Rental Income (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012
Consolidated properties
Approximate future minimum rents to be received over the next five years and thereafter for non-cancelable operating leases
2013	$ 989,702
2014	917,638
2015	863,405
2016	801,448
2017	717,112
Thereafter	3,915,024
Total minimum lease payments	8,204,329
Unconsolidated properties
Approximate future minimum rents to be received over the next five years and thereafter for non-cancelable operating leases
2013	214,291
2014	208,617
2015	195,122
2016	185,113
2017	168,718
Thereafter	720,492
Total minimum lease payments	$ 1,692,353