Parent Company Information - Schedule of Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Net Income	$ 4,671	$ 35,954	$ 31,991	$ 30,341	$ 25,135	$ 27,682	$ 29,520	$ 33,835	$ 102,957	$ 116,172	$ 131,961
Depreciation and amortization									21,082	19,465	19,712
Stock-based compensation									7,575	7,489	6,055
Net amortization of premiums and accretion of discounts on securities									22,080	26,949	16,229
Gains on securities transactions, net	(6)	$ (157)	$ 92	(2,416)	(643)	$ (103)	$ (7)	8	(2,487)	(745)	(14,678)
Fair value of borrowings hedged by derivative transactions or carried at fair value									1,473	1,364	731
Other assets									(74,589)	15,867	(19,199)
Net cash provided by operating activities									154,929	183,976	285,364
Sales									140,640	62,025	57,003
Purchases									(594,327)	(28,415)	(289,181)
Cash and cash equivalents acquired in acquisitions									201,025	102,025	0
Net cash used in investing activities									(1,700,399)	(511,567)	(786,026)
Proceeds from issuance of long-term borrowings, net									162,792	0	125,000
Proceeds from issuance of preferred stock, net									111,590	0	0
Dividends paid to preferred shareholders									(3,813)	0	0
Dividends paid to common shareholders									(102,279)	(88,119)	(129,271)
Purchase of common shares to treasury									(2,108)	(1,688)	(768)
Common stock issued, net									7,898	5,096	7,839
Net cash provided by financing activities									1,128,863	788,830	16,730
Net change in cash and cash equivalents									(416,607)	461,239	(483,932)
Cash and cash equivalents at beginning of year				830,407				369,168	830,407	369,168	853,100
Cash and cash equivalents at end of year	413,800				830,407				413,800	830,407	369,168
Parent Company [Member]
Net Income									102,957	116,172	131,961
Adjustments to reconcile net income to net cash provided by operating activities:									10,978	(13,663)	(21,494)
Depreciation and amortization									0	18	27
Stock-based compensation									7,575	7,489	6,055
Net amortization of premiums and accretion of discounts on securities									162	163	162
Gains on securities transactions, net									0	0	(14)
Fair value of borrowings hedged by derivative transactions or carried at fair value									0	0	(881)
Other assets									(41,452)	6,632	(5,676)
Accrued expenses and other liabilities									9,604	(1,851)	2,590
Net cash provided by operating activities									89,824	114,960	112,730
Sales									49	46	643
Purchases									0	(500)	0
Cash and cash equivalents acquired in acquisitions									109	14,776	0
Capital contributions to subsidiary									(115,000)	0	0
Increase in Restricted Cash									(100,000)	0	0
Net cash used in investing activities									(214,842)	14,322	643
Proceeds from issuance of long-term borrowings, net									98,897	0	125,000
Proceeds from issuance of preferred stock, net									111,590	0	0
Redemption of junior subordinated debentures									0	0	(142,313)
Dividends paid to preferred shareholders									(3,813)	0	0
Dividends paid to common shareholders									(102,279)	(88,119)	(129,271)
Purchase of common shares to treasury									(2,108)	(1,688)	(768)
Common stock issued, net									7,898	5,096	7,839
Net cash provided by financing activities									110,185	(84,711)	(139,513)
Net change in cash and cash equivalents									(14,833)	44,571	(26,140)
Cash and cash equivalents at beginning of year				$ 78,298				$ 33,727	78,298	33,727	59,867
Cash and cash equivalents at end of year	$ 63,465				$ 78,298				$ 63,465	$ 78,298	$ 33,727