Collaboration and License Agreement - Changes in Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Contract liabilities:
Deferred revenue, Balance at Beginning of Period	$ 33,558	$ 45,000
Deferred revenue, Deductions	(33,558)	(11,442)	$ 28,029
Deferred revenue, Balance at End of Period		33,558	45,000
Contract assets:
Receivable from collaboration partner, Balance at Beginning of Period	$ 1,013	45,000
Receivable from collaboration partner, Deductions		(45,000)
Receivable from collaboration partner, Balance at End of Period		$ 1,013	$ 45,000