SEC Schedule III Rollforward of Real Estate Assets and Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation Of Carrying Amount Of Real Estate Investments Roll Forward
Real estate, Balance at beginning period	$ 16,822,358	$ 15,392,968	$ 15,287,078
Gross real estate balance at year end	18,391,542	16,966,657	16,433,600
Less: Assets sold and written-off	301,405	144,299	1,040,632
Real estate, Balance at end of period	18,090,137	16,822,358	15,392,968
Reconciliation Of Real Estate Accumulated Depreciation Roll Forward
Accumulated Depreciation, Balance at beginning of period	3,161,633	2,829,862	2,524,718
Additions charged to operating expenses	459,612	461,689	423,844
Real Estate Accumulated Depreciation	3,621,245	3,291,551	2,948,562
Less: Accumulated depreciation on assets sold and written-off	202,978	129,918	118,700
Accumulated Depreciation, Balance at end of period	3,418,267	3,161,633	2,829,862
Land [Member]
Reconciliation Of Carrying Amount Of Real Estate Investments Roll Forward
Additions during the period: Land	281,048	225,536	131,646
Building Improvements [Member]
Reconciliation Of Carrying Amount Of Real Estate Investments Roll Forward
Additions during the period: Buildings & improvements	$ 1,288,136	$ 1,348,153	$ 1,014,876