Collaboration and License Agreement - Changes in Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Contract liabilities:
Deferred revenue, Balance at Beginning of Period	$ 33,558	$ 45,000
Deferred revenue, Deductions	(5,331)	(2,410)
Deferred revenue, Balance at End of Period	28,227	42,590
Contract assets:
Receivable from collaboration partner, Balance at Beginning of Period	$ 1,013	45,000
Receivable from collaboration partner, Deductions		$ (45,000)