Operating Segments - Summary of Operating Results by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	$ 268,519	$ 261,791	$ 554,386	$ 525,709
Net income	71,479	73,077	140,258	145,240
Operating Segments [Member] | Banking [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	237,444	230,066	492,717	461,935
Net income	68,195	69,021	134,125	136,739
Operating Segments [Member] | Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	32,225	32,498	63,948	65,140
Net income	4,860	5,299	9,012	10,636
Operating Segments [Member] | Non-Banks [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	(1,150)	(773)	(2,279)	(1,366)
Net income	$ (1,576)	$ (1,243)	$ (2,879)	$ (2,135)