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Deposits - Additional Information (Details) - USD ($) $ in Millions | Dec. 31, 2024 | Dec. 31, 2023
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Statistical Disclosure for Banks [Abstract] |  |
Time deposits, $250,000 or more | $ 210.5 | $ 199.7
Interest-bearing and noninterest-bearing deposit, brokered | 36.5 | 23.4
Certificates of deposit issued through CDARS | $ 41.0 | $ 36.2

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- Definition Certificates of deposit issued through the Certificate of Deposit Account Registry Service (CDARS). + References No definition available. + Details
Name: | cofs_CertificatesOfDepositIssuedThroughCDARS
Namespace Prefix: | cofs_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount of interest-bearing and noninterest-bearing third-party deposits placed by or through the assistance of a deposit broker, also known as brokered deposit liabilities. + References No definition available. + Details
Name: | cofs_InterestBearingAndNoninterestBearingDepositBrokered
Namespace Prefix: | cofs_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount of time deposit liabilities, including certificates of deposit, in denominations of $250,000 or more. + References No definition available. + Details
Name: | cofs_TimeDeposits250000OrMore
Namespace Prefix: | cofs_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
Name: | srt_StatisticalDisclosureForBanksAbstract
Namespace Prefix: | srt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration