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Deposits (Details Narrative) - USD ($) $ in Thousands | Dec. 31, 2015 | Dec. 31, 2014
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Deposits [Abstract] |  |
Certificates of deposit $250,000 or greater | $ 21,400 | $ 27,200
Certificates of Deposit issued through CDARS | $ 2,100 | $ 3,100

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

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- Definition Amount of time deposit liabilities, including certificates of deposit, in denominations of $100,000 or more. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Industry Guide -Number 3 -Section V -Paragraph D-E + Details
Name: | us-gaap_TimeDeposits100000OrMore
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant