Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Dec. 31, 2018		Jan. 01, 2018
Summary of significant accounting policies
Current assets		$ 154,312	$ 176,371	[1]
Current liabilities		20,826	17,728	[1]
Accumulated deficit		(391,656)	(365,512)	[1]
Unbilled license revenue	[1]		$ 5,000
ASU 2014-09 | Adjustments | Kyowa Hakko Kirin [Member]
Summary of significant accounting policies
Current assets					$ 5,000
Current liabilities					1,000
Accumulated deficit					$ 4,000
Unbilled license revenue		0
Uncharged license fees reclassed to accounts payable		$ 1,000

[1] Derived from the audited consolidated financial statements included in the Company’s Annual Report on Form 10K for the year ended December 31, 2018.