Segment Reporting - Income Statement (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information, Profit (Loss)
Revenues	$ 50,973	$ 45,715	$ 99,453	$ 89,513
Operating expenses	(39,130)	(40,030)	(76,105)	(77,513)
Interest expense	(11,791)	(10,320)	(23,244)	(20,680)
Other income and expenses, excluding interest expense	9,205	(2,952)	11,768	1,033
(Provision for) benefit from income taxes	(1,123)	133	(1,193)	(200)
Loss on sale of real estate, net of tax	0	0	0	(63)
Net income attributable to noncontrolling interests	(2,350)	(2,758)	(4,274)	(4,499)
Net Income (Loss) Attributable to CPA®:18 – Global	5,784	(10,212)	6,405	(12,409)
Operating Segments | Net Lease
Segment Reporting Information, Profit (Loss)
Revenues	28,882	27,169	56,252	54,631
Operating expenses	(18,319)	(15,438)	(34,355)	(30,722)
Interest expense	(6,999)	(7,263)	(13,994)	(14,580)
Other income and expenses, excluding interest expense	540	640	745	711
(Provision for) benefit from income taxes	(705)	405	(639)	226
Loss on sale of real estate, net of tax	0	0	0	(63)
Net income attributable to noncontrolling interests	(198)	(376)	(436)	(835)
Net Income (Loss) Attributable to CPA®:18 – Global	3,201	5,137	7,573	9,368
Operating Segments | Self Storage
Segment Reporting Information, Profit (Loss)
Revenues	13,856	12,397	27,049	22,706
Operating expenses	(11,663)	(16,500)	(23,752)	(30,248)
Interest expense	(3,039)	(2,734)	(6,044)	(4,995)
Other income and expenses, excluding interest expense	(308)	(9)	(406)	(17)
(Provision for) benefit from income taxes	(48)	(56)	(125)	(91)
Net Income (Loss) Attributable to CPA®:18 – Global	(1,202)	(6,902)	(3,278)	(12,645)
Operating Segments | Multi-family
Segment Reporting Information, Profit (Loss)
Revenues	6,452	5,439	12,620	10,756
Operating expenses	(4,554)	(4,131)	(8,880)	(8,048)
Interest expense	(1,434)	(1,211)	(2,586)	(2,419)
Other income and expenses, excluding interest expense	3	0	4	0
(Provision for) benefit from income taxes	(200)	(51)	(227)	(79)
Net income attributable to noncontrolling interests	34	(2)	23	(7)
Net Income (Loss) Attributable to CPA®:18 – Global	301	44	954	203
Operating Segments | All Other
Segment Reporting Information, Profit (Loss)
Revenues	1,783	710	3,532	1,420
Operating expenses	(2)	0	(10)	0
Net Income (Loss) Attributable to CPA®:18 – Global	1,781	710	3,522	1,420
Corporate
Segment Reporting Information, Profit (Loss)
Unallocated Corporate Overhead	3,889	(6,821)	1,495	(7,098)
Net income attributable to noncontrolling interests	$ (2,186)	$ (2,380)	$ (3,861)	$ (3,657)