Leasing Activity (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011
Operating Leases, Future Minimum Payments Receivable [Abstract]
Operating Leases, Future Minimum Payments Due, 2012	$ 471,541
Operating Leases, Future Minimum Payments Due, 2013	418,995
Operating Leases, Future Minimum Payments Due, 2014	352,486
Operating Leases, Future Minimum Payments Due, 2015	288,527
Operating Leases, Future Minimum Payments Due, 2016	230,557
Operating Leases, Future Minimum Payments, Due Thereafter	677,843
Operating Leases, Future Minimum Payments Due	$ 2,439,949