License and Collaboration Agreement - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Deferred revenue - related party
Balance at Beginning of Period				$ 17,738
Balance at End of Period	$ 17,230			17,230		$ 17,738
Payable to collaboration partner - related party
Balance at Beginning of Period				1,262
Balance at End of Period	1,003			1,003		1,262
Revenue recognized from contract liability balance at beginning of period	2,100			3,300
Costs to obtain or fulfill the contract that were capitalized		$ 1,600			$ 1,600
Janssen Biotech, Inc. | License and Collaborative Revenue
Payable to collaboration partner - related party
Revenue recognized from contract liability balance at beginning of period	5,700			9,400
Increase (decrease) in transaction price				300
Janssen Biotech, Inc. | License and Collaboration Agreement
Receivable from collaboration partner - related party
Balance at Beginning of Period			$ 2,042	5,955	2,042	2,042
Additions				4,202	29,881
Deductions				(7,160)	(27,034)
Balance at End of Period	2,997	4,889		2,997	4,889	5,955
Contract asset - related party
Contract asset - related party, Balance at Beginning of Period			2,545	800	2,545	2,545
Contract asset - related party, Additions				342
Contract asset - related party, Deductions				(1,142)	(2,545)
Contract asset - related party, Balance at End of Period						800
Deferred revenue - related party
Balance at Beginning of Period			8,223	41,530	8,223	8,223
Additions				2,977	34,526
Deductions				(10,493)	(1,182)
Balance at End of Period	34,014	41,567		34,014	41,567	41,530
Payable to collaboration partner - related party
Balance at Beginning of Period			1,061	1,262	1,061	1,061
Additions				1,040	625
Deductions				(1,299)	(876)
Balance at End of Period	$ 1,003	810		1,003	810	1,262
Janssen Biotech, Inc. | First Amendment
Payable to collaboration partner - related party
Revenue recognized from contract liability balance at beginning of period				$ 5,000
Increase (decrease) in transaction price		9,400			9,400	$ (9,400)
Janssen Biotech, Inc. | First Amendment | License and Collaborative Revenue
Payable to collaboration partner - related party
Revenue recognized from contract liability balance at beginning of period		25,000
Revenue following contract modification		$ 1,200			$ 1,200
Revenue recognized from performance obligations in previous periods			$ 1,600