Represents the amount of equity interest in the investment acquired.

No definition available.

Name:	cmre_HeldtomaturitySecuritiesEquityInterestAcquired
Namespace Prefix:	cmre_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The portion of investment interest rate that accrues quarterly, but payment is deferred until maturity.

+ References

No definition available.

+ Details

Name:	cmre_InvestmentInterestRateStatedPercentageDeferredAccrual
Namespace Prefix:	cmre_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The stated interest rate of an investment.

+ References

No definition available.

+ Details

Name:	cmre_InvestmentStatedInterestRate
Namespace Prefix:	cmre_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Portion of the stated investment interest rate that is payable quarterly.

+ References

No definition available.

+ Details

Name:	cmre_InvestmentStatedInterestRatePayableQuarterly
Namespace Prefix:	cmre_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The write-off of the difference between the aggregate fair value of the debt and equity securities received from ZIM and the then net carrying value of the amounts due from ZIM and is included in General and administrative expenses in the accompanying consolidated statement of income.

+ References

No definition available.

+ Details

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

- Definition

Amount of noncash expense included in interest expense to amortize debt discount and premium associated with the related debt instruments. Excludes amortization of financing costs. Alternate captions include noncash interest expense.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

+ Details

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

- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

+ Details

Name:	us-gaap_EquitySecuritiesFvNi
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

+ Details

Name:	us-gaap_HeldToMaturitySecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of investment in debt security measured at amortized cost (held-to-maturity).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27232-111563

+ Details

Name:	us-gaap_HeldToMaturitySecuritiesFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount by which the fair value of an investment is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 8A
-URI http://asc.fasb.org/extlink&oid=118954083&loc=SL6284422-111562

+ Details

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

- Definition

The amount of other than temporary impairment (OTTI) losses on equity securities, OTTI related to credit losses on debt securities, and OTTI losses on debt securities when the entity intends to sell the securities or it is more likely than not that the entity will be required to sell the securities before recovery of its amortized cost basis. Additionally, this item includes OTTI losses recognized during the period on investments accounted for under the cost method of accounting.

+ References

No definition available.

+ Details

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

- Definition

Dividends received on equity and other investments during the current period.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 16
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3337-108585

+ Details

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

- Definition

The cash inflow associated with the maturity, prepayments and calls (requests for early payments) of debt securities designated as held-to-maturity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3179-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26853-111562

+ Details

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

- Details

Name:	dei_LegalEntityAxis=cmre_ZimIntegratedServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cmre_The3PercentSeries1NotesDue2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=cmre_The5PercentSeries2NotesDue2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	invest_InvestmentAxis=cmre_ZimInvestmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_DebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=cmre_Zim3PercentSeries1NotesDue2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=cmre_Zim5PercentSeries2NotesDue2023Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 4 - Other Non-current Assets (Details Textual) - USD ($) $ in Thousands		6 Months Ended			12 Months Ended	60 Months Ended
	Jul. 16, 2014	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2014	Dec. 31, 2016	Jun. 30, 2019
Amortization of Debt Discount (Premium)		$ (413)	$ (379)
Zim Integrated Services [Member] \| The 3.0% Series 1 Notes Due 2023 [Member]
Investment Stated Interest Rate	3.00%
Zim Integrated Services [Member] \| The 5.0% Series 2 Notes Due 2023 [Member]
Investment Stated Interest Rate	5.00%
Investment Stated Interest Rate, Payable Quarterly	3.00%
Investment Interest Rate, Stated Percentage, Deferred Accrual	2.00%
Zim Investments [Member]
Write-off Deriving from Fair Value Measurement				$ 2,888
Equity Securities [Member] \| Zim Investments [Member]
Held-to-Maturity Securities, Equity Interest Acquired	1.20%
Equity Securities, FV-NI	$ 7,802
Other than Temporary Impairment Losses, Investments, Total		0
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net, Total					$ 4,000
Proceeds from Dividends Received						$ 0
Debt Securities [Member] \| Zim Investments [Member]
Debt Securities, Held-to-maturity, Total	8,229
Debt Securities [Member] \| Zim Investments [Member] \| Zim 3.0% Series 1 Notes Due 2023 [Member]
Debt Securities, Held-to-maturity, Total	1,452				1,406
Debt Securities, Held-to-maturity, Fair Value, Total	676
Proceeds from Maturities, Prepayments and Calls of Held-to-maturity Securities					$ 46
Other than Temporary Impairment Losses, Investments, Total		0
Debt Securities [Member] \| Zim Investments [Member] \| Zim 5.0% Series 2 Notes Due 2023 [Member]
Debt Securities, Held-to-maturity, Total	6,777
Debt Securities, Held-to-maturity, Fair Value, Total	$ 3,567
Amortization of Debt Discount (Premium)		$ 413	$ 379