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Loans and Allowance for Credit Losses - Schedule of Information Regarding Credit Exposure (Parenthetical) (Details) - USD ($) | 6 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2025 | Dec. 31, 2024
Receivables [Abstract] |  |
Financing receivable originated checking accounts writeoffs | $ 266,000 | $ 607,000
Financing receivable originated checking accounts writeoffs annualized | $ 532,000 |

X
- Definition Financing receivable originated checking accounts writeoffs. + References No definition available. + Details
Name: | cofs_FinancingReceivableOriginatedCheckingAccountsWriteoffs
Namespace Prefix: | cofs_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Financing receivable originated checking accounts writeoffs annualized. + References No definition available. + Details
Name: | cofs_FinancingReceivableOriginatedCheckingAccountsWriteoffsAnnualized
Namespace Prefix: | cofs_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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