Intangible Assets and Liabilities - Narratives (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Intangible Assets And Liabilities [Abstract]
Net amortization of intangibles	$ 4.4	$ 6.8	$ 14.3	$ 22.4

The aggregate expense charged against earnings to allocate the cost of intangible assets and liabilities (nonphysical assets not used in production) in a systematic and rational manner to the periods expected to benefit from such assets. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

No definition available.

Name:	cpa18_NetAmortizationOfIntangibles
Namespace Prefix:	cpa18_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration