Investment Securities - Additional Information (Detail)	3 Months Ended	6 Months Ended
Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Jun. 30, 2026 USD ($)	Jun. 30, 2025 USD ($)	Dec. 31, 2025 USD ($)
Debt Securities, Held-to-maturity, Restricted	$ 365,500,000		$ 365,500,000		$ 349,200,000
Debt Securities, Available-for-sale, Restricted	591,100,000		591,100,000		624,000,000.0
Other Investments and Securities, at Cost	5,200,000		5,200,000		5,700,000
Federal Home Loan Bank Stock	29,200,000		29,200,000		32,600,000
Amortized Cost	1,183,250,000		1,183,250,000		1,096,232,000
Debt Securities, Available-for-Sale	1,092,201,000		1,092,201,000		1,014,194,000
Gain (Loss) on Equity Securities	0	$ 0	0	$ 5,146,000
Gain Losses Maturities And Impairment	$ 311,000	$ 0	$ 540,000	(5,142,000)
Debt Securities, Available-for-Sale, Unrealized Loss Position, Number of Positions	168		168
Debt Securities, Available-for-Sale, Total Portfolio, Number of Positions	234		234
Residential real estate [Member] \| Senior Lien
Equity Securities Fair Value Gain Loss			$ 5,100,000
FCB Portfolio
Book Value of Available-for-Sale Debt Securities Sold					53,700,000
Sales
Gross Losses			0	5,142,000
Gross Gains			0	0
Gain Losses Maturities And Impairment			$ 0	(5,142,000)
US Government-sponsored Enterprises Debt Securities [Member]
Percent of Unrealized Losses	98.00%		98.00%
Amortized Cost	$ 1,000,000		$ 1,000,000		1,000,000
Debt Securities, Available-for-Sale	$ 999,000		$ 999,000		$ 984,000
Percent of Total Portfolio	96.00%		96.00%
Corporate Debt Securities [Member]
Investment Securities in Unrealized Loss Position, Qualitative Disclosure, Number of Positions, Total	6		6		7
Amortized Cost	$ 42,104,000		$ 42,104,000		$ 46,969,000
Debt Securities, Available-for-Sale	$ 41,424,000		$ 41,424,000		$ 46,531,000
Investment Securities, Qualitative Disclosure, Number of Positions, Total	11		11		12
Equity Securities [Member]
Equity Securities without Readily Determinable Fair Value, Impairment Loss, Annual Amount			$ 0	0
Common Stock [Member]
Equity Securities Fair Value Gain Loss				$ 5,700,000

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