Operating Segments (Summary Of Operating Results By Segment) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	$ 221,686	$ 214,092
Net income (loss)	61,033	51,928
Banking [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	196,273	192,265
Net income (loss)	58,290	51,853
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	25,997	24,434
Net income (loss)	3,391	1,670
Non-Banks [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	(584)	(2,607)
Net income (loss)	$ (648)	$ (1,595)