Condensed Financial Statements of Parent Company (Schedule of Condensed Statements of Income) (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Condensed Financial Statements, Captions [Line Items]
Total interest income	$ 642,500	$ 631,612	$ 623,017
Interest expense	21,945	26,751	41,241
Salaries and employee benefits	273,692	258,752	252,028
Other	152,077	139,469	137,593
Income before income taxes and equity in undistributed earnings of subsidiaries	290,881	308,475	286,235
Income tax benefit	(53,015)	(70,523)	(68,700)
Net income	237,866	237,952	217,535
Less: Preferred stock dividends	6,719	0	0
Net income available to common shareholders	231,147	237,952	217,535
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Dividend income paid by Frost Bank	144,642	143,623	128,666
Dividend income paid by non-banks	2,819	3,077	2,069
Interest and other income	79	308	101
Total interest income	147,540	147,008	130,836
Interest expense	7,365	8,512	12,653
Salaries and employee benefits	1,175	1,167	1,163
Other	6,735	6,727	4,468
Total expenses	15,275	16,406	18,284
Income before income taxes and equity in undistributed earnings of subsidiaries	132,265	130,602	112,552
Income tax benefit	7,845	7,463	8,295
Equity in undistributed earnings of subsidiaries	97,756	99,887	96,688
Net income	237,866	237,952	217,535
Less: Preferred stock dividends	6,719	0	0
Net income available to common shareholders	$ 231,147	$ 237,952	$ 217,535