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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities:
Net Income		$ 77,102	$ 69,559	$ 72,802	$ 41,965	$ 26,098	$ 39,649	$ 50,065	$ 46,095	$ 261,428	$ 161,907	$ 168,146
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation										19,472	12,204	10,032
Net amortization of premiums and accretion of discounts on borrowings										38,454	46,346	24,310
Losses (gains) on securities transactions, net										2,342	20	(777)
Losses on sales of assets, net										2,402	95	(1,358)
Net change in:
Other assets										(33,145)	(57,353)	47,458
Net cash provided by operating activities										593,589	619,230	419,177
Cash flows from investing activities:
Sales										44,377	2,727	4,782
Cash and cash equivalents acquired in acquisitions										156,612	0	0
Net cash used in investing activities										(3,129,551)	(1,547,548)	(1,527,313)
Cash flows from financing activities:
Proceeds from issuance of preferred stock, net										0	98,101	0
Dividends paid to preferred shareholders										(15,859)	(6,277)	(7,188)
Dividends paid to common shareholders										(138,857)	(115,881)	(111,813)
Purchase of common shares to treasury										(3,801)	(2,645)	(3,191)
Common stock issued, net	$ 106,400									2,704	8,207	112,085
Net cash provided by financing activities										2,548,481	951,927	1,086,837
Net change in cash and cash equivalents										12,519	23,609	(21,299)
Cash and cash equivalents at beginning of year					416,110				392,501	416,110	392,501	413,800
Cash and cash equivalents at end of year	392,501	428,629				416,110				428,629	416,110	392,501
Parent Company
Cash flows from operating activities:
Net Income										261,428	161,907	168,146
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in undistributed earnings of subsidiary										(113,705)	(44,664)	(83,578)
Stock-based compensation										19,472	12,204	10,032
Net amortization of premiums and accretion of discounts on borrowings										63	197	163
Losses (gains) on securities transactions, net										(3)	0	(239)
Losses on sales of assets, net										147	0	0
Net change in:
Other assets										9,928	(89)	8,007
Accrued expenses and other liabilities										(10,657)	8,737	18,381
Net cash provided by operating activities										166,673	138,292	120,912
Cash flows from investing activities:
Sales										257	0	739
Cash and cash equivalents acquired in acquisitions										7,915	0	0
Capital contributions to subsidiary										0	(98,000)	(106,000)
Net cash used in investing activities										8,172	(98,000)	(105,261)
Cash flows from financing activities:
Proceeds from issuance of preferred stock, net										0	98,101	0
Dividends paid to preferred shareholders										(15,859)	(6,277)	(7,188)
Dividends paid to common shareholders										(138,857)	(115,881)	(111,813)
Purchase of common shares to treasury										(3,801)	(2,644)	(3,191)
Common stock issued, net										2,704	8,207	112,085
Net cash provided by financing activities										(155,813)	(18,494)	(10,107)
Net change in cash and cash equivalents										19,032	21,798	5,544
Cash and cash equivalents at beginning of year					$ 90,807				$ 69,009	90,807	69,009	63,465
Cash and cash equivalents at end of year	$ 69,009	$ 109,839				$ 90,807				$ 109,839	$ 90,807	$ 69,009