Income Taxes - Effective Tax Rates (Details) - USD ($)	3 Months Ended		12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Effective tax rates differing from U.S. federal statutory rate
U.S. Federal taxes (Benefit) at statutory rate			$ (32,277,000)	$ (24,375,000)
State tax expense			(2,842,000)	(2,428,000)
Research and development credits			(1,449,000)	(751,000)
Stock-based compensation			1,275,000	1,683,000
Mark to market fair value adjustments			49,000	504,000
Other nondeductible items			933,000	841,000
Change in valuation allowance			34,453,000	$ 24,526,000
Provision for income taxes	$ 39,000	$ 103,000	$ 142,000
U.S. Federal taxes (Benefit) at statutory rate (as a percent)			(34.00%)	(34.00%)
State tax expense (as a percent)			(2.99%)	(3.39%)
Research and development credits (as a percent)			(1.53%)	(1.05%)
Stock-based compensation (as a percent)			1.34%	2.35%
Mark to market fair value adjustments (as a percent)			0.05%	0.70%
Other nondeductible items (as a percent)			0.99%	1.17%
Change in valuation allowance (as a percent)			36.29%	34.21%
Provision for income taxes (as a percent)			0.15%
Foreign withholding tax			$ 142,000