The amount of annual return on investment due to related parties.

No definition available.

Name:	cohn_DueToRelatedPartiesAnnualReturnOnInvestment
Namespace Prefix:	cohn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of annual return on investment is revenue is zero or less due to related parties.

+ References

No definition available.

+ Details

Name:	cohn_DueToRelatedPartiesAnnualReturnOnInvestmentIfRevenueIsZeroOrLess
Namespace Prefix:	cohn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of annual return on revenue of the business of investment by related party.

+ References

No definition available.

+ Details

Name:	cohn_DueToRelatedPartiesAnnualReturnOnRevenueOfBusinessAmount
Namespace Prefix:	cohn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The annual revenue of the business return on investment from related parties.

+ References

No definition available.

+ Details

Name:	cohn_DueToRelatedPartiesAnnualRevenueOfTheBusinessReturn
Namespace Prefix:	cohn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The alternative period of required written notice contingency under the investment agreement.

+ References

No definition available.

+ Details

Name:	cohn_InvestmentAgreementAlternativePeriodOfRequiredPriorWrittenNoticeContingency
Namespace Prefix:	cohn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of investment return on the business revenues when revenues of the business are greater than zero.

+ References

No definition available.

+ Details

Name:	cohn_InvestmentAgreementPercentageOfInvestmentReturnOnBusinessRevenueForRevenuesGreaterThanZero
Namespace Prefix:	cohn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of investment return on the investment amount when revenues of the business are greater than zero.

+ References

No definition available.

+ Details

Name:	cohn_InvestmentAgreementPercentageOfInvestmentReturnOnInvestmentAmountForRevenuesGreaterThanZero
Namespace Prefix:	cohn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of investment return on the investment amount when revenues of the business are zero or less than zero.

+ References

No definition available.

+ Details

Name:	cohn_InvestmentAgreementPercentageOfInvestmentReturnOnInvestmentAmountForRevenuesWithZeroOrLessThanZero
Namespace Prefix:	cohn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of consideration on qualified sale owed to the investor under the investment agreement.

+ References

No definition available.

+ Details

Name:	cohn_InvestmentAgreementPotentialConsiderationToInvestorPercentageOnQualifiedSale
Namespace Prefix:	cohn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The total amount of funded operating costs that must be repaid from revenue before quarterly payments from revenue can be made under the investment agreement.

+ References

No definition available.

+ Details

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

- Definition

The written notice period for termination under the investment agreement.

+ References

No definition available.

+ Details

Name:	cohn_InvestmentAgreementWrittenNoticePeriodForTermination
Namespace Prefix:	cohn_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of cash outflow for redeemable financial instruments.

+ References

No definition available.

+ Details

Name:	cohn_PaymentsForRedeemableFinancialInstruments
Namespace Prefix:	cohn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of cash outflow to subsidiary for investment.

+ References

No definition available.

+ Details

Name:	cohn_PaymentsToSubsidiaryInvestment
Namespace Prefix:	cohn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amount of cash inflow for redeemable financial instruments.

+ References

No definition available.

+ Details

Name:	cohn_ProceedsFromRedeemableFinancialInstruments
Namespace Prefix:	cohn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of redeemable financial instruments.

+ References

No definition available.

+ Details

Name:	cohn_RedeemableFinancialInstruments
Namespace Prefix:	cohn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of cash outflow for redeemable financial instruments.

+ References

No definition available.

+ Details

Name:	cohn_RepaymentsOfRedeemableFinancialInstruments
Namespace Prefix:	cohn_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of obligations due all related parties.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(k)(1))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.17)
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.15(3),(4))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

+ Details

Name:	us-gaap_DueToRelatedPartiesCurrentAndNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=cohn_InvestmentAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_OwnershipAxis=cohn_VianovaCapitalGroupLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=cohn_JkdCapitalPartnersILtdMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=cohn_DgcFamilyFintechTrustcbfMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=cohn_CBFMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=cohn_RevenueBetweenZeroAnd11777ThousandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=cohn_RevenueInExcessOf11777ThousandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=cohn_RevenueBetweenZeroAnd5333ThousandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=cohn_RevenueBetween5333ThousandAnd8000ThousandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementScenarioAxis=cohn_RevenueInExcessOf8000ThousandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=cohn_DGCTrustMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=cohn_HancockFundingLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=cohn_NewAvenueInvestmentsLlcMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=cohn_JvbHoldingsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 19 - Redeemable Financial Instruments (Details Textual) - USD ($)							1 Months Ended
	Oct. 15, 2020	Sep. 30, 2020	Mar. 06, 2019	Jan. 09, 2019	Nov. 19, 2018	Oct. 03, 2016	Oct. 31, 2019	Feb. 28, 2019	Jan. 31, 2017	Dec. 31, 2020	Sep. 29, 2020	Sep. 25, 2020	Dec. 31, 2019	Dec. 31, 2018	Sep. 29, 2017
Redeemable Financial Instruments										$ 11,957,000			$ 16,983,000
Investment Agreement [Member]
Investment Agreement, Repayment of Funded Operating Costs Before Quarterly Payments					$ 693,000
Investment Agreement [Member] \| ViaNova Capital Group, LLC [Member]
Payments to Subsidiary, Investment					500,000
JKD Capital Partners I, LTD [Member]
Redeemable Financial Instruments										7,957,000			$ 7,957,000
JKD Capital Partners I, LTD [Member] \| Investment Agreement [Member]
Redeemable Financial Instruments						$ 12,000,000
Proceeds from Redeemable Financial Instruments				$ 1,268,000		$ 6,000,000			$ 1,000,000
Due to Related Parties, Annual Return on Investment						50.00%
Due to Related Parties, Annual Revenue of the Business Return														42.00%
Investment Agreement, Written Notice Period for Termination (Day)			90 days
Investment Agreement, Alternative Period of Required Prior Written Notice Contingency (Day)			60 days
Investment Agreement, Potential Consideration to Investor, Percentage on Qualified Sale			25.00%
DGC Family Fintech Trust/CBF [Member]
Redeemable Financial Instruments										$ 8,000,000
CBF [Member] \| Investment Agreement [Member]
Redeemable Financial Instruments	$ 4,000,000											$ 6,500,000			$ 8,000,000
Due to Related Parties, Annual Return on Investment										20.00%	3.75%
Due to Related Parties, Annual Revenue of the Business Return											15.29%
Due to Related Parties, Total							$ 6,500,000
Repayments of Redeemable Financial Instruments							$ 1,500,000
Due to Related Parties, Annual Return on Investment if Revenue is Zero or Less											3.75%
Payments for Redeemable Financial Instruments	$ 2,500,000
Investment Agreement, Percentage of Investment Return on Investment Amount for Revenues Greater than Zero	20.00%									20.00%
Investment Agreement, Percentage of Investment Return on Business Revenue for Revenues Greater than Zero	9.40%									15.20%
Investment Agreement, Percentage of Investment Return on Investment Amount for Revenues with Zero or Less than Zero	3.75%									3.75%
CBF [Member] \| Investment Agreement [Member] \| Revenue Between Zero and $11,777 Thousand [Member]
Due to Related Parties, Annual Revenue of the Business Return											11.47%
CBF [Member] \| Investment Agreement [Member] \| Revenue in Excess of $11,777 Thousand [Member]
Due to Related Parties, Annual Revenue of the Business Return											7.65%
CBF [Member] \| Investment Agreement [Member] \| Revenue Between Zero and $5,333 Thousand [Member]
Due to Related Parties, Annual Revenue of the Business Return											11.47%
CBF [Member] \| Investment Agreement [Member] \| Revenue Between $5,333 Thousand and $8,000 Thousand [Member]
Due to Related Parties, Annual Return on Revenue of Business, Amount											$ 612,000
CBF [Member] \| Investment Agreement [Member] \| Revenue in Excess of $8,000 Thousand [Member]
Due to Related Parties, Annual Revenue of the Business Return											7.65%
DGC Trust [Member]
Redeemable Financial Instruments		$ 2,000,000
DGC Trust [Member] \| Investment Agreement [Member]
Redeemable Financial Instruments												$ 2,000,000			$ 2,000,000
Due to Related Parties, Annual Return on Investment										20.00%	3.75%
Due to Related Parties, Annual Revenue of the Business Return											4.71%
Due to Related Parties, Annual Return on Investment if Revenue is Zero or Less										3.75%
Payments for Redeemable Financial Instruments		$ 2,000,000
DGC Trust [Member] \| Investment Agreement [Member] \| Revenue Between Zero and $11,777 Thousand [Member]
Due to Related Parties, Annual Revenue of the Business Return											3.53%
DGC Trust [Member] \| Investment Agreement [Member] \| Revenue in Excess of $11,777 Thousand [Member]
Due to Related Parties, Annual Revenue of the Business Return											2.35%
DGC Trust [Member] \| Investment Agreement [Member] \| Revenue Between Zero and $5,333 Thousand [Member]
Due to Related Parties, Annual Revenue of the Business Return											3.53%
DGC Trust [Member] \| Investment Agreement [Member] \| Revenue Between $5,333 Thousand and $8,000 Thousand [Member]
Due to Related Parties, Annual Return on Revenue of Business, Amount											$ 188,000
DGC Trust [Member] \| Investment Agreement [Member] \| Revenue in Excess of $8,000 Thousand [Member]
Due to Related Parties, Annual Revenue of the Business Return											2.35%
Hancock Funding, LLC [Member] \| Investment Agreement [Member]
Redeemable Financial Instruments					500,000
New Avenue Investments LLC [Member] \| Investment Agreement [Member]
Redeemable Financial Instruments					250,000
Proceeds from Redeemable Financial Instruments								$ 220,000
JVB Holdings [Member] \| Investment Agreement [Member]
Redeemable Financial Instruments					$ 2,750,000