Condensed Parent Company Financial Statements (Detail) - Statements of Income (Parent Company Only) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income
Interest income	$ 335,984	$ 299,864	$ 287,247
Net losses on early extinguishment of debt	0	(2,059)	(1,034)
Securities transactions and other	2,764	4,567	4,452
Expenses
Interest expense	24,386	23,012	27,115
Other expenses	21,601	20,135	17,358
Income before income tax expense	119,811	100,476	128,021
Income tax benefit (expense)	(37,747)	(31,170)	(48,715)
Net income	82,064	69,306	79,306
Net income applicable to non-vested restricted shares	(882)	(836)	(1,107)
Net income applicable to common shares	81,182	68,470	78,199
Parent Company
Income
Dividends from subsidiaries	127,000	56,881	54,200
Interest income	2,164	1,502	1,067
Net losses on early extinguishment of debt	0	0	(1,034)
Securities transactions and other	584	6,451	37,485
Total income	129,748	64,834	91,718
Expenses
Interest expense	12,545	12,062	13,607
Salaries and employee benefits	14,624	12,589	15,198
Other expenses	6,003	5,867	5,792
Total expenses	33,172	30,518	34,597
Income before income tax expense	96,576	34,316	57,121
Income tax benefit (expense)	11,950	8,710	(962)
Income before equity in undistributed (loss) income of subsidiaries	108,526	43,026	56,159
Equity in undistributed (loss) income of subsidiaries	(26,462)	26,280	23,147
Net income	82,064	69,306	79,306
Net income applicable to non-vested restricted shares	(882)	(836)	(1,107)
Net income applicable to common shares	$ 81,182	$ 68,470	$ 78,199