Equity Investment in Real Estate and the Managed REITs (Narratives) (Details) (USD $)	3 Months Ended		6 Months Ended		1 Months Ended	3 Months Ended		6 Months Ended												1 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jan. 31, 2013 Wanbishi Archives Co. Ltd.	Jun. 30, 2013 Managed REITs	Jun. 30, 2012 Managed REITs	Jun. 30, 2013 Managed REITs	Jun. 30, 2012 Managed REITs	Jun. 30, 2013 Managed REITs CPA: 16 - Global	Jun. 30, 2012 Managed REITs CPA: 16 - Global	Jun. 30, 2013 Managed REITs CPA:16 - Global operating partnership	Jun. 30, 2012 Managed REITs CPA:16 - Global operating partnership	Jun. 30, 2013 Managed REITs CPA: 17 - Global	Jun. 30, 2012 Managed REITs CPA: 17 - Global	Jun. 30, 2013 Managed REITs CPA:17 - Global operating partnership	Jun. 30, 2012 Managed REITs CPA:17 - Global operating partnership	Jun. 30, 2013 Managed REITs CWI	Jun. 30, 2013 Real Estate	Jun. 30, 2013 Real Estate U.S. Airways Group, Inc.
Investments in REITs
Asset management fees receivable, shares										170,547				176,621				23,129
Distributions received from equity investment			$ (22,338,000)	$ (17,013,000)						$ 12,500,000	$ 12,100,000	$ 7,400,000	$ 7,900,000	$ 1,300,000	$ 600,000	$ 9,100,000	$ 6,600,000
Gain or loss on sale of investment properties						(16,700,000)	34,300,000	(14,000,000)	31,900,000
Other-than-temporary impairment charges	2,844,000	3,234,000	5,528,000	3,532,000								5,500,000	3,500,000
Impairment charges	0	0	1,071,000	0		12,400,000	0	21,700,000	2,500,000
Income from equity method investments	32,541,000	28,345,000	43,197,000	42,331,000		2,300,000		4,000,000	100,000
Mortgage debt tenants in common																			167,600,000
Pro Rata Share Mortgage Debt On Tenancy In Common																			62,200,000
Purchase price adjustment					1,300,000
Disposition of Unconsolidated Real Estate Investment
Payments to acquire equity method investments			1,455,000	180,000																2,900,000
Proceeds from Issuance of Secured Debt			99,000,000	1,250,000																13,900,000
Repayments of Secured Debt			121,836,000	10,262,000																17,100,000
Proceeds from the sales of real estate investment																				28,400,000
Gain on sale of real estate investment																				$ 19,500,000