Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Contingency [Line Items]
Change in valuation allowance (excluding impact of Tax Act)	$ 30,704	$ 117,707	$ 40,676
Liability for unrecognized tax benefits	5,395	4,628
Accrued interest and penalties related to uncertain tax positions	2,100	1,900
Unrecognized tax benefits, interest on tax expense	200
Unrecognized tax benefits, tax penalties	0
Deferred tax valuation allowance
Income Tax Contingency [Line Items]
Charged to cost and expenses	$ (14,625)	$ 117,707	$ 40,676