Income Tax - Components of Income Tax (Benefit) Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current tax provision (benefit)	$ 9,086	$ 12,865	$ (245)
Deferred tax benefit	(4,306)	(4,594)	(3,090)
Income tax expense (benefit)	$ 4,780	$ 8,271	$ (3,335)