Operating Segments (Summary of Operating Results by Segment) (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 620,555,000		$ 604,861,000		$ 581,776,000
Provision for loan losses	20,582,000		10,080,000		27,445,000
Non-interest income	302,818,000		288,787,000		290,002,000
Non-interest expense	611,910,000		575,093,000		558,098,000
Income (loss) before income taxes	290,881,000		308,475,000		286,235,000
Income tax expense (benefit)	53,015,000		70,523,000		68,700,000
Net income	237,866,000		237,952,000		217,535,000
Preferred stock dividends	6,719,000		0		0
Net income available to common shareholders	231,147,000		237,952,000		217,535,000
Revenues from (expenses to) external customers	923,373,000		893,648,000		871,778,000
Average assets	22,752,000,000	[1]	20,827,000,000	[1]	18,569,000,000	[1]
Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	621,333,000		605,330,000		588,092,000
Provision for loan losses	20,585,000		10,078,000		27,449,000
Non-interest income	190,767,000		188,440,000		196,226,000
Non-interest expense	513,909,000		485,302,000		469,152,000
Income (loss) before income taxes	277,606,000		298,390,000		287,717,000
Income tax expense (benefit)	50,823,000		69,078,000		71,298,000
Net income	226,783,000		229,312,000		216,419,000
Preferred stock dividends	0
Net income available to common shareholders	226,783,000
Revenues from (expenses to) external customers	812,100,000		793,770,000		784,318,000
Average assets	22,709,000,000	[1]	20,783,000,000	[1]	18,530,000,000	[1]
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	6,586,000		8,013,000		6,323,000
Provision for loan losses	(3,000)		2,000		(4,000)
Non-interest income	107,759,000		96,577,000		91,710,000
Non-interest expense	90,132,000		82,744,000		84,114,000
Income (loss) before income taxes	24,216,000		21,844,000		13,923,000
Income tax expense (benefit)	8,563,000		7,646,000		4,873,000
Net income	15,653,000		14,198,000		9,050,000
Preferred stock dividends	0
Net income available to common shareholders	15,653,000
Revenues from (expenses to) external customers	114,345,000		104,590,000		98,033,000
Average assets	31,000,000	[1]	29,000,000	[1]	26,000,000	[1]
Non-Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	(7,364,000)		(8,482,000)		(12,639,000)
Provision for loan losses	0		0		0
Non-interest income	4,292,000		3,770,000		2,066,000
Non-interest expense	7,869,000		7,047,000		4,832,000
Income (loss) before income taxes	(10,941,000)		(11,759,000)		(15,405,000)
Income tax expense (benefit)	(6,371,000)		(6,201,000)		(7,471,000)
Net income	(4,570,000)		(5,558,000)		(7,934,000)
Preferred stock dividends	6,719,000
Net income available to common shareholders	(11,289,000)
Revenues from (expenses to) external customers	(3,072,000)		(4,712,000)		(10,573,000)
Average assets	$ 12,000,000	[1]	$ 15,000,000	[1]	$ 13,000,000	[1]

[1] Frost Wealth Advisors excludes off balance sheet managed and custody assets with a total fair value of $28.4 billion, $26.2 billion, and $25.2 billion at December 31, 2013, 2012 and 2011.