Loans and Allowance for Credit Losses - Additional Information (Detail) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non Accrual Status Of Loans After Number Of Days Past Due	90 days
Default Status Of TDRs After Number Of Days Past Due	90 days
Charge-offs	$ 5,563,000	$ 1,883,000	$ 33,267,000
Unfunded commitments related to nonperforming loans	200,000		100,000
Off balance sheet reserve to nonperforming loans	0		0
Total gains or losses included in earnings	(6,000)	0
Recorded investment	42,446,000		39,472,000
Loans and Leases Receivable, Gross	8,999,870,000		8,968,761,000
Loans and Leases Receivable, Net of Deferred Income	$ 8,999,870,000		8,968,761,000
Forecasted Value, National Unemployment, Percent	3.79%
Financing Receivable, before Allowance for Credit Loss	$ 8,999,870,000		8,968,761,000
Financing Receivable, Allowance for Credit Loss, Writeoff, after Recovery	4,300,000	1,200,000
Post- Modification Outstanding Recorded Investment	1,715,000	25,000
Financing Receivable, Troubled Debt Restructuring, Subsequent Default	0
Net Deferred Fees
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Deferred Income	9,700,000		8,200,000
Unearned Premiums and Discounts
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Deferred Income	(23,900,000)		(25,700,000)
Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	28,966,000		16,958,000
Financial Asset, Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 8,923,698,000		8,899,737,000
Weighted average [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forecasted Value, National Unemployment, Percent	4.61%
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Forecasted Value, National Unemployment, Percent	4.87%
Time and Demand Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	$ 1,765,000		16,147,000
Loans and Leases Receivable, Gross	1,191,136,000		1,187,300,000
Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	0		0
Loans and Leases Receivable, Gross	575,827,000		551,142,000
Commercial, financial, agricultural and other [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	2,662,000	663,000
Loans and Leases Receivable, Gross	1,593,836,000		1,543,349,000
Loans and Leases Receivable, Net of Deferred Income	1,593,836,000		1,543,349,000
Financing Receivable, before Allowance for Credit Loss	1,593,836,000		1,543,349,000
Post- Modification Outstanding Recorded Investment	1,239,000
Commercial, financial, agricultural and other [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	8,516,000		1,206,000
Commercial, financial, agricultural and other [Member] | Financial Asset, Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,575,009,000		1,527,151,000
Commercial, financial, agricultural and other [Member] | Time and Demand Loans
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	1,765,000	255,000
Loans and Leases Receivable, Gross	1,191,136,000		1,187,300,000
Loans and Leases Receivable, Net of Deferred Income	1,191,136,000		1,187,300,000
Financing Receivable, before Allowance for Credit Loss	1,191,136,000		1,187,300,000
Post- Modification Outstanding Recorded Investment	1,068,000
Commercial, financial, agricultural and other [Member] | Time and Demand Loans | Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	8,013,000		565,000
Commercial, financial, agricultural and other [Member] | Time and Demand Loans | Financial Asset, Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	1,173,733,000		1,172,639,000
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	283,000	0
Loans and Leases Receivable, Gross	3,090,950,000		3,053,152,000
Loans and Leases Receivable, Net of Deferred Income	3,090,950,000		3,053,152,000
Financing Receivable, before Allowance for Credit Loss	3,090,950,000		3,053,152,000
Post- Modification Outstanding Recorded Investment	152,000
Commercial Real Estate [Member] | Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	9,310,000		4,157,000
Commercial Real Estate [Member] | Financial Asset, Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	3,061,404,000		3,028,101,000
Commercial Real Estate [Member] | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Charge-offs	0	0
Loans and Leases Receivable, Gross	575,827,000		551,142,000
Loans and Leases Receivable, Net of Deferred Income	575,827,000		551,142,000
Financing Receivable, before Allowance for Credit Loss	575,827,000		551,142,000
Commercial Real Estate [Member] | Multifamily | Financial Asset, 30 to 59 Days Past Due [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	0		0
Commercial Real Estate [Member] | Multifamily | Financial Asset, Not Past Due
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing Receivable, before Allowance for Credit Loss	$ 575,776,000		551,087,000
Loans to individuals [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Non Accrual Status Of Loans After Number Of Days Past Due	150 days
Nonaccrual Commercial Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Held for sale, Amount	$ 0		$ 0
Loans and Leases Receivable, Gain (Loss) on Sales, Net	$ 0	$ 0