Income Taxes - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Tax Credit Carryforward [Line Items]
Reversal of tax reserve	$ 511	$ 903
Interest and penalty expense recognized related to unrecognized tax benefits	100
Tax Reserve Member
Tax Credit Carryforward [Line Items]
Reversal of tax reserve	300
Unrecognized Tax Benefits Reserve Accrued Interest Member
Tax Credit Carryforward [Line Items]
Reversal of tax reserve	200
Research and development and other tax credit carryforwards
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 21,200