Income Taxes - Income Tax Provision (Benefit) Differs from Computed Using Federal Statutory Rate Applied to Income before Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Tax provision computed at the federal statutory rate	$ (37,809)	$ (25,217)	$ (18,269)
State tax, net of federal benefit	(1,849)	(307)	163
Research credits	(1,176)	(3,232)	(2,974)
Change in tax credit carryforwards	386	11,042	(4,965)
Officers compensation	(9,292)	1,196	1,577
Stock based compensation	(2,735)	588	535
Permanent items and other	1,450	12	(487)
Tax differential on foreign earnings	33	15	1,435
Change in tax rate	37,769	(744)	(903)
Refundable ATM credit	(1,336)	0	0
Change in FIN48 Reserve	(561)	0	0
Change in prior year deferred taxes	(1,218)	0	0
Valuation allowance	(440)	14,334	24,294
Total income tax (benefit) provision	$ (16,778)	$ (2,313)	$ 406