Equity Investment in Real Estate and the Managed REITs (Narratives) (Details) (USD $)	3 Months Ended		9 Months Ended					1 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended						9 Months Ended		9 Months Ended	3 Months Ended		9 Months Ended				0 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014 Real Estate Investments	Sep. 30, 2013 Real Estate Investments	Dec. 31, 2013 Real Estate Investments	Jan. 31, 2014 CPA: 16 - Global	Sep. 30, 2013 CPA: 16 - Global	Jan. 31, 2014 CPA:16 - Global operating partnership	Sep. 30, 2013 CPA:16 - Global operating partnership	Sep. 30, 2014 CPA: 17 - Global	Sep. 30, 2013 CPA: 17 - Global	Sep. 30, 2014 CPA:17 - Global operating partnership	Sep. 30, 2013 CPA:17 - Global operating partnership	Sep. 30, 2014 CPA:18 - Global Class A	Sep. 30, 2014 CPA:18 - Global operating partnership	Sep. 30, 2014 CWI	Sep. 30, 2014 CWI operating partnership	Sep. 30, 2014 Managed REITs	Sep. 30, 2013 Managed REITs	Sep. 30, 2014 Managed REITs	Sep. 30, 2013 Managed REITs	Dec. 31, 2013 Managed REITs	Sep. 30, 2014 C1000 Logestiek Vastgoed B.V. Real Estate Investments	Jan. 31, 2014 Hellweg Die Profi-Baumarkte GmbH & Co. K.G CPA: 16 - Global Real Estate Investments	Jan. 31, 2014 The New York Times Company CPA: 16 - Global Real Estate Investments	Sep. 30, 2014 Beach House JV, LLC
Investments in REITs
Asset management fees receivable, shares												232,966				25,044		63,542
Aggregate unamortized basis difference on equity investments					$ 5,800,000		$ 16,600,000													$ 17,400,000		$ 17,400,000		$ 80,500,000
Other-than-temporary impairment charges										700,000	12,100,000									100,000	500,000	100,000	22,200,000
Gain or loss on sale of investment properties			24,188,000	290,000																800,000	2,400,000	13,300,000	(2,900,000)
Mortgage debt tenants in common																									86,800,000
Pro rata share mortgage debt on tenancy in common																									13,000,000
Other Transactions
Increase in ownership percentage of equity investments																										25.00%	27.00%
Distributions received from equity investment					9,000,000	10,400,000		6,400,000	18,900,000	4,800,000	11,200,000	3,300,000	2,100,000	15,400,000	12,700,000		1,200,000		2,200,000
Income from equity method investments	$ 11,610,000	$ 9,180,000	$ 35,324,000	$ 52,377,000																$ 100,000	$ 100,000	$ 100,000	$ 4,100,000					$ 700,000
Equity investment rate of return																												8.50%
Redeemable preferred units owned																												100
Common units owned																												0