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Note 2 - Basis of Presentation (Details Textual) | 12 Months Ended
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Dec. 31, 2018 USD ($)
Increase in Reverse Repurchase Agreement and Repurchase Agreement Amounts [Member] |
Prior Period Reclassification Adjustment | $ 2,461,177

X
- Definition The amount of a reclassification adjustment made to prior period financial statement amounts. + References No definition available. + Details
Name: | us-gaap_PriorPeriodReclassificationAdjustment
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_AdjustmentsForChangeInAccountingPrincipleAxis=cohn_IncreaseInReverseRepurchaseAgreementAndRepurchaseAgreementAmountsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |