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Real Estate - Real Estate Assets (Detail) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2013
Dec. 31, 2012
Industrial operating properties:    
Improved land $ 4,063,059 $ 5,317,123
Buildings and improvements 13,458,016 17,291,125
Development portfolio, including cost of land 884,352 951,643
Land 1,754,053 1,794,364
Other real estate investments 436,328 454,868
Total investments in real estate properties 20,595,808 25,809,123
Less accumulated depreciation 2,292,946 2,480,660
Net investments in real estate properties $ 18,302,862 $ 23,328,463