Investment Securities - Amortized Cost and Estimated Fair Value of Investment Securities (Detail) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Investment securities available for sale, amortized cost	$ 11,193,152	$ 3,849,347
Investment securities available for sale, gross unrealized gains	515	115,305
Investment securities available for sale, gross unrealized losses	444,706	8,848
Investment securities available for sale, estimated fair value	10,748,961	3,955,804
Amortized cost for held to maturity	13,529,969	2,734,674
Gross unrealized gains for held to maturity	10,288	59,743
Gross unrealized losses for held to maturity	1,164,837	23,127
Estimated fair value for held to maturity	12,375,420	2,771,290
Equity and other securities, Amortized Cost	933,766	461,516
Equity securities, Gross Unrealized Gains	2,120	4,460
Equity securities, Gross Unrealized Losses	3,945	594
Equity and other securities, Estimated Fair Value	931,941	465,382
Other securities, Amortized cost	780,483	387,742
Other securities, Estimated fair value	780,483	387,742
Total debt securities Amortized cost	24,723,121	6,584,021
Total debt securities Gross unrealized gains	10,803	175,048
Total debt securities Gross unrealized losses	1,609,543	31,975
Total debt securities Estimated fair value	23,124,381	6,727,094
Readily marketable securities Amortized cost	153,283	73,774
Readily marketable securities Gross unrealized gains	2,120	4,460
Readily marketable securities Gross unrealized losses	3,945	594
Readily marketable securities Estimated fair value	151,458	77,640
U.S. Treasury and Federal Agencies [Member]
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Investment securities available for sale, amortized cost	7,913,932	682,267
Investment securities available for sale, gross unrealized gains	200	229
Investment securities available for sale, gross unrealized losses	243,172	3,806
Investment securities available for sale, estimated fair value	7,670,960	678,690
Amortized cost for held to maturity	1,054,035	3,052
Gross unrealized losses for held to maturity	45,747	9
Estimated fair value for held to maturity	1,008,288	3,043
Obligations of States and Political Subdivisions [Member]
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Amortized cost for held to maturity	2,577,078	177
Gross unrealized gains for held to maturity	4	2
Gross unrealized losses for held to maturity	116,512
Estimated fair value for held to maturity	2,460,570	179
Commercial [Member]
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Investment securities available for sale, amortized cost	594,779
Investment securities available for sale, gross unrealized losses	20,480
Investment securities available for sale, estimated fair value	574,299
Amortized cost for held to maturity	912,431
Gross unrealized losses for held to maturity	103,528
Estimated fair value for held to maturity	808,903
Residential [Member]
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Investment securities available for sale, amortized cost	2,501,334	3,042,771
Investment securities available for sale, gross unrealized gains	65	113,102
Investment securities available for sale, gross unrealized losses	171,281	561
Investment securities available for sale, estimated fair value	2,330,118	3,155,312
Amortized cost for held to maturity	8,934,918	2,667,328
Gross unrealized gains for held to maturity	1,451	49,221
Gross unrealized losses for held to maturity	891,063	8,376
Estimated fair value for held to maturity	8,045,306	2,708,173
Other Debt Securities [Member]
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Investment securities available for sale, amortized cost	183,107	124,309
Investment securities available for sale, gross unrealized gains	250	1,974
Investment securities available for sale, gross unrealized losses	9,773	4,481
Investment securities available for sale, estimated fair value	173,584	121,802
Amortized cost for held to maturity	1,765	2,562
Estimated fair value for held to maturity	1,765	2,562
Privately Issued [Member]
Schedule Of Amortized Cost And Estimated Fair Value Of Investment Securities [Line Items]
Amortized cost for held to maturity	49,742	61,555
Gross unrealized gains for held to maturity	8,833	10,520
Gross unrealized losses for held to maturity	7,987	14,742
Estimated fair value for held to maturity	$ 50,588	$ 57,333

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