Capital Leased Assets and Capital Lease Obligations (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Prepaid lease rentals [Abstract]:
Prepaid lease rentals	$ 40,811	$ 45,793
Additions	26,390	0	$ 49,817
Less: Amortization of prepaid lease rentals	(6,779)	(4,982)	$ (4,024)
Prepaid lease rentals	60,422	40,811
Less: Current portion of financing costs	(8,752)	(4,982)
Non-current portion	$ 51,670	$ 35,829

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

No definition available.

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- Definition

The expense charged against prepaid lease rentals over the lease term.

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No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

It is the current portion of the unamortized balance of the difference between the fair value of the asset sold and the carrying amount of the asset, when the fair value of the asset sold is more than its carrying amount. It is also include the amount of net settlement of interest rate swaps qualifying for cash flow hedge that has been reclassified as prepaid lease rentals. The prepaid lease rental is amortizing over the lease term.

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No definition available.

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

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No definition available.

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- Definition

The amount before depreciation/ amortization of the difference between the fair value of the asset sold and the carrying amount of the asset, when the fair value of the asset sold is more than its carrying amount and the amount of net settlement of interest rate swaps qualifying for cash flow hedge that has been reclassified as prepaid lease rentals. The prepaid lease rental is amortizing over the lease term.

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No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- Definition

The amount after depreciation of the difference between the fair value of the asset sold and the carrying amount of the asset, when the fair value of the asset sold is more than its carrying amount and the amount of net settlement of interest rate swaps qualifying for cash flow hedge that has been reclassified as prepaid lease rentals. The prepaid lease rental is amortizing over the lease term.

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No definition available.

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Balance Type:	debit
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- Definition

It is the non-current portion of the unamortized balance of the difference between the fair value of the asset sold and the carrying amount of the asset, when the fair value of the asset sold is more than its carrying amount. It is also include the amount of net settlement of interest rate swaps qualifying for cash flow hedge that has been reclassified as prepaid lease rentals. The prepaid lease rental is amortizing over the lease term.

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No definition available.

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Period Type:	instant