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v3.23.1

Loans by Type (Details) - TDRs $ in Thousands | Mar. 31, 2023 USD ($)
--- | ---
Financing Receivable, Past Due [Line Items] |
Modified loans | $ 0
Commercial and industrial |
Financing Receivable, Past Due [Line Items] |
Modified loans | 0
Current |
Financing Receivable, Past Due [Line Items] |
Modified loans | 11,225
Current | Commercial and industrial |
Financing Receivable, Past Due [Line Items] |
Modified loans | 11,225
30-59 Days |
Financing Receivable, Past Due [Line Items] |
Modified loans | 0
30-59 Days | Commercial and industrial |
Financing Receivable, Past Due [Line Items] |
Modified loans | 0
60-89 Days |
Financing Receivable, Past Due [Line Items] |
Modified loans | 0
60-89 Days | Commercial and industrial |
Financing Receivable, Past Due [Line Items] |
Modified loans | 0
90 Days and Over |
Financing Receivable, Past Due [Line Items] |
Modified loans | 0
90 Days and Over | Commercial and industrial |
Financing Receivable, Past Due [Line Items] |
Modified loans | $ 0

X
- Definition Financing Receivable, Excluding Accrued Interest, Modified, after 12 Months + References No definition available. + Details
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Namespace Prefix: | cass_
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
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_FinancingReceivablesPeriodPastDueAxis=us-gaap_FinancialAssetNotPastDueMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |