Parent Company Condensed Financial Information - Statements of Net Income (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Information [Line Items]
Interest expense on long-term debt	$ 617	$ 746	$ 1,107
Other expenses	11,224	10,661	12,815
Net Income	57,910	50,539	34,200
Parent Company [Member]
Condensed Financial Information [Line Items]
Proceeds from Dividends Received	46,414	24,087	35,603
Investment income	19	15	17
Interest expense on long-term debt	759	769	808
Other expenses	2,014	2,579	1,800
Income before Equity in Undistributed Net Income of Subsidiaries	43,660	20,754	33,012
Bank subsidiary	13,351	29,926	1,371
Nonbank subsidiaries	899	(141)	(183)
Net Income	$ 57,910	$ 50,539	$ 34,200