Account transaction between trade date and settlement date as a derivative as either a forward purchase commitment or a forward sale commitment due to financial instrument not settling within regular time frame.

No definition available.

+ Details

Name:	cohn_ForwardPurchaseCommitment
Namespace Prefix:	cohn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

+ References

No definition available.

+ Details

Name:	cohn_ForwardSaleCommitment
Namespace Prefix:	cohn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cohn_TbaAndOtherForwardAgencyMbsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PositionAxis=us-gaap_ShortMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PositionAxis=us-gaap_LongMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeForwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_OtherContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cohn_TbaAndOtherForwardAgencyMbsPurchaseAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=cohn_TbaAndOtherForwardMbsSaleAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Derivative Financial Instruments (Narrative) (Details) - USD ($)	Apr. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
TBA And Other Forward Agency MBS [Member] \| Short [Member]
Derivative [Line Items]
Derivative, Notional Amount		$ 2,212,275,000	$ 1,874,194,000
TBA And Other Forward Agency MBS [Member] \| Long [Member]
Derivative [Line Items]
Derivative, Notional Amount		2,090,750,000	1,773,000,000
Foreign currency forward contracts [Member]
Derivative [Line Items]
Derivative, Notional Amount		0		$ 0
Other Extended Settlement Trades [Member]
Derivative [Line Items]
Forward purchase commitment		1,725,000	1,526,000
Forward sale commitment		$ 0	$ 0
Subsequent Event [Member] \| TBA And Other Forward Agency MBS Purchase Agreements [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 1,134,419,000
Subsequent Event [Member] \| TBA And Other Forward MBS Sale Agreements [Member]
Derivative [Line Items]
Derivative, Notional Amount	$ 1,252,919,000