Percentage of allowance for credit losses.

No definition available.

Name:	cofs_PercentageOfAllowanceForCreditLosses
Namespace Prefix:	cofs_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of increase decrease of loans and leases receivable.

+ References

No definition available.

+ Details

Name:	cofs_PercentageOfIncreaseDecreaseOfLoansAndLeasesReceivable
Namespace Prefix:	cofs_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of loan s and leases receivable.

+ References

No definition available.

+ Details

Name:	cofs_PercentageOfLoanSAndLeasesReceivable
Namespace Prefix:	cofs_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481696/310-30-50-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-SubTopic 10
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-11B

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 11B
-Subparagraph (g)
-SubTopic 10
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481962/310-10-50-11B

Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-SubTopic 10
-Topic 310
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480418/310-10-S99-4

+ Details

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

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

+ Details

Name:	us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount after allowance and deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements and loans held for sale.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481990/310-10-45-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

+ Details

Name:	us-gaap_LoansAndLeasesReceivableNetReportedAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=cofs_AgriculturalMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=cofs_CommercialAndIndustrialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=cofs_ConstructionRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=cofs_LoansToOtherFinancialInstitutionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans and Allowance for Credit Losses - Loans by Type as Percentage of Portfolio (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2024	Dec. 31, 2023	Mar. 31, 2024	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (Note 3)	$ 1,437,527	$ 1,410,653
Allowance for loan losses (Note 3)	$ 16,152	$ 15,685	$ 16,037	$ 14,582	$ 15,065	$ 7,619
Percentage of allowance for credit losses	1.12%	1.11%
Loans, net	$ 1,421,375	$ 1,394,968
Agricultural [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (Note 3)	$ 45,274	$ 49,210
Percentage of loans	3.20%	3.50%
Percentage of increase decrease of loans	(8.00%)
Allowance for loan losses (Note 3)	$ 112	$ 94	97	78	136	144
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (Note 3)	$ 224,031	$ 229,915
Percentage of loans	15.60%	16.30%
Percentage of increase decrease of loans	(2.60%)
Allowance for loan losses (Note 3)	$ 2,161	$ 2,216	2,243	2,896	3,020	1,361
Commercial Real Estate Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (Note 3)	$ 804,213	$ 786,921
Percentage of loans	55.90%	55.80%
Percentage of increase decrease of loans	2.20%
Allowance for loan losses (Note 3)	$ 9,361	$ 8,820	9,167	7,237	7,837	4,822
Consumer Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (Note 3)	$ 32,811	$ 36,541
Percentage of loans	2.30%	2.60%
Percentage of increase decrease of loans	(10.20%)
Allowance for loan losses (Note 3)	$ 795	$ 823	918	885	913	310
Construction Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (Note 3)	$ 18,751	$ 20,936
Percentage of loans	1.30%	1.50%
Percentage of increase decrease of loans	(10.40%)
Allowance for loan losses (Note 3)	$ 49	$ 58	49	70	72	63
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (Note 3)	$ 275,878	$ 267,730
Percentage of loans	19.20%	19.00%
Percentage of increase decrease of loans	3.00%
Allowance for loan losses (Note 3)	$ 3,624	$ 3,644	3,513	3,376	3,087	906
Loans To Other Financial Institutions [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans (Note 3)	$ 36,569	$ 19,400
Percentage of loans	2.50%	1.40%
Percentage of increase decrease of loans	88.50%
Allowance for loan losses (Note 3)	$ 50	$ 30	$ 50	$ 40	$ 0	$ 0