Condensed Financial Statements of Parent Company (Schedule of Condensed Statements of Cash Flows) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Financial Statements, Captions [Line Items]
Net income	$ 443,599	$ 454,918	$ 364,149
Stock-based compensation	15,946	13,943	13,013
Net tax benefit from stock-based compensation	2,447	3,865	9,062
Net cash provided by (used in) operating activities	634,090	562,388	538,079
Net cash provided by (used in) investing activities	(1,386,750)	(1,913,320)	(670,595)
Proceeds from issuance of subordinated notes	0	0	98,434
Principal payments on subordinated notes	0	0	(100,000)
Proceeds from stock option exercises	20,770	31,647	67,746
Purchase of treasury stock	(68,793)	(101,010)	(101,473)
Cash dividends paid on preferred stock	(8,063)	(8,063)	(8,063)
Cash dividends paid on common stock	(177,006)	(165,449)	(144,172)
Net cash provided by (used in) financing activities	585,062	253,664	1,044,118
Net change in cash and cash equivalents	(167,598)	(1,097,268)	911,602
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	443,599	454,918	364,149
Equity in undistributed earnings of subsidiaries	(218,190)	(242,485)	(221,440)
Stock-based compensation	780	721	519
Net tax benefit from stock-based compensation	240	304	318
Net change in other assets and other liabilities	22,216	(12,709)	7,665
Net cash provided by (used in) operating activities	248,645	200,749	151,211
Net cash provided by (used in) investing activities	0	0	0
Proceeds from issuance of subordinated notes	0	0	98,434
Principal payments on subordinated notes	0	0	100,000
Proceeds from stock option exercises	20,770	31,647	67,746
Proceeds from stock-based compensation activities of subsidiaries	15,166	13,222	12,494
Purchase of treasury stock	(68,793)	(101,010)	(101,473)
Cash dividends paid on preferred stock	(8,063)	(8,063)	(8,063)
Cash dividends paid on common stock	(177,006)	(165,449)	(144,172)
Net cash provided by (used in) financing activities	(217,926)	(229,653)	(175,034)
Net change in cash and cash equivalents	30,719	(28,904)	(23,823)
Cash and cash equivalents at beginning of year	236,397	265,301	289,124
Cash and cash equivalents at end of year	$ 267,116	$ 236,397	$ 265,301