Income Taxes - Provision for Income Taxes Applicable to Income Before Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current:
Federal									$ 18,053	$ 15,661	$ 13,346
State									2,159	2,089	1,684
Deferred:
Federal									10,519	10,047	8,337
State									305	618	353
Total	$ 8,464	$ 5,793	$ 8,085	$ 8,694	$ 8,165	$ 7,768	$ 7,962	$ 4,528	$ 31,036	$ 28,415	$ 23,720