Amounts transferred to Prepaid lease rentals at the inception of the capital lease transactions.

No definition available.

Name:	cmre_AdditionsOfPrepaidLeaseRentals
Namespace Prefix:	cmre_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Capital leased assets value at the inception of the capital lease transactions

+ References

No definition available.

+ Details

Name:	cmre_AdditionsToCapitalLeasedAssets
Namespace Prefix:	cmre_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amounts transferred to unearned revenue during the reporting period.

+ References

No definition available.

+ Details

Name:	cmre_AdditionsToUnearnedRevenue
Namespace Prefix:	cmre_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The amounts reclassified from Net settlements on interest rate swaps qualifying for hedge accounting to Prepaid lease rentals

+ References

No definition available.

+ Details

Name:	cmre_AmountsReclassifiedFromNetSettlementsOnInterestRateSwapsQualifyingForHedgeAccountingToPrepaidLeaseRentals
Namespace Prefix:	cmre_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount after accumulated depreciation of leased physical assets used in the normal conduct of business to produce goods and services.

+ References

No definition available.

+ Details

Name:	cmre_FinanceLeasedAssetsNet
Namespace Prefix:	cmre_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The term of the sale of the property to another party and the lease of the property back to the seller.

+ References

No definition available.

+ Details

Name:	cmre_SaleLeasebackTransactionTerm
Namespace Prefix:	cmre_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The per vessel price for the 3 vessels (MSC Azov, MSC Ajaccio and MSC Amalfi), due to the sale and leaseback transaction.

+ References

No definition available.

+ Details

Name:	cmre_VesselsSaleAndLeasebackPrice
Namespace Prefix:	cmre_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The expense charged against earnings for the periodic recognition of capitalized leases. This element may apply to energy companies that lease mineral producing properties and to other enterprises that capitalize property, plant, or equipment obtained through capital leases.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=84164758&loc=d3e45031-112735

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-Publisher FASB
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-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

+ Details

Name:	us-gaap_AmortizationOfLeasedAsset
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of minimum lease payments for capital leases net of executory costs, which include amounts paid by the lessee to the lessor for insurance, maintenance and taxes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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+ Details

Name:	us-gaap_CapitalLeasesFutureMinimumPaymentsNetMinimumPayments1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The financing charge for leasing arrangements meeting the criteria for capitalization.

+ References

+ Details

Name:	us-gaap_CapitalLeasesIncomeStatementInterestExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The accumulated depreciation and amortization related to the asset(s) sold in connection with the property sold to another party and leased back to the seller.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 40
-Section 55
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+ Details

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

- Details

Name:	us-gaap_SaleLeasebackTransactionDescriptionAxis=cmre_SaleLeasebackTransactionsRegardingTheVesselsMscAzovMscAjaccioAndMscAmalfiMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SaleLeasebackTransactionDescriptionAxis=cmre_SaleLeasebackTransactionsRegardingTheVesselMSCAthosMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SaleLeasebackTransactionDescriptionAxis=cmre_SaleLeasebackTransactionsRegardingTheVesselLeonidioMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
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Period Type:

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Namespace Prefix:
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Note 11 - Capital Leased Assets and Capital Lease Obligations (Details Textual) - USD ($) $ in Thousands				4 Months Ended	6 Months Ended		12 Months Ended
	Jun. 19, 2017	Jul. 15, 2016	Jun. 06, 2016	Apr. 30, 2014	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Amounts Reclassified From Net Settlements On Interest Rate Swaps Qualifying For Hedge Accounting To Prepaid Lease Rentals							$ 1,076
Additions to Unearned Revenue					$ 4,481
Additions To Capital Leased Assets					452,564
Amortization of Leased Asset					6,269	$ 3,770
Sale Leaseback Transaction, Accumulated Depreciation					29,961		23,692
Finance Leased Assets, Net					422,603		384,872
Capital Leases, Future Minimum Payments, Net Minimum Payments					392,959
Capital Leases, Income Statement, Interest Expense					10,538	$ 8,177
Additions Of Prepaid Lease Rentals							$ 26,390
Sale Leaseback Transactions Regarding the Vessels MSC Azov, MSC Ajaccio and MSC Amalfi [Member]
Vessel's sale and leaseback price				$ 85,572
Sale Leaseback Transaction, Term				10 years
Sale Leaseback Transactions Regarding the Vessel MSC Athos [Member]
Sale Leaseback Transaction, Term			7 years
Sale Leaseback Transactions Regarding the Vessel Leonidio [Member]
Sale Leaseback Transaction, Term	7 years
Sale Leaseback Transactions Regarding the Vessel MSC Athens [Member]
Sale Leaseback Transaction, Term		7 years
Sale Leaseback Transactions Regarding the Vessel Kyparissia [Member]
Sale Leaseback Transaction, Term	7 years