Condensed Financial Statements of Parent Company (Schedule of Condensed Statements of Income) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Condensed Financial Statements, Captions [Line Items]
Interest income	$ 2,390,637	$ 2,217,716	$ 1,475,721
Other	244,411	229,367	194,701
Income before income taxes and equity in undistributed earnings of subsidiaries	695,967	712,373	668,827
Income tax benefit	(113,425)	(114,400)	(89,677)
Net income (loss)	582,542	597,973	579,150
Preferred stock dividends	6,675	6,675	6,675
Net income (loss) available to common shareholders	575,867	591,298	572,475
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Dividend income paid by Frost Bank	262,214	279,679	51,711
Dividend income paid by non-banks	268	255	109
Interest and other income	0	1,929	0
Interest income	262,482	281,863	51,820
Interest expense	13,529	13,304	8,829
Salaries and employee benefits	1,727	1,668	1,605
Other	7,304	6,653	6,316
Total expenses	22,560	21,625	16,750
Income before income taxes and equity in undistributed earnings of subsidiaries	239,922	260,238	35,070
Income tax benefit	6,896	5,974	5,641
Equity in undistributed earnings of subsidiaries	335,724	331,761	538,439
Net income (loss)	582,542	597,973	579,150
Preferred stock dividends	6,675	6,675	6,675
Net income (loss) available to common shareholders	$ 575,867	$ 591,298	$ 572,475