Operating Segments - Summary of Operating Results by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	$ 355,547	$ 246,122	$ 892,826	$ 744,159
Credit loss expense	0	0	0	63
Total non-interest income	99,821	93,189	299,138	277,672
Total non-interest expense	257,898	218,003	742,977	643,399
Income (loss) before income taxes	197,470	121,308	448,987	378,369
Income tax expense (benefit)	27,710	13,333	61,011	36,311
Net income (loss)	169,760	107,975	387,976	342,058
Preferred stock dividends	1,668	1,668	5,006	5,488
Net income (loss) available to common shareholders	168,092	106,307	382,970	336,570
Revenues from (expenses to) external customers	455,368	339,311	1,191,964	1,021,831
Bank
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	356,513	247,381	895,818	748,036
Credit loss expense	(1)	(6)	(1)	57
Total non-interest income	55,994	51,279	170,097	154,003
Total non-interest expense	223,193	185,891	640,775	548,151
Income (loss) before income taxes	189,315	112,775	425,141	353,831
Income tax expense (benefit)	26,520	12,029	57,355	32,811
Net income (loss)	162,795	100,746	367,786	321,020
Preferred stock dividends	0	0	0	0
Net income (loss) available to common shareholders	162,795	100,746	367,786	321,020
Revenues from (expenses to) external customers	412,507	298,660	1,065,915	902,039
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	1,357	536	3,015	1,530
Credit loss expense	1	6	1	6
Total non-interest income	44,263	42,369	130,546	124,512
Total non-interest expense	33,530	31,086	97,598	91,037
Income (loss) before income taxes	12,089	11,813	35,962	34,999
Income tax expense (benefit)	2,539	2,481	7,552	7,350
Net income (loss)	9,550	9,332	28,410	27,649
Preferred stock dividends	0	0	0	0
Net income (loss) available to common shareholders	9,550	9,332	28,410	27,649
Revenues from (expenses to) external customers	45,620	42,905	133,561	126,042
Non-Banks [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	(2,323)	(1,795)	(6,007)	(5,407)
Credit loss expense	0	0	0	0
Total non-interest income	(436)	(459)	(1,505)	(843)
Total non-interest expense	1,175	1,026	4,604	4,211
Income (loss) before income taxes	(3,934)	(3,280)	(12,116)	(10,461)
Income tax expense (benefit)	(1,349)	(1,177)	(3,896)	(3,850)
Net income (loss)	(2,585)	(2,103)	(8,220)	(6,611)
Preferred stock dividends	1,668	1,668	5,006	5,488
Net income (loss) available to common shareholders	(4,253)	(3,771)	(13,226)	(12,099)
Revenues from (expenses to) external customers	$ (2,759)	$ (2,254)	$ (7,512)	$ (6,250)