Income Taxes - Reconciliation of Income Tax (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of federal statutory income tax provision to actual provision
Benefit at federal statutory tax rate	$ (36,967)	$ (29,941)	$ (7,137)
State taxes, net of federal benefit	(11,720)	(4,713)	(1,108)
Share-based compensation	(613)	1,370	5,148
Tax credits	(2,321)	(2,733)	(4,120)
Other	3	492	272
Change in valuation allowance	51,618	(17,817)	6,945
Federal statutory rate change	0	53,342	0
Income tax provision	$ 0	$ 0	$ 0

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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