Securities - Gross Unrealized Losses and Fair Value of Investment Securities Available for Sale (Detail) $ in Thousands	Sep. 30, 2022 USD ($) Security	Dec. 31, 2021 USD ($) Security
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	3,350	858
Less than 12 months, Fair Value	$ 5,339,604	$ 5,997,925
Less than 12 months, Unrealized Losses	$ (520,514)	$ (96,520)
12 months or more, Count | Security	306	44
12 months or more, Fair Value	$ 1,749,532	$ 278,234
12 months or more, Unrealized Losses	$ (344,081)	$ (10,748)
Total Count | Security	3,656	902
Total Fair Value	$ 7,089,136	$ 6,276,159
Total Unrealized Losses	$ (864,595)	$ (107,268)
U.S. Treasury [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	60	4
Less than 12 months, Fair Value	$ 681,725	$ 58,867
Less than 12 months, Unrealized Losses	$ (23,225)	$ (751)
12 months or more, Count | Security	4
12 months or more, Fair Value	$ 54,888
12 months or more, Unrealized Losses	$ (4,813)
Total Count | Security	64	4
Total Fair Value	$ 736,613	$ 58,867
Total Unrealized Losses	$ (28,038)	$ (751)
U.S. Agencies [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	29	1
Less than 12 months, Fair Value	$ 171,659	$ 11,149
Less than 12 months, Unrealized Losses	$ (6,675)	$ (1)
Total Count | Security	29	1
Total Fair Value	$ 171,659	$ 11,149
Total Unrealized Losses	$ (6,675)	$ (1)
Mortgage-backed [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	788	344
Less than 12 months, Fair Value	$ 2,589,194	$ 5,404,968
Less than 12 months, Unrealized Losses	$ (310,027)	$ (87,301)
12 months or more, Count | Security	108	13
12 months or more, Fair Value	$ 1,520,143	$ 233,295
12 months or more, Unrealized Losses	$ (295,425)	$ (8,571)
Total Count | Security	896	357
Total Fair Value	$ 4,109,337	$ 5,638,263
Total Unrealized Losses	$ (605,452)	$ (95,872)
State and political subdivisions [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	2,222	357
Less than 12 months, Fair Value	$ 1,295,216	$ 329,042
Less than 12 months, Unrealized Losses	$ (145,050)	$ (6,969)
12 months or more, Count | Security	128	31
12 months or more, Fair Value	$ 100,402	$ 44,939
12 months or more, Unrealized Losses	$ (33,959)	$ (2,177)
Total Count | Security	2,350	388
Total Fair Value	$ 1,395,618	$ 373,981
Total Unrealized Losses	$ (179,009)	$ (9,146)
Corporates [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	210	152
Less than 12 months, Fair Value	$ 292,051	$ 193,899
Less than 12 months, Unrealized Losses	$ (25,877)	$ (1,498)
12 months or more, Count | Security	66
12 months or more, Fair Value	$ 74,099
12 months or more, Unrealized Losses	$ (9,884)
Total Count | Security	276	152
Total Fair Value	$ 366,150	$ 193,899
Total Unrealized Losses	$ (35,761)	$ (1,498)
Collateralized loan obligations [Member]
Gain (Loss) on Investments [Line Items]
Less than 12 months, Count | Security	41
Less than 12 months, Fair Value	$ 309,759
Less than 12 months, Unrealized Losses	$ (9,660)
Total Count | Security	41
Total Fair Value	$ 309,759
Total Unrealized Losses	$ (9,660)