Income Taxes (Income Tax Computed by Applying U.S. Federal Statutory Income Tax Rate) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount	$ 1,628	$ 1,343	$ 1,527
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent	0.20%	0.20%	0.20%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 0	$ 0	$ 0
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	0.00%	0.00%	0.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Amount	$ (131)	$ (141)	$ (162)
Effective Income Tax Rate Reconciliation, Tax Credit, Percent	0.00%	0.00%	0.00%
Tax-exempt interest	$ (45,497)	$ (38,498)	$ (43,114)
Effective Income Tax Rate Reconciliation, Tax Exempt Income, Percent	(5.90%)	(5.50%)	(6.10%)
FDIC premiums	$ 5,979	$ 5,943	$ 5,263
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent	0.80%	0.90%	0.80%
Executive compensation	$ 2,572	$ 1,629	$ 2,591
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Executive compensation, Percent	0.30%	0.20%	0.40%
Meals and entertainment	$ 2,001	$ 1,861	$ 1,692
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Meals and Entertainment, Percent	0.30%	0.20%	0.20%
Other	$ (925)	$ 1,211	$ 34
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent	(0.10%)	0.20%	0.00%
Tax benefit of 401(k) dividends	$ (2,274)	$ (2,281)	$ (2,135)
Effective Income Tax Rate Reconciliation, Deduction, Employee Stock Ownership Plan Dividend, Percent	(0.30%)	(0.30%)	(0.30%)
Net tax benefit from stock-based compensation	$ (2,265)	$ (3,795)	$ (894)
Effective Income Tax Rate Reconciliation, Tax Expense (Benefit), Share-Based Payment Arrangement, Percent	(0.30%)	(0.60%)	(0.10%)
Income taxes	$ 123,145	$ 113,425	$ 114,400
Effective tax rate	16.00%	16.30%	16.10%
Income Tax Authority, Name [Domain]
Income Tax Disclosure [Abstract]
U.S. federal income tax expense computed at the statutory rate	$ 162,057	$ 146,153	$ 149,598
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%
Effective Income Tax Rate Reconciliation [Line Items]
U.S. federal income tax expense computed at the statutory rate	$ 162,057	$ 146,153	$ 149,598
U.S. federal statutory income tax rate	21.00%	21.00%	21.00%