Income Taxes - Components of Income Tax Expense Benefit (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current:
Federal									$ 8,378	$ 9,525	$ 9,039
State									1,064	1,004	1,324
Total current									9,442	10,529	10,363
Deferred:
Federal									1,349	9	(1,421)
State									92	73	(329)
Total deferred									1,441	82	(1,750)
Income tax expense (benefit)	$ 2,777	$ 2,582	$ 2,779	$ 2,745	$ 2,491	$ 2,790	$ 2,767	$ 2,563	$ 10,883	$ 10,611	$ 8,613