Operating Segments (Summary of Operating Results by Segment) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 984,867	$ 976,001	$ 1,004,005
Credit loss expense	63	241,230	33,759
Non-interest income	386,728	465,454	363,902
Non-interest expense	881,994	848,904	834,679
Income before income taxes	489,538	351,321	499,469
Income tax expense (benefit)	46,459	20,170	55,870
Net income	443,079	331,151	443,599
Preferred stock dividends	7,157	2,016	8,063
Redemption of preferred stock	0	5,514	0
Net income available to common shareholders	435,922	323,621	435,536
Revenues from (expenses to) external customers	1,371,595	1,441,455	1,367,907
Average assets	45,983,000	37,961,000	32,086,000
Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	989,870	981,441	1,010,368
Credit loss expense	54	241,230	33,758
Non-interest income	220,662	321,136	218,447
Non-interest expense	753,719	718,519	703,121
Income before income taxes	456,759	342,828	491,936
Income tax expense (benefit)	41,483	20,347	55,520
Net income	415,276	322,481	436,416
Preferred stock dividends	0	0	0
Redemption of preferred stock		0
Net income available to common shareholders	415,276	322,481	436,416
Revenues from (expenses to) external customers	1,210,532	1,302,577	1,228,815
Average assets	45,903,000	37,892,000	32,019,000
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	2,138	2,776	4,001
Credit loss expense	9	0	1
Non-interest income	167,442	145,268	145,905
Non-interest expense	122,972	123,630	124,622
Income before income taxes	46,599	24,414	25,283
Income tax expense (benefit)	9,786	5,127	5,308
Net income	36,813	19,287	19,975
Preferred stock dividends	0	0	0
Redemption of preferred stock		0
Net income available to common shareholders	36,813	19,287	19,975
Revenues from (expenses to) external customers	169,580	148,044	149,906
Average assets	70,000	59,000	56,000
Non-Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	(7,141)	(8,216)	(10,364)
Credit loss expense	0	0	0
Non-interest income	(1,376)	(950)	(450)
Non-interest expense	5,303	6,755	6,936
Income before income taxes	(13,820)	(15,921)	(17,750)
Income tax expense (benefit)	(4,810)	(5,304)	(4,958)
Net income	(9,010)	(10,617)	(12,792)
Preferred stock dividends	7,157	2,016	8,063
Redemption of preferred stock		5,514
Net income available to common shareholders	(16,167)	(18,147)	(20,855)
Revenues from (expenses to) external customers	(8,517)	(9,166)	(10,814)
Average assets	$ 10,000	$ 10,000	$ 11,000