Off-Balance Sheet Arrangements Commitments Guarantees and Contingencies (Narrative) (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Commitments And Guarantees [Line Items]
Off-Balance-Sheet, Credit Loss, Liability, Change in Method, Credit Loss Expense (Reversal)		$ 1,800
Credit card guarantees	$ 4,800	4,900
Fully collateralized credit card guarantees	593	673
Consumer Loan [Member]
Commitments And Guarantees [Line Items]
Off-Balance-Sheet, Credit Loss, Liability, Change in Method, Credit Loss Expense (Reversal)		1,600
Commercial mortgage [Member]
Commitments And Guarantees [Line Items]
Off-Balance-Sheet, Credit Loss, Liability, Change in Method, Credit Loss Expense (Reversal)		211
Frost Wealth Advisors [Member]
Commitments And Guarantees [Line Items]
Fair value of off-balance sheet managed and custody assets	$ 51,000,000	$ 51,400,000	$ 47,200,000