Parent Company Condensed Financial Information - Statements of Net Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Information [Line Items]
Interest expense on long-term debt	$ 790	$ 617	$ 746
Net Income	67,081	57,910	50,539
Parent Company
Condensed Financial Information [Line Items]
Dividends from subsidiaries	75,413	46,414	24,087
Investment income	19	19	15
Interest expense on long-term debt	773	759	769
Other expenses	2,138	2,014	2,579
Income before Equity in Undistributed Net Income of Subsidiaries	72,521	43,660	20,754
Bank subsidiary	(5,064)	13,351	29,926
Nonbank subsidiaries	(376)	899	(141)
Net Income	$ 67,081	$ 57,910	$ 50,539