Operating Segments - Summary of Operating Results by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	$ 385,266	$ 288,208	$ 785,086	$ 537,279
Credit loss expense	9,901	0	19,005	0
Total non-interest income	103,528	97,927	208,793	199,317
Total non-interest expense	285,042	246,347	570,184	485,079
Income (loss) before income taxes	193,851	139,788	404,690	251,517
Income tax expense (benefit)	31,733	20,674	64,919	33,301
Net income (loss)	162,118	119,114	339,771	218,216
Preferred stock dividends	1,669	1,669	3,338	3,338
Net income (loss) available to common shareholders	160,449	117,445	336,433	214,878
Revenues from (expenses to) external customers	488,794	386,135	993,879	736,596
Bank
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	385,720	289,186	785,857	539,305
Credit loss expense	9,901	1	19,003	0
Total non-interest income	57,808	55,397	121,451	114,103
Total non-interest expense	246,927	211,044	496,794	417,582
Income (loss) before income taxes	186,700	133,538	391,511	235,826
Income tax expense (benefit)	30,636	19,821	62,754	30,835
Net income (loss)	156,064	113,717	328,757	204,991
Preferred stock dividends	0	0	0	0
Net income (loss) available to common shareholders	156,064	113,717	328,757	204,991
Revenues from (expenses to) external customers	443,528	344,583	907,308	653,408
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	2,090	958	3,744	1,658
Credit loss expense	0	(1)	2	0
Total non-interest income	46,147	43,054	88,185	86,283
Total non-interest expense	35,558	33,158	69,505	64,068
Income (loss) before income taxes	12,679	10,855	22,422	23,873
Income tax expense (benefit)	2,663	2,279	4,709	5,013
Net income (loss)	10,016	8,576	17,713	18,860
Preferred stock dividends	0	0	0	0
Net income (loss) available to common shareholders	10,016	8,576	17,713	18,860
Revenues from (expenses to) external customers	48,237	44,012	91,929	87,941
Non-Banks [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	(2,544)	(1,936)	(4,515)	(3,684)
Credit loss expense	0	0	0	0
Total non-interest income	(427)	(524)	(843)	(1,069)
Total non-interest expense	2,557	2,145	3,885	3,429
Income (loss) before income taxes	(5,528)	(4,605)	(9,243)	(8,182)
Income tax expense (benefit)	(1,566)	(1,426)	(2,544)	(2,547)
Net income (loss)	(3,962)	(3,179)	(6,699)	(5,635)
Preferred stock dividends	1,669	1,669	3,338	3,338
Net income (loss) available to common shareholders	(5,631)	(4,848)	(10,037)	(8,973)
Revenues from (expenses to) external customers	$ (2,971)	$ (2,460)	$ (5,358)	$ (4,753)