Components of Income Tax Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Expenses [Line Items]
Current income tax expense, Federal	$ 10,181	$ 2,519	$ 9,326
Current income tax expense, State	1,983	136	828
Current income tax expense, Total	12,164	2,655	10,154
Deferred income tax expense (benefit), Federal	(3,400)	5,589	(2,280)
Deferred income tax expense (benefit), State	(511)	117	(931)
Deferred income tax expense (benefit), Total	(3,911)	5,706	(3,211)
Income tax expense	$ 8,253	$ 8,361	$ 6,943