Condensed Financial Information (Parent Company Only) - Condensed Statement of Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating Income (Expense)
Other income									$ 1,103	$ 466	$ 102
Interest expense	(3,310)	(3,372)	(3,402)	(3,419)	(3,457)	(3,720)	(3,517)	(3,628)	(13,503)	(14,322)	(16,501)
Employee benefit expense									(31,032)	(28,383)	(22,875)
Other expense									(58,445)	(54,024)	(46,147)
Income Before Undistributed Income of Subsidiaries									26,924	27,989	16,983
Income Tax Benefit									(7,048)	(8,446)	(4,186)
Net Income	4,115	4,785	5,665	5,311	5,170	4,850	4,910	4,613	19,876	19,543	12,797
Net Income Available to Common Shareholders	4,052	4,719	5,569	5,165	5,014	4,787	4,804	4,457	19,506	19,062	11,472
Parent Company [Member]
Operating Income (Expense)
Dividend income from Bank									7,500	16,500	10,000
Investment income									4		4
Other income									175		17
Interest expense									(2,010)	(1,950)	(1,821)
Employee benefit expense									(811)	(695)	(535)
Other expense									646	(200)	(134)
Income Before Undistributed Income of Subsidiaries									5,504	13,655	7,531
Undistributed Income of Subsidiaries									13,144	4,766	4,288
Income Before Tax									18,648	18,421	11,819
Income Tax Benefit									1,228	1,122	978
Net Income									19,876	19,543	12,797
Preferred stock dividend and discount accretion									(370)	(481)	(1,325)
Net Income Available to Common Shareholders									$ 19,506	$ 19,062	$ 11,472