Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Impact of Adoption
Net loss	$ (27,862)	$ (24,126)	$ (22,291)	$ (17,019)	$ 10,114	$ (20,724)	$ (25,721)	$ (28,008)	$ (91,298)	$ (64,339)	$ (112,387)
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
Impairment loss of long-lived assets									0
Current assets	176,371				149,712				176,371	149,712		$ 5,000
Current liabilities	17,728				17,871				17,728	17,871		1,000
Accumulated deficit	(365,512)				(278,214)				(365,512)	(278,214)		4,000
Total revenues	85	$ 172	$ 30	$ 2,320	$ 42,000				2,607	42,000
Cost of revenue									$ 466	8,400
Minimum [Member]
Impact of Adoption
Estimated useful lives									3 years
Maximum [Member]
Impact of Adoption
Estimated useful lives									5 years
Licensing
Impact of Adoption
Total revenues									$ 2,320	$ 42,000
Other
Impact of Adoption
Total revenues									287
ASU 2014-09 | Adjustments
Impact of Adoption
Current assets	5,000								5,000			5,000
Current liabilities	1,000								1,000			1,000
Accumulated deficit	4,000								4,000			$ 4,000
ASU 2014-09 | Before topic 606
Impact of Adoption
Current assets	171,371								171,371
Current liabilities	16,728								16,728
Accumulated deficit	$ (369,512)								(369,512)
Cost of revenue									466
ASU 2014-09 | Before topic 606 | Licensing
Impact of Adoption
Total revenues									2,320
ASU 2014-09 | Before topic 606 | Other
Impact of Adoption
Total revenues									$ 287