CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED)(Parentheticals) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Distributions of available cash	$ 2,029	$ 2,105	$ 3,945	$ 3,953

Amount of cash generated from operations, excluding capital proceeds, as reduced by operating expenses and debt service, excluding prepayments and lump-sum or "balloon" payments, that is available to distribute to the advisor.

No definition available.

Name:	cpa18_DistributionsOfAvailableCash
Namespace Prefix:	cpa18_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration