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

No definition available.

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

- Definition

Portion of the stated interest rate that is payable quarterly.

+ References

No definition available.

+ Details

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

- Definition

Amount recorded in relation to the equity and debt securities fair value unwinding, which is included in the interest income in the consolidated statement of income for the reporting period.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of equity interest in the investment acquired.

+ References

No definition available.

+ Details

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

- 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

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of distribution received from equity method investee for return on investment, classified as operating activities. Excludes distribution for return of investment, classified as investing activities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-04(10))
-URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03(12))
-URI http://asc.fasb.org/extlink&oid=63488584&loc=d3e20235-122688

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 21D
-URI http://asc.fasb.org/extlink&oid=98514028&loc=SL94080555-108585

+ Details

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

- Definition

Amount after other than temporary impairment (OTTI) accretion, of investments in debt securities classified as held-to-maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 25
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=75030427&loc=d3e22054-111558

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27232-111563

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.6)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Fair value of investments in debt securities classified as held-to-maturity.

+ References

+ Details

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

- 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

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-URI http://asc.fasb.org/extlink&oid=82897076&loc=SL6284393-111563

+ Details

Name:	us-gaap_OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNet
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://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=82896770&loc=d3e26853-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3179-108585

+ 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_MajorTypesOfDebtAndEquitySecuritiesAxis=us-gaap_EquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_DebtSecurityAxis=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	36 Months Ended
	Jul. 16, 2014	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2014	Dec. 31, 2016	Jun. 30, 2017
Proceeds from Equity Method Investment, Distribution		$ 270	$ 0
Zim Integrated Services [Member] \| The 3.0% Series 1 Notes Due 2023 [Member]
Debt Instrument, Interest Rate, Stated Percentage	3.00%
Zim Integrated Services [Member] \| The 5.0% Series 2 Notes Due 2023 [Member]
Debt Instrument, Interest Rate, Stated Percentage	5.00%
Debt Instrument, Interest Rate, Stated Percentage, Payable Quarterly	3.00%
Debt Instrument, Interest Rate, Stated Percentage, Deferred Accrual	2.00%
Zim Investments [Member]
Write-off Deriving from Fair Value Measurement				$ 2,888
Fair Value Unwinding		348	$ 321
Equity Securities [Member] \| Zim Investments [Member]
Held-to-Maturity Securities, Equity Interest Acquired	1.20%
Held-to-maturity Securities, Fair Value	$ 7,802
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net		0			$ 4,000
Proceeds from Equity Method Investment, Distribution						$ 0
Debt Securities [Member] \| Zim Investments [Member]
Held-to-maturity Securities	8,229
Debt Securities [Member] \| Zim Investments [Member] \| Zim 3.0% Series 1 Notes Due 2023 [Member]
Proceeds from Maturities, Prepayments and Calls of Held-to-maturity Securities					46
Held-to-maturity Securities	1,452				$ 1,406
Held-to-maturity Securities, Fair Value	676
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net		0
Debt Securities [Member] \| Zim Investments [Member] \| Zim 5.0% Series 2 Notes Due 2023 [Member]
Held-to-maturity Securities	6,777
Held-to-maturity Securities, Fair Value	$ 3,567
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net		$ 0