Income Taxes - Components of Consolidated Income Tax Expense (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 tax expense
Federal									$ 17,401	$ 21,076	$ 14,485
State									7,121	7,139	5,016
Current tax expense, Total									24,522	28,215	19,501
Deferred tax expense (benefit)
Federal									2,735	408	(794)
State									455	273	(199)
Deferred tax benefit, Total									3,190	681	(993)
Total tax expense	$ 7,954	$ 7,694	$ 5,506	$ 6,558	$ 7,388	$ 8,368	$ 7,432	$ 5,708	$ 27,712	$ 28,896	$ 18,508