Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands		Jun. 30, 2019	Dec. 31, 2018		Jan. 01, 2018
Summary of significant accounting policies
Current assets		$ 127,241	$ 176,371	[1]
Accumulated deficit		(417,123)	(365,512)	[1]
Unbilled license revenue	[1]		5,000
Current liabilities		16,333	17,728	[1]
Uncharged license fees	[1]		$ 1,000
Kyowa Hakko Kirin [Member]
Summary of significant accounting policies
Unbilled license revenue		0
ASU 2014-09 | Adjustments | Kyowa Hakko Kirin [Member]
Summary of significant accounting policies
Current assets					$ 5,000
Accumulated deficit					4,000
Unbilled license revenue		$ 0
Current liabilities					$ 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.