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

Amount billed to customers under long-term contracts or programs but not paid. Excludes amounts due that have been withheld because of retainage provisions in a contract.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 910
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482546/910-10-50-6

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

Amount of right to consideration in exchange for good or service transferred to customer under long-term contract or program when right to consideration is unconditional, excluding amount withheld under retainage provision in contract, to be collected in fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 910
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 6
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482546/910-10-50-6

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

Amount of right to consideration in exchange for good or service transferred to customer under long-term contract or program when right to consideration is unconditional, excluding amount withheld under retainage provision in contract, to be collected in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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

Amount of right to consideration in exchange for good or service transferred to customer under long-term contract or program when right to consideration is unconditional, excluding amount withheld under retainage provision in contract, to be collected in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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

Amount of right to consideration in exchange for good or service transferred to customer under long-term contract or program when right to consideration is unconditional, excluding amount withheld under retainage provision in contract, to be collected in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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

Amount of right to consideration in exchange for good or service transferred to customer under long-term contract or program when right to consideration is unconditional, excluding amount withheld under retainage provision in contract, to be collected in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).