Finance Receivables - Net Investments in Direct Financing Leases (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Receivables [Abstract]
Lease payments receivable	$ 53,555	$ 55,278
Unguaranteed residual value	39,401	39,401
Gross investments in direct financing leases	92,956	94,679
Less: unearned income	(50,796)	(52,625)
Less: allowance for credit losses	(11,768)	0
Net investment in direct financing leases	$ 30,392	$ 42,054

Direct Financing Lease, Net Investment in Lease, Excluding Deferred Selling Profit

No definition available.

Name:	cpa18_DirectFinancingLeaseNetInvestmentinLeaseExcludingDeferredSellingProfit
Namespace Prefix:	cpa18_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of deferred selling profit from direct financing lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 30
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=121576215&loc=SL77919379-209981

+ Details

Name:	us-gaap_DirectFinancingLeaseDeferredSellingProfit
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value of lease payments not yet received by lessor and amount expected to be derived from underlying asset, following end of lease term, guaranteed by lessee or other third party unrelated to lessor, from direct financing lease.

+ References

+ Details

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

- Definition

Amount of net investment in direct financing lease.

+ References

+ Details

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

- Definition

Amount of allowance for credit loss on net investment in direct financing lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (f)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=121599878&loc=SL82895884-210446

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919249-210447

+ Details

Name:	us-gaap_DirectFinancingLeaseNetInvestmentInLeaseAllowanceForCreditLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Present value expected to be derived from underlying asset, following end of lease term, not guaranteed by lessee or other third party unrelated to lessor.

+ References

+ Details

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

- References

No definition available.

+ Details

Name:	us-gaap_ReceivablesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration