Operating Segments - Summary of Operating Results by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	$ 295,868	$ 268,519	$ 588,077	$ 554,386
Net income	85,553	71,507	170,494	140,323
Operating Segments [Member] | Banking [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	261,250	237,444	520,161	492,717
Net income	81,529	68,223	162,398	134,190
Operating Segments [Member] | Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	36,712	32,225	71,300	63,948
Net income	6,279	4,860	11,573	9,012
Operating Segments [Member] | Non-Banks [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	(2,094)	(1,150)	(3,384)	(2,279)
Net income	$ (2,255)	$ (1,576)	$ (3,477)	$ (2,879)