License and Collaboration Agreement - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Deferred revenue - related party
Balance at Beginning of Period	$ 17,738
Balance at End of Period	18,630		$ 17,738
Payable to collaboration partner - related party
Balance at Beginning of Period	1,262
Balance at End of Period	1,116		1,262
Revenue recognized from contract liability balance at beginning of period	1,200	$ 1,200
Costs to obtain or fulfill the contract that were capitalized	0	0
Janssen Biotech, Inc. | License and Collaborative Revenue
Payable to collaboration partner - related party
Revenue recognized from contract liability balance at beginning of period	3,600	1,600
Increase (decrease) in transaction price	700
Janssen Biotech, Inc. | License and Collaboration Agreement
Receivable from collaboration partner - related party
Balance at Beginning of Period	5,955	2,042	2,042
Additions	1,509	1,726
Deductions	(5,012)	(4)
Balance at End of Period	2,452	3,764	5,955
Contract asset - related party
Contract asset - related party, Balance at Beginning of Period	800	2,545	2,545
Contract asset - related party, Additions	342
Contract asset - related party, Deductions		(1,248)
Contract asset - related party, Balance at End of Period	1,142	1,297	800
Deferred revenue - related party
Balance at Beginning of Period	41,530	8,223	8,223
Additions	1,850	342
Deductions	(4,335)	(1,564)
Balance at End of Period	39,045	7,001	41,530
Payable to collaboration partner - related party
Balance at Beginning of Period	1,262	1,061	1,061
Additions	676	150
Deductions	(822)
Balance at End of Period	$ 1,116	$ 1,211	$ 1,262