Name:	cofs_FederalHomeLoanBankAdvancesDueDate
Namespace Prefix:	cofs_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

Discloses the call date for the advances from the Federal Home Loan Bank, as of the Balance Sheet date.

No definition available.

Name:	cofs_FederalHomeLoanBankAdvancesDueDateEarliest
Namespace Prefix:	cofs_
Data Type:	xbrli:gYearMonthItemType
Balance Type:	na
Period Type:	duration

Amount of borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages.

Name:	us-gaap_AdvancesFromFederalHomeLoanBanks
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Discloses the single interest rate [if] applicable to the advances from the Federal Home Loan Bank, by branch, as of the Balance Sheet date.

Name:	us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Discloses the lowest interest rate applicable to any of the advances from the Federal Home Loan Bank, by branch, as of the Balance Sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.13(3)(a))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Name:	us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRateRangeFrom
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Discloses the highest interest rate applicable to any of the advances from the Federal Home Loan Bank, by branch, as of the Balance Sheet date.

Name:	us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankInterestRateRangeTo
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

Describes the weighted average interest rate applicable to the specific advances from the Federal Home Loan Bank, by branch, as of the Balance Sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 470

-Section 50

-Paragraph 3

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682