Operating Segments (Summary Of Operating Results By Segment) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	$ 222,690	$ 224,578	$ 663,356	$ 653,795
Net income (loss)	58,669	54,507	177,764	162,121
Banking [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	198,244	202,520	588,151	587,382
Net income (loss)	56,878	53,497	171,152	160,788
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	26,000	24,548	78,595	74,256
Net income (loss)	3,298	2,696	10,917	7,299
Non-Banks [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	(1,554)	(2,490)	(3,390)	(7,843)
Net income (loss)	$ (1,507)	$ (1,686)	$ (4,305)	$ (5,966)