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CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (Parenthetical) - $ / shares	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Statement of Stockholders' Equity [Abstract]
Stock dividend issued	5.00%	5.00%
Cash dividend declared, per share	$ 0.18	$ 0.35

X

- 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

X

- Definition

Aggregate dividends declared during the period for each share of common stock outstanding.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

+ Details

Name:	us-gaap_CommonStockDividendsPerShareDeclared
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
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