Collaboration and License Agreement - Changes in Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Contract liabilities:
Deferred revenue, Balance at Beginning of Period	$ 33,558	$ 45,000
Deferred revenue, Deductions	(11,970)	(5,411)
Deferred revenue, Balance at End of Period	21,588	39,589
Contract assets:
Receivable from collaboration partner, Balance at Beginning of Period	$ 1,013	45,000
Receivable from collaboration partner, Deductions		$ (45,000)