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Note 14 - Employee Benefit Plans (Details Textual) - USD ($) | 12 Months Ended
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Dec. 31, 2022 | Dec. 31, 2021
The 401(k) Plan [Member] |  |
Defined Contribution Plan, Cost | $ 650,000 | $ 627,000

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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
Name: | us-gaap_DefinedContributionPlanCostRecognized
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_RetirementPlanNameAxis=cofs_The401kPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |