Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Line Items]
Deferred tax assets, valuation allowance	$ 35,337		$ 32,325
Effective tax rates	0.00%	2.00%
Change in valuation allowance	$ 3,012
ASU No. 2016-09 [Member]
Income Tax Disclosure [Line Items]
Unrecognized excess tax benefits of deferred tax assets offset by valuation allowance				$ 6,219
Excess tax benefits recognized in the provision for income taxes offset by valuation allowance	$ 525	$ 179