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Deposits (Details Narrative) - USD ($) $ in Thousands | Dec. 31, 2018 | Dec. 31, 2017
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Deposits [Abstract] |  |
Certificates of deposit $250,000 or greater | $ 39,300 | $ 29,800
Brokered certificates of deposit | 34,370 | 10,172
Certificates of Deposit issued through CDARS | $ 2,100 | $ 2,000

X
- 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

X
- Definition Refers to the information relating to interest bearing domestic deposit brokered certificates of deposits. + References No definition available. + Details
Name: | cofs_InterestBearingDomesticDepositBrokeredCertificatesOfDeposits
Namespace Prefix: | cofs_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- 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

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