Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Income Taxes
Period over which NOL and tax credit carryforward limitations are applied	1 year
Period of cumulative changes in ownership	3 years
Cumulative changes in ownership	50.00%
Operating loss carryforwards	$ 56,832	$ 46,432
Deferred Tax Assets, Valuation Allowance, Total	73,970	57,757
Unrecognized tax benefits from uncertain tax	$ 0	$ 0
Period over which material changes in unrecognized tax positions are not expected	12 months
ASU 2016-09
Income Taxes
Operating loss carryforwards	$ 1,400
Deferred Tax Assets, Valuation Allowance, Total	1,400
Federal
Income Taxes
Cumulative net operating loss carryforwards	149,300
Tax credit carryforwards	8,400
Excess tax benefit deductions related to the exercise of stock options	1,000
State
Income Taxes
Cumulative net operating loss carryforwards	138,200
Tax credit carryforwards	1,600
Excess tax benefit deductions related to the exercise of stock options	$ 700