Business acquisition number of shares received upon conversion.

No definition available.

Name:	cofs_BusinessAcquisitionNumberOfSharesReceivedUponConversion
Namespace Prefix:	cofs_
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Balance Type:	na
Period Type:	instant

- Definition

Sale of Interest Rate Swaps.

+ References

No definition available.

+ Details

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

- Definition

With respect to a business combination completed during the period, this element provides a description of the business, other than the name, which may include the industry, size, products and other important information.

+ References

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-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
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+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

+ References

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

+ References

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-Section 50
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+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	instant

- Definition

Period remaining until the derivative contract matures, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Fixed interest rate that will be received or paid upon exercise of the interest rate swaption contract.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

+ References

No definition available.

+ Details

Name:	us-gaap_SaleOfStockPricePerShare
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:perShareItemType
Balance Type:	na
Period Type:	instant

- Definition

Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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Period Type:	duration

- Definition

The net change in the difference between the fair value and the carrying value, or in the comparative fair values, of derivative instruments, including options, swaps, futures, and forward contracts, held at each balance sheet date, that was included in earnings for the period.

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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Period Type:

Subsequent Events - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions			12 Months Ended
	Feb. 28, 2025	Feb. 06, 2025	Dec. 31, 2024	Dec. 31, 2023
Subsequent Event [Line Items]
Common stock, outstanding (in shares)			8,965,483	7,548,217
ChoiceOne [Member]
Subsequent Event [Line Items]
Business acquisition description			On March 1, 2025, ChoiceOne Financial Services, Inc. ("ChoiceOne") completed its merger with Fentura Financial, Inc. ("Fentura"), with ChoiceOne continuing as the surviving corporation. The combined organization will be headquartered in Sparta, Michigan, and will operate under the ChoiceOne name and brand.
Subsequent Event \| Interest rate swaps
Subsequent Event [Line Items]
Sale of interest rate swaps		$ 50.0
Fixed rate swaps		2.75%
Gain on transaction		$ 3.6
Remaining on the life of the swap		7 years
Subsequent Event \| Merger Agreement \| Fentura Financial, Inc. [Member]
Subsequent Event [Line Items]
Number of shares each share of Fentura common stock outstanding will be converted into (in shares)	1.35
Common stock, outstanding (in shares)	4,497,069
Closing stock price	$ 31.79
Transaction value	$ 193.0