Investment Securities - Summary of Amortized Cost, Estimated Fair Value and Allowance for Credit Loss on Investments in Debt Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Debt Securities Available for Sale
Amortized Cost	$ 1,857,352	$ 1,883,412
Gross Unrealized Gains	570	2,053
Gross Unrealized Losses	(162,253)	(153,534)
Estimated Fair Value	1,695,669	1,731,931
Debt Securities Held to Maturity
Totals	80,789	90,544
Gross Unrealized Gains	1	5
Gross Unrealized Losses	(4,075)	(3,562)
Estimated Fair Value	76,715	86,987
Obligations of U.S. government agencies
Debt Securities Available for Sale
Amortized Cost	1,217,068	1,174,813
Gross Unrealized Gains	339	1,600
Gross Unrealized Losses	(120,196)	(112,385)
Estimated Fair Value	1,097,211	1,064,028
Debt Securities Held to Maturity
Totals	79,225	88,980
Gross Unrealized Gains	1	5
Gross Unrealized Losses	(4,056)	(3,552)
Estimated Fair Value	75,170	85,433
Obligations of states and political subdivisions
Debt Securities Available for Sale
Amortized Cost	239,510	240,199
Gross Unrealized Gains	72	110
Gross Unrealized Losses	(20,446)	(19,623)
Estimated Fair Value	219,136	220,686
Debt Securities Held to Maturity
Totals	1,564	1,564
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(19)	(10)
Estimated Fair Value	1,545	1,554
Corporate bonds
Debt Securities Available for Sale
Amortized Cost	999	4,981
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(10)	(26)
Estimated Fair Value	989	4,958
Asset backed securities
Debt Securities Available for Sale
Amortized Cost	246,104	270,817
Gross Unrealized Gains	159	131
Gross Unrealized Losses	(948)	(1,428)
Estimated Fair Value	245,315	269,520
Non-agency collateralized mortgage obligations
Debt Securities Available for Sale
Amortized Cost	153,671	192,602
Gross Unrealized Gains	0	209
Gross Unrealized Losses	(20,653)	(20,072)
Estimated Fair Value	$ 133,018	$ 172,739

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 excluding accrued interest, before allowance for credit loss, 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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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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