Condensed Parent Company Financial Statements (Detail) - Statements of Income (Parent Company Only) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income
Interest income	$ 299,864	$ 287,247	$ 300,569
Net losses on early extinguishment of debt	(2,059)	(1,034)	(558)
Securities transactions and other	4,567	4,452	7,086
Expenses
Interest expense	23,012	27,115	34,901
Other expenses	24,386	19,879	24,777
Income (loss) before income tax expense (benefit)	100,476	128,021	(49,936)
Income tax benefit (expense)	(31,170)	(48,715)	28,882
Net income (loss)	69,306	79,306	(21,054)
Net (income) loss applicable to non-vested restricted shares	(836)	(1,107)	306
Net income (loss) applicable to common shares	68,470	78,199	(20,748)
Parent Company
Income
Dividends from subsidiaries	56,881	54,200	38,000
Interest income	1,502	1,067	619
Net losses on early extinguishment of debt	0	(1,034)	(558)
Securities transactions and other	6,451	37,485	1,982
Total income	64,834	91,718	40,043
Expenses
Interest expense	12,062	13,607	14,840
Salaries and employee benefits	12,589	15,198	13,232
Other expenses	5,867	5,792	5,740
Total expenses	30,518	34,597	33,812
Income (loss) before income tax expense (benefit)	34,316	57,121	6,231
Income tax benefit (expense)	8,710	(962)	13,070
Income before undistributed income (loss) of subsidiaries	43,026	56,159	19,301
Equity in undistributed income (loss) of subsidiaries	26,280	23,147	(40,355)
Net income (loss)	69,306	79,306	(21,054)
Net (income) loss applicable to non-vested restricted shares	(836)	(1,107)	306
Net income (loss) applicable to common shares	$ 68,470	$ 78,199	$ (20,748)