Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Tax Credit Carryforward [Line Items]
Deferred tax liabilities as a result of TCJA	$ 34,200
Valuation allowance	$ 83,384	$ 56,737
Period of cumulative changes in ownership interests	3 years
Percentage of cumulative changes in ownership interests	50.00%
Income tax effect	$ (1,758)	$ 193	$ 139
Federal tax authority
Tax Credit Carryforward [Line Items]
Valuation allowance	1,700
Net operating loss carry-forwards	196,200
State tax authority
Tax Credit Carryforward [Line Items]
Net operating loss carry-forwards	271,300
Non-qualified stock options | Federal tax authority
Tax Credit Carryforward [Line Items]
Net operating loss carry-forwards	8,900
Non-qualified stock options | State tax authority
Tax Credit Carryforward [Line Items]
Net operating loss carry-forwards	2,300
Income Tax Expense
Tax Credit Carryforward [Line Items]
Income tax expense recorded in prepaid asset			$ 2,800
Accumulated Deficit
Tax Credit Carryforward [Line Items]
Net operating loss carry-forwards	$ 3,700