Net Investments in Properties (Details 6) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Real Estate Under Construction [Abstract]
Beginning balance	$ 0us-gaap_ConstructionInProgressGross	$ 0us-gaap_ConstructionInProgressGross
Capitalized funds	20,617	0
Placed into service	(18,502)	0
Capitalized interest	143us-gaap_InterestCostsCapitalized	0us-gaap_InterestCostsCapitalized
Ending balance	$ 2,258us-gaap_ConstructionInProgressGross	$ 0us-gaap_ConstructionInProgressGross

Amount of assets under construction that are now placed into service as the balance sheet date.

No definition available.

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Namespace Prefix:	cpa18_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Construction costs capitalized to date on capital projects that have not been completed and assets being constructed that are not ready to be placed into service.

+ References

No definition available.

+ Details

Name:	cpa18_FundsCapitalizedForConstructionInProgress
Namespace Prefix:	cpa18_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	cpa18_RealEstateUnderConstructionAbstract
Namespace Prefix:	cpa18_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of structure or a modification to a structure under construction. Includes recently completed structures or modifications to structures that have not been placed into service.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6391035&loc=d3e2868-110229

+ Details

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

- Definition

Amount of interest capitalized during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Allowance for Funds Used during Construction

-URI http://asc.fasb.org/extlink&oid=6504829

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration