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v3.20.1

Off-Balance Sheet Activities (Details Narrative) | 12 Months Ended
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Dec. 31, 2019
Lower Range [Member] |
Interest rate of commitments | 3.25%
Term of commitments | 1 year
Upper Range [Member] |
Interest rate of commitments | 7.50%
Term of commitments | 30 years

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- Definition The interest rate for commitments to extend credit. + References No definition available. + Details
Name: | cofs_InterestRateCommitmentsToExtendCredit
Namespace Prefix: | cofs_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition The maturity term of commitments to extend credit. + References No definition available. + Details
Name: | cofs_TermCommitmentsToExtendCredit
Namespace Prefix: | cofs_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |