Condensed Financial Statements of Parent Company (Schedule of Condensed Statements of Cash Flows) (Detail) - USD ($) $ in Thousands		12 Months Ended
	Feb. 15, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Financial Statements, Captions [Line Items]
Net income		$ 279,328	$ 277,977	$ 237,866
Stock-based compensation		12,737	12,503	11,963
Excess tax benefits from stock-based compensation		(1,389)	(3,183)	(2,686)
Net cash from operating activities		393,471	286,670	173,606
Net cash received in acquisitions		0	830,661	(1,896)
Net cash from investing activities		(1,238,920)	(2,282,093)	(385,922)
Proceeds from stock option exercises		14,853	29,158	68,653
Excess tax benefits from stock-based compensation		1,389	3,183	2,686
Proceeds from issuance of preferred stock	$ 144,500	0	0	144,486
Purchase of treasury stock		(101,237)	(1,457)	(144,630)
Cash dividends paid on preferred stock		(8,063)	(8,063)	(6,719)
Cash dividends paid on common stock		(132,161)	(127,178)	(119,619)
Net cash from financing activities		72,849	1,803,421	1,243,462
Net change in cash and cash equivalents		(772,600)	(192,002)	1,031,146
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net income		279,328	277,977	237,866
Equity in undistributed earnings of subsidiaries		(155,755)	(165,569)	(97,756)
Stock-based compensation		480	441	330
Excess tax benefits from stock-based compensation		(161)	(165)	(155)
Net change in other assets and other liabilities		2,621	(1,984)	2,372
Net cash from operating activities		126,513	110,700	142,657
Redemption of investment in Frost Securities, Inc.		216	0	0
Net cash received in acquisitions		0	830,661	0
Capital contribution to subsidiaries		0	(879,730)	0
Net cash from investing activities		216	(49,069)	0
Proceeds from stock option exercises		14,853	29,158	68,653
Proceeds from stock-based compensation activities of subsidiaries		12,257	12,062	11,633
Excess tax benefits from stock-based compensation		161	165	155
Proceeds from issuance of preferred stock		0	0	144,486
Purchase of treasury stock		(101,237)	(1,457)	(144,630)
Cash dividends paid on preferred stock		(8,063)	(8,063)	(6,719)
Cash dividends paid on common stock		(132,161)	(127,178)	(119,619)
Net cash from financing activities		(214,190)	(95,313)	(46,041)
Net change in cash and cash equivalents		(87,461)	(33,682)	96,616
Cash and cash equivalents at beginning of year		293,995	327,677	231,061
Cash and cash equivalents at end of year		$ 206,534	$ 293,995	$ 327,677