Operating Segments - Summary of Operating Results by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	$ 385,426	$ 355,547	$ 1,170,512	$ 892,826
Credit loss expense	11,185	0	30,190	0
Total non-interest income	105,998	99,821	314,791	299,138
Total non-interest expense	293,256	257,898	863,440	742,977
Income (loss) before income taxes	186,983	197,470	591,673	448,987
Income tax expense (benefit)	31,332	27,710	96,251	61,011
Net income (loss)	155,651	169,760	495,422	387,976
Preferred stock dividends	1,668	1,668	5,006	5,006
Net income (loss) available to common shareholders	153,983	168,092	490,416	382,970
Revenues from (expenses to) external customers	491,424	455,368	1,485,303	1,191,964
Bank
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	386,832	356,513	1,172,689	895,818
Credit loss expense	11,185	0	30,190	0
Total non-interest income	62,518	55,994	183,969	170,097
Total non-interest expense	254,747	223,192	751,539	640,774
Income (loss) before income taxes	183,418	189,315	574,929	425,141
Income tax expense (benefit)	31,021	26,520	93,775	57,355
Net income (loss)	152,397	162,795	481,154	367,786
Preferred stock dividends	0	0	0	0
Net income (loss) available to common shareholders	152,397	162,795	481,154	367,786
Revenues from (expenses to) external customers	449,350	412,507	1,356,658	1,065,915
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	2,018	1,357	5,762	3,015
Credit loss expense	0	0	0	0
Total non-interest income	43,903	44,263	132,088	130,546
Total non-interest expense	37,304	33,531	106,811	97,599
Income (loss) before income taxes	8,617	12,089	31,039	35,962
Income tax expense (benefit)	1,809	2,539	6,518	7,552
Net income (loss)	6,808	9,550	24,521	28,410
Preferred stock dividends	0	0	0	0
Net income (loss) available to common shareholders	6,808	9,550	24,521	28,410
Revenues from (expenses to) external customers	45,921	45,620	137,850	133,561
Non-Banks [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	(3,424)	(2,323)	(7,939)	(6,007)
Credit loss expense	0	0	0	0
Total non-interest income	(423)	(436)	(1,266)	(1,505)
Total non-interest expense	1,205	1,175	5,090	4,604
Income (loss) before income taxes	(5,052)	(3,934)	(14,295)	(12,116)
Income tax expense (benefit)	(1,498)	(1,349)	(4,042)	(3,896)
Net income (loss)	(3,554)	(2,585)	(10,253)	(8,220)
Preferred stock dividends	1,668	1,668	5,006	5,006
Net income (loss) available to common shareholders	(5,222)	(4,253)	(15,259)	(13,226)
Revenues from (expenses to) external customers	$ (3,847)	$ (2,759)	$ (9,205)	$ (7,512)