Operating Segments - Summary of Operating Results by Segment (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	$ 276,621	$ 270,359	$ 831,007	$ 796,068
Net income	80,219	75,850	220,542	221,090
Operating Segments [Member] | Banking [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	244,343	239,145	737,060	701,080
Net income	76,347	71,402	210,454	208,141
Operating Segments [Member] | Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	33,536	31,727	97,484	96,867
Net income	4,797	4,782	13,809	15,418
Operating Segments [Member] | Non-Banks [Member]
Segment Reporting Information [Line Items]
Revenues from (expenses to) external customers	(1,258)	(513)	(3,537)	(1,879)
Net income	$ (925)	$ (334)	$ (3,721)	$ (2,469)