Fair Value Measurements (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Financial assets:
Investment in marketable securities, net	$ 9,347	$ 30,385
Financial liabilities:
Mortgages and notes payable	2,396,899	2,926,218
Credit facility	535,000	555,000
Other financings	0	8,477
Co-venture obligation	0	52,431
Carrying value
Financial assets:
Investment in marketable securities, net	9,347	30,385
Financial liabilities:
Mortgages and notes payable	2,396,899	2,926,218
Credit facility	535,000	555,000
Other financings	0	8,477
Co-venture obligation	0	52,431
Derivative liability	3,482	2,891
Fair value
Financial assets:
Investment in marketable securities, net	9,347	30,385
Financial liabilities:
Mortgages and notes payable	2,628,980	3,109,577
Credit facility	535,000	555,000
Other financings	0	8,477
Co-venture obligation	0	55,000
Derivative liability	$ 3,482	$ 2,891