Operating Segments - Summary of Operating Results by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	$ 390,051	$ 399,820
Credit loss expense	13,650	9,104
Total non-interest income	111,377	105,265
Total non-interest expense	326,217	285,142
Income (loss) before income taxes	161,561	210,839
Income tax expense (benefit)	25,871	33,186
Net income (loss)	135,690	177,653
Preferred stock dividends	1,669	1,669
Net income (loss) available to common shareholders	134,021	175,984
Revenues from (expenses to) external customers	501,428	505,085
Bank
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	391,805	401,318
Credit loss expense	13,650
Total non-interest income	66,380	63,643
Total non-interest expense	286,830	249,865
Income (loss) before income taxes	157,705	205,992
Income tax expense (benefit)	25,635	32,366
Net income (loss)	132,070	173,626
Preferred stock dividends	0	0
Net income (loss) available to common shareholders	132,070	173,626
Revenues from (expenses to) external customers	458,185	464,961
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	1,669	1,654
Credit loss expense	0
Total non-interest income	45,426	42,038
Total non-interest expense	37,973	33,949
Income (loss) before income taxes	9,122	9,743
Income tax expense (benefit)	1,916	2,046
Net income (loss)	7,206	7,697
Preferred stock dividends	0	0
Net income (loss) available to common shareholders	7,206	7,697
Revenues from (expenses to) external customers	47,095	43,692
Non-Banks [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	(3,423)	(3,152)
Credit loss expense	0
Total non-interest income	(429)	(416)
Total non-interest expense	1,414	1,328
Income (loss) before income taxes	(5,266)	(4,896)
Income tax expense (benefit)	(1,680)	(1,226)
Net income (loss)	(3,586)	(3,670)
Preferred stock dividends	1,669	1,669
Net income (loss) available to common shareholders	(5,255)	(5,339)
Revenues from (expenses to) external customers	$ (3,852)	$ (3,568)