Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended			36 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Jan. 01, 2018
Summary of significant accounting policies
Cash and cash equivalents original maturity dates	90 days
Short-term investments maturity period description	Short-term investments consist of debt securities classified as available-for-sale and have maturities greater than 90 days, but less than one year, from the date of acquisition.
Provision for doubtful accounts	$ 0	$ 0	$ 0
Impairment loss of long-lived assets				$ 0
Current assets	252,062	176,371		252,062
Accumulated deficit	(460,452)	(365,512)		(460,452)
Unbilled revenue	750	5,000		750
Current liabilities	$ 22,220	17,728		22,220
Uncharged license fees		$ 1,000
Minimum [Member]
Summary of significant accounting policies
Estimated useful lives	3 years
Maximum [Member]
Summary of significant accounting policies
Estimated useful lives	5 years
ASU 2014-09 | Adjustments
Summary of significant accounting policies
Current assets	$ 5,000			5,000
Current liabilities	1,000			1,000
ASU 2014-09 | Adjustments | Kyowa Hakko Kirin
Summary of significant accounting policies
Current assets					$ 5,000
Accumulated deficit					4,000
Unbilled revenue	$ 0			$ 0
Current liabilities					$ 1,000