Condensed Financial Statements of Parent Company (Schedule of Condensed Statements of Income) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Condensed Financial Statements, Captions [Line Items]
Total income	$ 2,217,716	$ 1,475,721	$ 1,008,769
Interest expense	659,052	184,438	23,902
Other	229,367	194,701	172,154
Income before income taxes and equity in undistributed earnings of subsidiaries	712,373	668,827	489,538
Income tax benefit	(114,400)	(89,677)	(46,459)
Net income	597,973	579,150	443,079
Preferred stock dividends	6,675	6,675	7,157
Net income available to common shareholders	591,298	572,475	435,922
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Dividend income paid by Frost Bank	279,679	51,711	219,386
Dividend income paid by non-banks	255	109	473
Interest and other income	1,929	0	101
Total income	281,863	51,820	219,960
Interest expense	13,304	8,829	7,141
Salaries and employee benefits	1,668	1,605	1,499
Other	6,653	6,316	5,867
Total expenses	21,625	16,750	14,507
Income before income taxes and equity in undistributed earnings of subsidiaries	260,238	35,070	205,453
Income tax benefit	5,974	5,641	4,899
Equity in undistributed earnings of subsidiaries	331,761	538,439	232,727
Net income	597,973	579,150	443,079
Preferred stock dividends	6,675	6,675	7,157
Net income available to common shareholders	$ 591,298	$ 572,475	$ 435,922