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Loans and Allowance for Credit Losses - Schedule of Information Regarding Credit Exposure (Parenthetical) (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Receivables [Abstract]
Financing receivable originated checking accounts writeoffs	$ 440,000	$ 607,000
Financing receivable originated checking accounts writeoffs annualized	$ 587,000

X

- Definition

Financing receivable originated checking accounts writeoffs.

+ References

No definition available.

+ Details

Name:	cofs_FinancingReceivableOriginatedCheckingAccountsWriteoffs
Namespace Prefix:	cofs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Definition

Financing receivable originated checking accounts writeoffs annualized.

+ References

No definition available.

+ Details

Name:	cofs_FinancingReceivableOriginatedCheckingAccountsWriteoffsAnnualized
Namespace Prefix:	cofs_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- References

No definition available.

+ Details

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