269)	(121,538)
Royalty sales milestone [Member]
Revenue:
Total revenues	15,100
Other Revenues [Member]
Revenue:
Total revenues	4,679		168
Research and Development [Member]
Revenue:
Total revenues	99,845	19,475	$ 42,709
Non Cash Royalty Revenue Related To The Sale Of Future Royalties And Milestone [Member]
Revenue:
Total revenues	$ 30,424	$ 17,309