Equity Investment in Real Estate and the Managed REITs (Details 5) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Investmens in REITs
Equity method investments	$ 564,092	$ 565,626
Real Estate Investments
Investmens in REITs
Equity method investments	211,065	212,481
Advanced Micro Devices | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	33.00%
Equity method investments	24,027	23,667
Builders FirstSource, Inc. | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	40.00%
Equity method investments	5,097	5,138
C1000 Logestiek Vastgoed B.V. | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	15.00%
Equity method investments	13,824	14,929
Del Monte Corporation | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	50.00%
Equity method investments	7,969	8,318
The Upper Deck Company | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	50.00%
Equity method investments	7,187	7,198
Waldaschaff Automotive GmbH and Wagon Automotive Nagold GmbH | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	33.00%
Equity method investments	6,173	6,323
The Talaria Company (Hinckley) | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	30.00%
Equity method investments	7,842	7,702
PETsMart, Inc. | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	30.00%
Equity method investments	3,825	3,808
SaarOTEC | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	50.00%
Equity method investments	(176)	(116)
SchulerA.G. | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	67.00%
Equity method investments	62,564	62,006
The New York Times Company | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	18.00%
Equity method investments	20,836	20,584
U.S. Airways Group, Inc. | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	75.00%
Equity method investments	7,928	7,995
Consolidated Systems, Inc. | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	60.00%
Equity method investments	3,249	3,278
Hellweg Die Profi-Baumarkte GmbH & Co. K.G | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	40.00%
Equity method investments	40,236	42,387
Wanbishi Archives Co. Ltd. | Real Estate Investments
Investmens in REITs
Equity method investment, ownership percentage	3.00%
Equity method investments	$ 484	$ (736)