Income Taxes - Effective Tax Rates (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
Effective tax rates differing from U.S. federal statutory rate
U.S. Federal taxes (benefit) at statutory rate									$ (26,800)	$ (46,206)	$ (32,277)
State tax expense									(4,468)	(6,559)	(2,842)
Research and development credits									(1,164)	(1,149)	(1,449)
Stock-based compensation									(3,148)	(5,036)	1,275
Change in federal tax rate										44,701
Mark to market fair value adjustments									865	(390)	49
Nondeductible settlement for claims									1	3,873
Other nondeductible items									885	1,009	933
Change in valuation allowance									34,150	10,211	34,453
Provision for income taxes	$ (14)	$ 118	$ 113	$ 104	$ 181	$ 162	$ 64	$ 47	$ 321	$ 454	$ 142
U.S. Federal taxes (benefit) at statutory rate (as a percent)									(21.00%)	(34.00%)	(34.00%)
State tax expense (as a percent)									(3.50%)	(4.83%)	(2.99%)
Research and development credits (as a percent)									(0.91%)	(0.85%)	(1.53%)
Stock-based compensation (as a percent)									(2.47%)	(3.71%)	1.34%
Change in federal tax rate									0.00%	32.89%	0.00%
Mark to market fair value adjustments (as a percent)									0.68%	(0.29%)	0.05%
Nondeductible settlement for claims (as a percent)									0.00%	2.85%	0.00%
Other nondeductible items (as a percent)									0.69%	0.74%	0.99%
Change in valuation allowance (as a percent)									26.76%	7.51%	36.29%
Provision for income taxes (as a percent)									0.25%	0.31%	0.15%
Income tax expense	$ (14)	$ 118	$ 113	$ 104	$ 181	$ 162	$ 64	$ 47	$ 321	$ 454	$ 142
Foreign income tax expense									200	200	$ 100
State income tax expense									$ 100	$ 200