Rental Income (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Consolidated properties
Approximate future minimum rents to be received over the next five years and thereafter for non-cancelable operating leases
2012	$ 955,920
2013	919,388
2014	843,069
2015	755,334
2016	673,792
Thereafter	3,159,160
Total minimum lease payments	7,306,663
Unconsolidated properties
Approximate future minimum rents to be received over the next five years and thereafter for non-cancelable operating leases
2012	199,659
2013	196,868
2014	189,078
2015	184,372
2016	179,526
Thereafter	829,419
Total minimum lease payments	$ 1,778,922