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Fair Value Measurements - Additional Information (Detail) - USD ($) $ in Thousands | Jun. 30, 2021 | Dec. 31, 2020
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Financial instruments using fair value measurement option | $ 0 | $ 0

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- Definition Financial instruments using fair value measurement option + References No definition available. + Details
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Namespace Prefix: | cfr_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition 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. + References No definition available. + Details
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration