Securities Securities - Allowance for Credit Losses on Held to Maturity Securities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Schedule of Held-to-maturity Securities [Line Items]
Securities, held-to-maturity, allowance for credit loss	$ 310		$ 310			$ 310
Debt Securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Securities, held-to-maturity, allowance for credit loss	310	$ 310	310	$ 310	$ 310	$ 310	$ 310	$ 310
Credit loss expense (benefit)	$ 0	$ 0	$ 0	$ 0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

CULLEN/FROST BANKERS, INC. 10-Q