Operating Segments - Summary of Operating Results by Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	$ 229,344	$ 222,690	$ 685,627	$ 663,356
Net income	60,444	58,669	175,295	177,764
Operating Segments [Member] | Banking [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	201,374	198,244	603,840	588,151
Net income	57,903	56,878	168,038	171,152
Operating Segments [Member] | Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	28,790	26,000	84,272	78,595
Net income	3,800	3,298	11,301	10,917
Operating Segments [Member] | Non-Banks [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	(820)	(1,554)	(2,485)	(3,390)
Net income	$ (1,259)	$ (1,507)	$ (4,044)	$ (4,305)