Note 20 - Earnings (Loss) Per Common Share (Details Textual)	9 Months Ended
Sep. 30, 2021
Redeemable Non-controlling Interest Membership Units Not Held Share Ratio	10

Represents redeemable non-controlling interest membership units not held share ratio.

No definition available.

Name:	cohn_RedeemableNoncontrollingInterestMembershipUnitsNotHeldShareRatio
Namespace Prefix:	cohn_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration