Condensed Consolidated Statements of Income (Unaudited) (Parentheticals) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Distributions of available cash	$ 1,710	$ 2,196	$ 6,445	$ 6,057

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