Leasing Activities (Schedule of Lease Receivables) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Lease Receivables [Line Items]
Operating Leases, Future Minimum Payments Receivable, Current	$ 870,201,000
Operating Leases, Future Minimum Payments Receivable, in Two Years	824,164,000
Operating Leases, Future Minimum Payments Receivable, in Three Years	752,470,000
Operating Leases, Future Minimum Payments Receivable, in Four Years	657,020,000
Operating Leases, Future Minimum Payments Receivable, in Five Years	559,194,000
Operating Leases, Future Minimum Payments Receivable, Thereafter	2,508,215,000
Operating Leases, Future Minimum Payments Receivable	6,171,264,000
Tenant Reimbursements	$ 201,800,000	$ 196,300,000	$ 174,200,000