Income Taxes - Components of Consolidated Income Tax Expense (Benefit) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current:
Federal	$ 35,602	$ 28,047	$ 20,811
State	1,603	1,012	684
Total Current	37,205	29,059	21,495
Deferred:
Federal	(2,120)	1,343	(821)
State	(129)	103	(591)
Total Deferred	(2,249)	1,446	(1,412)
Income tax expense, Total	$ 34,956	$ 30,505	$ 20,083