Operating Segments - Summary of Operating Results by Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	$ 230,593	$ 221,686
Net income (loss) available to common shareholders	55,051	61,033
Banking [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	204,260	196,273
Net income (loss) available to common shareholders	53,553	58,290
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	27,223	25,997
Net income (loss) available to common shareholders	3,238	3,391
Non-Banks [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	(890)	(584)
Net income (loss) available to common shareholders	$ (1,740)	$ (648)