Segment Reporting - Income From Investment Management (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Operating Expenses
Reimbursable costs from affiliates	$ 1,276	$ 4,786	$ 7,717	$ 12,475
Merger and other expenses	(596)	70	665	912
General and administrative	19,399	17,210	57,616	58,224
Subadvisor fees	0	1,763	1,469	5,615
Stock-based compensation expense	4,564	4,747	10,143	13,848
Depreciation and amortization	108,351	109,517	332,022	335,528
Total operating expenses	162,239	198,409	513,605	555,301
Other Income and Expenses
Equity in earnings of equity method investments in real estate	1,720	5,769	(10,087)	15,211
Other gains and (losses)	45,113	(12,402)	49,537	(12,118)
Total other income and expenses	15,229	(73,604)	(85,125)	(184,339)
Income before income taxes	155,409	45,992	303,218	181,899
(Provision for) benefit from income taxes	(5,975)	(4,157)	28,122	(5,147)
Net income	149,434	41,835	331,340	176,752
Net income attributable to noncontrolling interests	(37)	(496)	(10,553)	(881)
Net income attributable to W. P. Carey	149,397	41,339	320,787	175,871
Investment Management
Revenues
Gross contract revenue	5,024	15,251	26,320	45,038
Operating Expenses
Reimbursable costs from affiliates	1,276	4,786	7,717	12,475
Merger and other expenses	420	0	878	0
General and administrative	0	3,237	5,823	14,062
Subadvisor fees	0	1,763	1,469	5,615
Stock-based compensation expense	0	1,312	691	4,131
Depreciation and amortization	0	944	987	2,876
Total operating expenses	1,696	12,042	17,565	39,159
Other Income and Expenses
Equity in earnings of equity method investments in real estate	1,089	5,191	(12,494)	14,481
Other gains and (losses)	336	536	594	1,212
Total other income and expenses	1,425	5,727	(11,900)	15,693
Income before income taxes	4,753	8,936	(3,145)	21,572
(Provision for) benefit from income taxes	(2,339)	(646)	4,075	7,542
Net income	2,414	8,290	930	29,114
Net income attributable to noncontrolling interests	0	(507)	(9,865)	(975)
Net income attributable to W. P. Carey	2,414	7,783	(8,935)	28,139
Investment Management | Asset management revenue
Revenues
Gross contract revenue	3,748	9,878	18,109	29,400
Investment Management | Reimbursable costs from affiliates
Revenues
Gross contract revenue	1,276	4,786	7,717	12,475
Investment Management | Structuring and other advisory revenue
Revenues
Gross contract revenue	$ 0	$ 587	$ 494	$ 3,163