Equity Investment in Real Estate and the Managed REITs (Narratives) (Details) (USD $)	3 Months Ended		6 Months Ended					1 Months Ended	6 Months Ended	1 Months Ended	6 Months Ended						6 Months Ended		6 Months Ended	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			0 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Real Estate Investments	Jun. 30, 2013 Real Estate Investments	Dec. 31, 2013 Real Estate Investments	Jan. 31, 2014 CPA: 16 - Global	Jun. 30, 2013 CPA: 16 - Global	Jan. 31, 2014 CPA:16 - Global operating partnership	Jun. 30, 2013 CPA:16 - Global operating partnership	Jun. 30, 2014 CPA: 17 - Global	Jun. 30, 2013 CPA: 17 - Global	Jun. 30, 2014 CPA:17 - Global operating partnership	Jun. 30, 2013 CPA:17 - Global operating partnership	Jun. 30, 2014 CPA:18 - Global Class A	Jun. 30, 2014 CPA:18 - Global operating partnership	Jun. 30, 2014 CWI	Jun. 30, 2014 CWI operating partnership	Jun. 30, 2014 Managed REITs	Jun. 30, 2013 Managed REITs	Jun. 30, 2014 Managed REITs	Jun. 30, 2013 Managed REITs	Dec. 31, 2013 Managed REITs	Jun. 30, 2014 Managed REITs	Jun. 30, 2013 Managed REITs	Jun. 30, 2014 Managed REITs	Jun. 30, 2013 Managed REITs	Jun. 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	Jun. 30, 2014 Beach House JV, LLC
Investments in REITs
Asset management fees receivable, shares												240,372				21,554		59,469
Aggregate unamortized basis difference on equity investments					$ 5,800,000		$ 16,600,000													$ 15,100,000		$ 15,100,000		$ 80,500,000
Other-than-temporary impairment charges										700,000	5,500,000										12,400,000		21,700,000		0	2,844,000	735,000	5,528,000
Gain or loss on sale of investment properties			23,930,000	50,000																(12,500,000)	(16,700,000)	(12,500,000)	(14,000,000)
Mortgage debt tenants in common																													93,800,000
Pro rata share mortgage debt on tenancy in common																													14,100,000
Other Transactions
Increase in ownership percentage of equity investments																														25.00%	27.00%
Distributions received from equity investment					5,500,000	6,900,000		6,400,000	12,500,000	4,800,000	7,400,000	2,100,000	1,300,000	9,300,000	9,100,000		600,000		1,100,000
Income from equity method investments	$ 9,452,000	$ 32,541,000	$ 23,714,000	$ 43,197,000																	$ 2,300,000		$ 4,000,000		$ 769,000	$ 2,717,000	$ 1,549,000	$ 3,544,000
Equity investment rate of return																																8.50%
Redeemable preferred units owned																																100
Common units owned																																0