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Note 12 - Investments in Equity Method Affiliates (Details Textual) - SPAC Sponsor Entities [Member]	12 Months Ended
	Dec. 31, 2020 shares
Equity Method Investment, Shares Purchased (in shares)	765,000
Equity Method Investment, Shares Received (in shares)	1,074,000

X

- Definition

The number of shares received upon purchase of investment accounted for under the equity method of accounting.

+ References

No definition available.

+ Details

Name:	cohn_EquityMethodInvestmentSharesPurchased
Namespace Prefix:	cohn_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Represents shares received from equity method method investment.

+ References

No definition available.

+ Details

Name:	cohn_EquityMethodInvestmentSharesReceived
Namespace Prefix:	cohn_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

X

- Details

Name:	us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeAxis=cohn_SPACSponsorEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: