Income Taxes - Components of Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Current tax provision	$ 10,565	$ 22,308	$ 16,991
Deferred tax expense (benefit)	16,904	(987)	(824)
Total provision for income taxes	$ 27,469	$ 21,321	$ 16,167