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

X

- Definition

Percentage of stock dividend issued.

+ References

No definition available.

+ Details

Name:	cofs_StockDividendIssued
Namespace Prefix:	cofs_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

Name:	us-gaap_StatementOfStockholdersEquityAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration