Securities - Securities Available for Sale (Detail) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 8,898,849	$ 11,822,584
Gross Unrealized Gains	34,387	261,198
Gross Unrealized Losses	(383,143)	(107,268)
Fair Value	8,550,093	11,976,514
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	388,866	69,551
Gross Unrealized Gains	58	374
Gross Unrealized Losses	(6,789)	(751)
Fair Value	382,135	69,174
U.S. Agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	153,489	121,681
Gross Unrealized Gains	554	3,252
Gross Unrealized Losses	(1,265)	(1)
Fair Value	152,778	124,932
Mortgage-backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,679,853	7,967,537
Gross Unrealized Gains	15,184	93,390
Gross Unrealized Losses	(286,815)	(95,872)
Fair Value	5,408,222	7,965,055
State and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,101,114	3,270,160
Gross Unrealized Gains	18,327	161,674
Gross Unrealized Losses	(72,930)	(9,146)
Fair Value	2,046,511	3,422,688
Corporates [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	381,163	316,840
Gross Unrealized Gains	252	2,504
Gross Unrealized Losses	(15,330)	(1,498)
Fair Value	366,085	317,846
Collateralized loan obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	194,364	76,815
Gross Unrealized Gains	12	4
Gross Unrealized Losses	(14)
Fair Value	$ 194,362	$ 76,819