Securities - Securities Available for Sale (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 8,317,505	$ 11,822,584
Gross Unrealized Gains	3,051	261,198
Gross Unrealized Losses	(581,340)	(107,268)
Fair Value	7,739,216	11,976,514
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	763,497	69,551
Gross Unrealized Gains	80	374
Gross Unrealized Losses	(12,825)	(751)
Fair Value	750,752	69,174
U.S. Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	178,406	121,681
Gross Unrealized Gains		3,252
Gross Unrealized Losses	(3,159)	(1)
Fair Value	175,247	124,932
Mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,893,628	7,967,537
Gross Unrealized Gains	567	93,390
Gross Unrealized Losses	(407,610)	(95,872)
Fair Value	4,486,585	7,965,055
State and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,783,759	3,270,160
Gross Unrealized Gains	2,402	161,674
Gross Unrealized Losses	(123,786)	(9,146)
Fair Value	1,662,375	3,422,688
Corporates [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	409,719	316,840
Gross Unrealized Gains	2	2,504
Gross Unrealized Losses	(25,936)	(1,498)
Fair Value	383,785	317,846
Collateralized loan obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	288,496	76,815
Gross Unrealized Gains		4
Gross Unrealized Losses	(8,024)
Fair Value	$ 280,472	$ 76,819