Operating Segments (Summary of Operating Results by Segment) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Net interest income (expense)	$ 1,558,664	$ 1,291,283	$ 984,867
Credit loss expense	46,171	3,000	63
Non-interest income	428,542	404,818	386,728
Non-interest expense	1,228,662	1,024,274	881,994
Income before income taxes	712,373	668,827	489,538
Income tax expense (benefit)	114,400	89,677	46,459
Net income	597,973	579,150	443,079
Preferred stock dividends	6,675	6,675	7,157
Net income available to common shareholders	591,298	572,475	435,922
Revenues from (expenses to) external customers	1,987,206	1,696,101	1,371,595
Average assets	49,604,000	51,513,000	45,983,000
Banking [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	1,562,441	1,295,467	989,870
Credit loss expense	46,171	3,000	54
Non-interest income	251,319	230,876	220,662
Non-interest expense	1,077,824	886,421	753,719
Income before income taxes	689,765	636,922	456,759
Income tax expense (benefit)	111,145	85,127	41,483
Net income	578,620	551,795	415,276
Preferred stock dividends	0	0	0
Net income available to common shareholders	578,620	551,795	415,276
Revenues from (expenses to) external customers	1,813,760	1,526,343	1,210,532
Average assets	49,536,000	51,448,000	45,903,000
Frost Wealth Advisors [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	7,620	4,645	2,138
Credit loss expense	0	0	9
Non-interest income	178,906	175,874	167,442
Non-interest expense	144,478	132,009	122,972
Income before income taxes	42,048	48,510	46,599
Income tax expense (benefit)	8,830	10,187	9,786
Net income	33,218	38,323	36,813
Preferred stock dividends	0	0	0
Net income available to common shareholders	33,218	38,323	36,813
Revenues from (expenses to) external customers	186,526	180,519	169,580
Average assets	59,000	57,000	70,000
Non-Banks [Member]
Segment Reporting Information [Line Items]
Net interest income (expense)	(11,397)	(8,829)	(7,141)
Credit loss expense	0	0	0
Non-interest income	(1,683)	(1,932)	(1,376)
Non-interest expense	6,360	5,844	5,303
Income before income taxes	(19,440)	(16,605)	(13,820)
Income tax expense (benefit)	(5,575)	(5,637)	(4,810)
Net income	(13,865)	(10,968)	(9,010)
Preferred stock dividends	6,675	6,675	7,157
Net income available to common shareholders	(20,540)	(17,643)	(16,167)
Revenues from (expenses to) external customers	(13,080)	(10,761)	(8,517)
Average assets	$ 9,000	$ 8,000	$ 10,000