SEC Schedule III Rollforward of Real Estate Assets and Accumulated Depreciation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation Of Carrying Amount Of Real Estate Investments Roll Forward
Real estate, Balance at beginning period	$ 18,090,137	$ 16,822,358	$ 15,392,968
Gross real estate balance at year end	19,195,201	18,391,542	16,966,657
Less: Assets sold and written-off and deconsolidated	855,243	301,405	144,299
Real estate, Balance at end of period	18,339,958	18,090,137	16,822,358
Reconciliation Of Real Estate Accumulated Depreciation Roll Forward
Accumulated Depreciation, Balance at beginning of period	3,418,267	3,161,633	2,829,862
Additions charged to operating expenses	478,788	459,612	461,689
Real Estate Accumulated Depreciation	3,897,055	3,621,245	3,291,551
Less: Accumulated depreciation on assets sold and written-off and deconsolidated	383,481	202,978	129,918
Accumulated Depreciation, Balance at end of period	3,513,574	3,418,267	3,161,633
Land
Reconciliation Of Carrying Amount Of Real Estate Investments Roll Forward
Additions during the period: Land	30,805	281,048	225,536
Building Improvements
Reconciliation Of Carrying Amount Of Real Estate Investments Roll Forward
Additions during the period: Buildings & improvements	$ 1,074,259	$ 1,288,136	$ 1,348,153