Securities - Summary of Available-for-Sale Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	$ 6,722,336	$ 6,447,510	$ 5,405,189
Securities available-for-sale, Gross Unrealized Holding Gains	8,712	149,380	180,144
Securities available-for-sale, Gross Unrealized Holding Losses	(516,012)	(23,711)	(7,285)
Securities available-for-sale, Estimated Fair Value	6,215,036	6,573,179	5,578,048
U.S. Treasury securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	501,098	126,716
Securities available-for-sale, Gross Unrealized Holding Gains	12	125
Securities available-for-sale, Gross Unrealized Holding Losses	(14,752)
Securities available-for-sale, Estimated Fair Value	486,358	126,841
Obligations of State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	2,419,232	2,638,369	2,490,468
Securities available-for-sale, Gross Unrealized Holding Gains	7,737	116,319	125,612
Securities available-for-sale, Gross Unrealized Holding Losses	(182,365)	(1,217)	(993)
Securities available-for-sale, Estimated Fair Value	2,244,604	2,753,471	2,615,087
Residential Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	3,265,654	3,256,746	2,471,278
Securities available-for-sale, Gross Unrealized Holding Gains	399	23,990	38,619
Securities available-for-sale, Gross Unrealized Holding Losses	(301,149)	(21,287)	(5,711)
Securities available-for-sale, Estimated Fair Value	2,964,904	3,259,449	2,504,186
Commercial Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	423,168	356,207	405,146
Securities available-for-sale, Gross Unrealized Holding Gains	476	8,914	15,822
Securities available-for-sale, Gross Unrealized Holding Losses	(8,819)	(1)
Securities available-for-sale, Estimated Fair Value	414,825	365,120	420,968
Corporate Bonds and Other [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-Sale, Amortized Cost Basis, Total	113,184	69,472	38,297
Securities available-for-sale, Gross Unrealized Holding Gains	88	32	91
Securities available-for-sale, Gross Unrealized Holding Losses	(8,927)	(1,206)	(581)
Securities available-for-sale, Estimated Fair Value	$ 104,345	$ 68,298	$ 37,807

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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