Revisions of Previously-Issued Financial Statements (Narratives) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Used in Investing Activities	$ (53,326)	$ (144,773)
Net Cash Provided by Financing Activities	$ 51,347	247,265
Net cash provided by operating activities
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Adjustment to prior period financial statements		(1,000)
Effects of exchange rates on cash balance
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Adjustment to prior period financial statements		500
Interest expense
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Adjustment to prior period financial statements		(900)
Loss before income taxes
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Adjustment to prior period financial statements		(900)
Net loss
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Adjustment to prior period financial statements		(900)
Net loss attributable to CPA 18
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Adjustment to prior period financial statements		$ (900)
Net loss attributable to CPA 18 | Class A
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Impact on net loss per share from adjustments to prior period financial statements		$ (0.01)
Net loss attributable to CPA 18 | Class C
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Impact on net loss per share from adjustments to prior period financial statements		$ (0.01)
Other assets
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Adjustment to prior period financial statements		$ (900)
Total assets
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Adjustment to prior period financial statements		(900)
Distributions and accumulated losses
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Adjustment to prior period financial statements		(900)
Total equity
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Adjustment to prior period financial statements		(900)
Comprehensive loss
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Adjustment to prior period financial statements		(900)
Comprehensive loss attributable to CPA 18
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Adjustment to prior period financial statements		(900)
Revisions
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Used in Investing Activities		536
Net Cash Provided by Financing Activities		(975)
Revisions | Accruals
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by Financing Activities		(1,923)
Revisions | Capitalization and financing
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Net Cash Provided by Financing Activities		948
Revisions | Foreign currency re-measurement
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Adjustment to prior period financial statements		3,100
Additional Paid-In Capital
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Prior period adjustment		(3,200)
Common Stock
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Prior period adjustment		(3,200)
Treasury Stock
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Prior period adjustment		$ (3,200)