Operating Segments - Summary of Operating Results by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	$ 399,820	$ 249,071
Credit loss expense	9,104	0
Total non-interest income	105,265	101,390
Total non-interest expense	285,142	238,732
Income (loss) before income taxes	210,839	111,729
Income tax expense (benefit)	33,186	12,627
Net income (loss)	177,653	99,102
Preferred stock dividends	1,669	1,669
Net income (loss) available to common shareholders	175,984	97,433
Revenues from (expenses to) external customers	505,085	350,461
Bank
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	401,318	250,119
Credit loss expense	9,102	(1)
Total non-interest income	63,643	58,706
Total non-interest expense	249,867	206,538
Income (loss) before income taxes	205,992	102,288
Income tax expense (benefit)	32,366	11,014
Net income (loss)	173,626	91,274
Preferred stock dividends	0	0
Net income (loss) available to common shareholders	173,626	91,274
Revenues from (expenses to) external customers	464,961	308,825
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	1,654	700
Credit loss expense	2	1
Total non-interest income	42,038	43,229
Total non-interest expense	33,947	30,910
Income (loss) before income taxes	9,743	13,018
Income tax expense (benefit)	2,046	2,734
Net income (loss)	7,697	10,284
Preferred stock dividends	0	0
Net income (loss) available to common shareholders	7,697	10,284
Revenues from (expenses to) external customers	43,692	43,929
Non-Banks [Member]
Segment Reporting Information [Line Items]
Interest Income (Expense), Net	(3,152)	(1,748)
Credit loss expense	0	0
Total non-interest income	(416)	(545)
Total non-interest expense	1,328	1,284
Income (loss) before income taxes	(4,896)	(3,577)
Income tax expense (benefit)	(1,226)	(1,121)
Net income (loss)	(3,670)	(2,456)
Preferred stock dividends	1,669	1,669
Net income (loss) available to common shareholders	(5,339)	(4,125)
Revenues from (expenses to) external customers	$ (3,568)	$ (2,293)