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CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Parenthetical) - $ / shares | 1 Months Ended
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May 31, 2018 | May 31, 2017
Statement of Stockholders' Equity [Abstract] |  |
Stock dividend issued | 5.00% | 5.00%

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- Definition Percentage of stock dividend issued. + References No definition available. + Details
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Namespace Prefix: | cofs_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration