License and Collaboration Agreement - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended				9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Deferred revenue - related party
Balance at beginning of period			$ 8,223		$ 8,223
Balance at End of Period	$ 16,478				16,478
Payable to collaboration partner - related party
Balance at Beginning of Period			1,061		1,061
Balance at End of Period	1,020				1,020
Revenue recognized from contract liability balance at beginning of period	2,900			$ 5,900	4,500	$ 27,900
Costs to obtain or fulfill the contract that were capitalized	0			0	0	0
Janssen Biotech, Inc. | License and Collaboration Agreement
Receivable from collaboration partner - related party
Balance at beginning of period			2,042		2,042	1,816
Additions					30,882	6,012
Deductions					(31,905)	(3,242)
Balance at end of period	1,019			4,586	1,019	4,586
Contract asset - related party
Contract asset - related party, Balance at Beginning of Period			2,545		2,545
Contract asset - related party, Additions					926
Contract asset - related party, Deductions					(2,545)
Contract asset - related party, Balance at end of Period	926				926
Deferred revenue - related party
Balance at beginning of period			8,223		8,223	31,752
Additions					36,441	4,147
Deductions		$ (109,200)	(60,600)		(5,986)	(27,929)
Balance at End of Period	38,678			7,970	38,678	7,970
Payable to collaboration partner - related party
Balance at Beginning of Period			$ 1,061		1,061
Additions					1,226	1,068
Deductions					(1,267)	(304)
Balance at End of Period	$ 1,020			$ 764	$ 1,020	$ 764