Note 10 - Long-term Debt - Financing Costs Included in Loan Balances (Details) $ in Thousands	6 Months Ended
Jun. 30, 2017 USD ($)
Balance, January 1, 2017	$ 7,300
Additions	1,147
Amortization	(1,068)
Balance, June 30, 2017	7,379
Less: Current portion of financing costs	(2,087)
Financing costs, non-current portion	$ 5,292

Amount of amortization of deferred financing costs during the period.

No definition available.

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Finance costs that have been incurred and deferred during the period.

No definition available.

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

Amount, after accumulated amortization, of debt and capital lease issuance costs classified as current.

No definition available.

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Namespace Prefix:	cmre_
Data Type:	xbrli:monetaryItemType
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Amount, after accumulated amortization, of debt and capital lease issuance costs classified as noncurrent.

No definition available.

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

Amount, after accumulated amortization, of debt and capital lease issuance costs.

No definition available.

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