Operating Segments - Summary of Operating Results by Segment (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	$ 258,840	$ 229,344	$ 745,444	$ 685,627
Net income	77,615	60,444	205,273	175,295
Operating Segments [Member] | Banking [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	226,166	201,374	648,638	603,840
Net income	71,563	57,903	191,491	168,038
Operating Segments [Member] | Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	32,662	28,790	96,069	84,272
Net income	5,873	3,800	16,345	11,301
Operating Segments [Member] | Non-Banks [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	12	(820)	737	(2,485)
Net income	$ 179	$ (1,259)	$ (2,563)	$ (4,044)