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Deposits (Details Narrative) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deposits [Abstract]
Certificates of deposit $250,000 or greater	$ 68,300	$ 39,300
Brokered certificates of deposit	2,300	34,400
Certificates of Deposit issued through CDARS	$ 7,100	$ 2,100

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

Amount refers to the interest bearing domestic deposit brokered certificates of deposits.

+ References

No definition available.

+ Details

Name:	cofs_InterestBearingDomesticDepositBrokeredCertificatesOfDeposits1
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