Income Tax - Components of Income Tax Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Tax Disclosure [Abstract]
Current tax provision	$ 3,073	$ 4,380	$ 8,160	$ 7,887
Deferred tax expense (benefit)	39	(312)	(1,113)	(1,799)
Income tax expense	$ 3,112	$ 4,068	$ 7,047	$ 6,088