Condensed Financial Statements of Parent Company (Schedule of Condensed Statements of Cash Flows) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Financial Statements, Captions [Line Items]
Net income	$ 304,261	$ 279,328	$ 277,977
Stock-based compensation	11,799	12,737	12,503
Net tax benefit from stock-based compensation	5,063	1,434	3,202
Net cash from operating activities	437,842	394,860	289,853
Net cash received in acquisitions	(492)	0	830,661
Net cash from investing activities	(1,373,981)	(1,238,920)	(2,282,093)
Proceeds from stock option exercises	78,866	14,853	29,158
Purchase of treasury stock	(1,290)	(101,237)	(1,457)
Cash dividends paid on preferred stock	(8,063)	(8,063)	(8,063)
Cash dividends paid on common stock	(134,902)	(132,161)	(127,178)
Net cash from financing activities	1,486,061	71,460	1,800,238
Net change in cash and cash equivalents	549,922	(772,600)	(192,002)
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net income	304,261	279,328	277,977
Equity in undistributed earnings of subsidiaries	(167,326)	(155,755)	(165,569)
Stock-based compensation	520	480	441
Net tax benefit from stock-based compensation	185	161	165
Net change in other assets and other liabilities	(940)	2,460	(2,149)
Net cash from operating activities	136,700	126,674	110,865
Redemption of investment in Frost Securities, Inc.	0	216	0
Net cash received in acquisitions	0	0	830,661
Capital contribution to subsidiaries	0	0	(879,730)
Net cash from investing activities	0	216	(49,069)
Proceeds from stock option exercises	78,866	14,853	29,158
Proceeds from stock-based compensation activities of subsidiaries	11,279	12,257	12,062
Purchase of treasury stock	(1,290)	(101,237)	(1,457)
Cash dividends paid on preferred stock	(8,063)	(8,063)	(8,063)
Cash dividends paid on common stock	(134,902)	(132,161)	(127,178)
Net cash from financing activities	(54,110)	(214,351)	(95,478)
Net change in cash and cash equivalents	82,590	(87,461)	(33,682)
Cash and cash equivalents at beginning of year	206,534	293,995	327,677
Cash and cash equivalents at end of year	$ 289,124	$ 206,534	$ 293,995