Income Taxes - Effective Tax Rates (Details) - USD ($) $ in Thousands	3 Months Ended						12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective tax rates differing from U.S. federal statutory rate
U.S. Federal taxes (benefit) at statutory rate							$ (46,206)	$ (32,277)	$ (24,375)
State tax expense							(6,559)	(2,842)	(2,428)
Research and development credits							(1,149)	(1,449)	(751)
Stock-based compensation							(5,036)	1,275	1,683
Change in federal tax rate							44,701
Mark to market fair value adjustments							(390)	49	504
Nondeductible settlement for claims							3,873
Other nondeductible items							1,009	933	841
Change in valuation allowance							10,211	34,453	$ 24,526
Provision for income taxes	$ 181	$ 162	$ 64	$ 47	$ 39	$ 103	$ 454	$ 142
U.S. Federal taxes (benefit) at statutory rate (as a percent)							(34.00%)	(34.00%)	(34.00%)
State tax expense (as a percent)							(4.83%)	(2.99%)	(3.39%)
Research and development credits (as a percent)							(0.85%)	(1.53%)	(1.05%)
Stock-based compensation (as a percent)							(3.71%)	1.34%	2.35%
Change in federal tax rate							32.89%	0.00%	0.00%
Mark to market fair value adjustments (as a percent)							(0.29%)	0.05%	0.70%
Nondeductible settlement for claims (as a percent)							2.85%	0.00%	0.00%
Other nondeductible items (as a percent)							0.74%	0.99%	1.17%
Change in valuation allowance (as a percent)							7.51%	36.29%	34.21%
Provision for income taxes (as a percent)							0.31%	0.15%
Income tax expense	$ 181	$ 162	$ 64	$ 47	$ 39	$ 103	$ 454	$ 142
Foreign income tax expense							200	$ 100
State income tax expense							$ 200