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, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Tax provision computed at the federal statutory rate	$ (25,202)	$ (37,809)	$ (25,217)
State tax, net of federal benefit	(4,827)	(1,849)	(307)
Research credits	(4,884)	(1,176)	(3,232)
Change in tax credit carryforwards	(3,056)	386	11,042
Officers compensation	600	(9,292)	1,196
Stock based compensation	(12,610)	(2,735)	588
Permanent items and other	(116)	1,450	12
Tax differential on foreign earnings	(32)	33	15
Change in tax rate	(1,329)	37,769	(744)
Refundable ATM credit	0	(1,336)	0
Uncertain tax positions	0	(561)	0
Change in prior year deferred taxes	6,595	(1,218)	0
Valuation allowance	44,862	(440)	14,334
Total income tax provision (benefit)	$ 1	$ (16,778)	$ (2,313)