Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax [Line Items]
Deferred tax asset, valuation allowance		$ 44,389,000	$ 58,202,000
Deferred tax asset, valuation allowance decrease		$ 13,800,000
Number of years cumulative pre-tax loss		3 years
Unrecognized tax benefits		$ 4,440,000	$ 9,331,000	$ 10,359,000
Uncertain tax benefits that, if realized, would affect the effective tax rate		3,700,000
Reduction in unrecognized tax benefit within the next 12 months		100,000
Accrued interest and penalties		0
Decrease in accrued interest and penalties		1,200,000
Operating loss carryforwards state		85,200,000
Operating loss carryforwards federal		$ 120,400,000
Federal and state net operating loss carryforwards, expiring year		2037
Federal research and development tax credit carryforwards		$ 3,400,000
State research and development tax credit carryforwards		3,100,000
Operating loss carryforwards foreign		$ 6,500,000
Federal statutory rate		35.00%	35.00%
Tax cuts and jobs act, income tax benefit		$ 36,000
Provisional amount related to the re-measurement of deferred tax balance		$ 21,000,000
Forecast
Income Tax [Line Items]
Federal statutory rate	21.00%
Federal research and development tax credits [Member]
Income Tax [Line Items]
Federal research and development tax credits expiration year		2037