Operating Segments (Summary of Operating Results by Segment) (Detail) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Segment Reporting Information [Line Items]
Net interest income (expense)		$ 736,632	$ 686,934	$ 620,555
Provision for loan losses		51,845	16,314	20,582
Non-interest income		328,730	320,144	302,818
Non-interest expense		693,718	654,740	611,910
Income before income taxes		319,799	336,024	290,881
Income tax expense (benefit)		40,471	58,047	53,015
Net income		279,328	277,977	237,866
Preferred stock dividends		8,063	8,063	6,719
Net income available to common shareholders		271,265	269,914	231,147
Revenues from (expenses to) external customers		1,065,362	1,007,078	923,373
Average assets		28,062,000	25,768,000	22,752,000
Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)		732,671	683,579	621,333
Provision for loan losses		51,848	16,312	20,585
Non-interest income		205,606	193,883	190,767
Non-interest expense		589,394	549,812	513,909
Income before income taxes		297,035	311,338	277,606
Income tax expense (benefit)		34,997	51,881	50,823
Net income		262,038	259,457	226,783
Preferred stock dividends		0	0	0
Net income available to common shareholders		262,038	259,457	226,783
Revenues from (expenses to) external customers		938,277	877,462	812,100
Average assets	[1]	28,024,000	25,734,000	22,709,000
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)		7,634	6,734	6,586
Provision for loan losses		(3)	2	(3)
Non-interest income		121,489	122,261	107,759
Non-interest expense		98,405	96,330	90,132
Income before income taxes		30,721	32,663	24,216
Income tax expense (benefit)		10,753	11,431	8,563
Net income		19,968	21,232	15,653
Preferred stock dividends		0	0	0
Net income available to common shareholders		19,968	21,232	15,653
Revenues from (expenses to) external customers		129,123	128,995	114,345
Average assets	[1]	36,000	32,000	31,000
Non-Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)		(3,673)	(3,379)	(7,364)
Provision for loan losses		0	0	0
Non-interest income		1,635	4,000	4,292
Non-interest expense		5,919	8,598	7,869
Income before income taxes		(7,957)	(7,977)	(10,941)
Income tax expense (benefit)		(5,279)	(5,265)	(6,371)
Net income		(2,678)	(2,712)	(4,570)
Preferred stock dividends		8,063	8,063	6,719
Net income available to common shareholders		(10,741)	(10,775)	(11,289)
Revenues from (expenses to) external customers		(2,038)	621	(3,072)
Average assets	[1]	$ 2,000	$ 2,000	$ 12,000

[1] Frost Wealth Advisors excludes off balance sheet managed and custody assets with a total fair value of $30.7 billion, $30.5 billion and $29.0 billion at December 31, 2015, 2014 and 2013.