Parent Company Information - Schedule of Condensed Statements of Cash Flows (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Cash Flow Statements, Captions [Line Items]
Net Income		$ 50,090	$ 42,842	$ 39,027	$ 36,187	$ 4,671	$ 35,954	$ 31,991	$ 30,341	$ 168,146	$ 102,957	$ 116,172
Depreciation and amortization										24,431	21,082	19,465
Stock-based compensation										10,032	7,575	7,489
Net amortization of premiums and accretion of discounts on securities										24,310	22,080	26,949
Gains on securities transactions, net										(777)	(2,487)	(745)
Other assets										46,167	(74,589)	15,867
Net cash provided by operating activities										419,177	154,929	183,976
Sales										4,782	140,640	62,025
Purchases										(679,530)	(594,327)	(28,415)
Cash and cash equivalents acquired in acquisitions										0	201,025	102,025
Net cash used in investing activities										(1,527,313)	(1,700,399)	(511,567)
Proceeds from issuance of long-term borrowings, net										385,000	162,792	0
Proceeds from issuance of preferred stock, net										0	111,590	0
Dividends paid to preferred shareholders										(7,188)	(3,813)	0
Dividends paid to common shareholders										(111,813)	(102,279)	(88,119)
Purchase of common shares to treasury										(3,191)	(2,108)	(1,688)
Common stock issued, net	$ 106,400									112,085	7,898	5,096
Net cash provided by financing activities										1,086,837	1,128,863	788,830
Net change in cash and cash equivalents										(21,299)	(416,607)	461,239
Cash and cash equivalents at beginning of year					413,800				830,407	413,800	830,407	369,168
Cash and cash equivalents at end of year	392,501	392,501				413,800				392,501	413,800	830,407
Parent Company
Condensed Cash Flow Statements, Captions [Line Items]
Net Income										168,146	102,957	116,172
Adjustments to reconcile net income to net cash provided by operating activities:										(83,578)	10,978	(13,663)
Depreciation and amortization										0	0	18
Stock-based compensation										10,032	7,575	7,489
Net amortization of premiums and accretion of discounts on securities										163	162	163
Gains on securities transactions, net										(239)	0	0
Other assets										8,007	(41,452)	6,632
Accrued expenses and other liabilities										18,381	9,604	(1,851)
Net cash provided by operating activities										120,912	89,824	114,960
Sales										739	49	46
Purchases										0	0	(500)
Cash and cash equivalents acquired in acquisitions										0	109	14,776
Capital contributions to subsidiary										(106,000)	(115,000)	0
Subordinated debt issued by subsidiary										0	(100,000)	0
Net cash used in investing activities										(105,261)	(214,842)	14,322
Proceeds from issuance of long-term borrowings, net										0	98,897	0
Proceeds from issuance of preferred stock, net										0	111,590	0
Dividends paid to preferred shareholders										(7,188)	(3,813)	0
Dividends paid to common shareholders										(111,813)	(102,279)	(88,119)
Purchase of common shares to treasury										(3,191)	(2,108)	(1,688)
Common stock issued, net										112,085	7,898	5,096
Net cash provided by financing activities										(10,107)	110,185	(84,711)
Net change in cash and cash equivalents										5,544	(14,833)	44,571
Cash and cash equivalents at beginning of year					$ 63,465				$ 78,298	63,465	78,298	33,727
Cash and cash equivalents at end of year	$ 69,009	$ 69,009				$ 63,465				$ 69,009	$ 63,465	$ 78,298