Operating Segments - Summary of Operating Results by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	$ 288,208	$ 257,156	$ 537,279	$ 498,037
Credit loss expense	0	0	0	63
Total non-interest income	97,927	91,247	199,317	184,483
Total non-interest expense	246,347	215,254	485,079	425,396
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	139,788	133,149	251,517	257,061
Income taxes	20,674	15,081	33,301	22,978
Net income	119,114	118,068	218,216	234,083
Less: Preferred stock dividends	1,669	1,669	3,338	3,820
Net Income (Loss) Available to Common Stockholders, Basic	117,445	116,399	214,878	230,263
Revenues from (expenses to) external customers	386,135	348,403	736,596	682,520
Bank
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	289,186	258,450	539,305	500,655
Credit loss expense	1	0	0	63
Total non-interest income	55,397	48,944	114,103	102,724
Total non-interest expense	211,044	183,109	417,582	362,260
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	133,538	124,285	235,826	241,056
Income taxes	19,821	13,605	30,835	20,782
Net income	113,717	110,680	204,991	220,274
Less: Preferred stock dividends	0	0	0	0
Net Income (Loss) Available to Common Stockholders, Basic	113,717	110,680	204,991	220,274
Revenues from (expenses to) external customers	344,583	307,394	653,408	603,379
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	958	508	1,658	994
Credit loss expense	(1)	0	0	0
Total non-interest income	43,054	42,534	86,283	82,143
Total non-interest expense	33,158	30,014	64,068	59,951
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	10,855	13,028	23,873	23,186
Income taxes	2,279	2,736	5,013	4,869
Net income	8,576	10,292	18,860	18,317
Less: Preferred stock dividends	0	0	0	0
Net Income (Loss) Available to Common Stockholders, Basic	8,576	10,292	18,860	18,317
Revenues from (expenses to) external customers	44,012	43,042	87,941	83,137
Non-Banks [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	(1,936)	(1,802)	(3,684)	(3,612)
Credit loss expense	0	0	0	0
Total non-interest income	(524)	(231)	(1,069)	(384)
Total non-interest expense	2,145	2,131	3,429	3,185
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	(4,605)	(4,164)	(8,182)	(7,181)
Income taxes	(1,426)	(1,260)	(2,547)	(2,673)
Net income	(3,179)	(2,904)	(5,635)	(4,508)
Less: Preferred stock dividends	1,669	1,669	3,338	3,820
Net Income (Loss) Available to Common Stockholders, Basic	(4,848)	(4,573)	(8,973)	(8,328)
Revenues from (expenses to) external customers	$ (2,460)	$ (2,033)	$ (4,753)	$ (3,996)