Operating Segments - Summary of Operating Results by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	$ 300,826	$ 276,621	$ 888,903	$ 831,007
Net income	93,131	80,219	263,625	220,542
Operating Segments [Member] | Banking [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	266,582	244,343	786,743	737,060
Net income	88,368	76,347	250,766	210,454
Operating Segments [Member] | Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	36,529	33,536	107,829	97,484
Net income	6,417	4,797	17,990	13,809
Operating Segments [Member] | Non-Banks [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	(2,285)	(1,258)	(5,669)	(3,537)
Net income	$ (1,654)	$ (925)	$ (5,131)	$ (3,721)