Operating Segments - Summary of Operating Results by Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	$ 225,690	$ 218,980	$ 456,283	$ 440,666
Net income (loss)	56,975	58,062	112,163	119,095
Operating Segments [Member] | Banking [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	198,206	193,634	402,466	389,907
Net income (loss)	56,582	55,984	110,135	114,274
Operating Segments [Member] | Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	28,259	26,598	55,482	52,595
Net income (loss)	4,263	4,228	7,501	7,619
Operating Segments [Member] | Non-Banks [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	(775)	(1,252)	(1,665)	(1,836)
Net income (loss)	$ (1,182)	$ (2,150)	$ (2,785)	$ (2,798)