Operating Segments - Summary of Operating Results by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	$ 396,712	$ 385,266	$ 786,763	$ 785,086
Credit loss expense	15,787	9,901	29,437	19,005
Total non-interest income	111,190	103,528	222,567	208,793
Total non-interest expense	316,964	285,042	643,181	570,184
Income (loss) before income taxes	175,151	193,851	336,712	404,690
Income tax expense (benefit)	29,652	31,733	55,523	64,919
Net income (loss)	145,499	162,118	281,189	339,771
Preferred stock dividends	1,669	1,669	3,338	3,338
Net income (loss) available to common shareholders	143,830	160,449	277,851	336,433
Revenues from (expenses to) external customers	507,902	488,794	1,009,330	993,879
Bank
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	398,270	385,720	790,075	785,857
Credit loss expense	15,787	9,901	29,437	19,005
Total non-interest income	62,178	57,808	128,558	121,451
Total non-interest expense	276,196	246,927	563,026	496,792
Income (loss) before income taxes	168,465	186,700	326,170	391,511
Income tax expense (benefit)	28,819	30,636	54,454	62,754
Net income (loss)	139,646	156,064	271,716	328,757
Preferred stock dividends	0	0	0	0
Net income (loss) available to common shareholders	139,646	156,064	271,716	328,757
Revenues from (expenses to) external customers	460,448	443,528	918,633	907,308
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	1,907	2,090	3,576	3,744
Credit loss expense	0	0	0	0
Total non-interest income	49,489	46,147	94,915	88,185
Total non-interest expense	37,875	35,558	75,848	69,507
Income (loss) before income taxes	13,521	12,679	22,643	22,422
Income tax expense (benefit)	2,839	2,663	4,755	4,709
Net income (loss)	10,682	10,016	17,888	17,713
Preferred stock dividends	0	0	0	0
Net income (loss) available to common shareholders	10,682	10,016	17,888	17,713
Revenues from (expenses to) external customers	51,396	48,237	98,491	91,929
Non-Banks [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	(3,465)	(2,544)	(6,888)	(4,515)
Credit loss expense	0	0	0	0
Total non-interest income	(477)	(427)	(906)	(843)
Total non-interest expense	2,893	2,557	4,307	3,885
Income (loss) before income taxes	(6,835)	(5,528)	(12,101)	(9,243)
Income tax expense (benefit)	(2,006)	(1,566)	(3,686)	(2,544)
Net income (loss)	(4,829)	(3,962)	(8,415)	(6,699)
Preferred stock dividends	1,669	1,669	3,338	3,338
Net income (loss) available to common shareholders	(6,498)	(5,631)	(11,753)	(10,037)
Revenues from (expenses to) external customers	$ (3,942)	$ (2,971)	$ (7,794)	$ (5,358)