Income Taxes - Current and Deferred 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									$ 33,778	$ 27,577	$ 27,667
State									2,337	542	2,168
Total current									36,115	28,119	29,835
Deferred:
Federal									(525)	1,678	4,210
State									851	1,988	1,321
Total deferred									326	3,666	5,531
Income tax expense (benefit)	$ 9,414	$ 9,034	$ 9,601	$ 8,392	$ 9,968	$ 7,913	$ 6,206	$ 7,698	$ 36,441	$ 31,785	$ 35,366