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Note 10 - Borrowings - Federal Home Loan Bank Advances (Details) - USD ($) $ in Thousands | Dec. 31, 2022 | Dec. 31, 2021
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Federal Home Loan Bank Advances Maturing January 2023 [Member] |  |
Total advances outstanding at year-end | $ 50,000 | $ 0
Federal Home Loan Bank Advances Maturing January 2022 [Member] |  |
Total advances outstanding at year-end | 0 | 50,000
Federal Home Loan Bank Advances [Member] |  |
Total advances outstanding at year-end | $ 50,000 | $ 50,000

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- Definition Amount of borrowings as of the balance sheet date from the Federal Home Loan Bank, which are primarily used to cover shortages in the required reserve balance and liquidity shortages. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 45 -Paragraph 1 -URI https://asc.fasb.org/extlink&oid=6479118&loc=d3e64650-112822 + Details
Name: | us-gaap_AdvancesFromFederalHomeLoanBanks
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Details
Name: | us-gaap_LongtermDebtTypeAxis=cofs_FederalHomeLoanBankAdvancesMaturingJanuary2023Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_LongtermDebtTypeAxis=cofs_FederalHomeLoanBankAdvancesMaturingJanuary2022Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_LongtermDebtTypeAxis=us-gaap_FederalHomeLoanBankAdvancesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |