SEC Schedule III Rollforward of Real Estate Assets and Accumulated Depreciation (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reconciliation Of Carrying Amount Of Real Estate Investments Roll Forward
Real estate, Balance at beginning period	$ 18,238,218	$ 16,421,701	$ 16,193,864
Real Estate Accumulated Depreciation Period Increase Decrease	19,384,740	18,551,728	16,543,107
Less: Assets sold and written-off	1,030,114	313,510	121,406
Real estate, Balance at end of period	18,354,626	18,238,218	16,421,701
Reconciliation Of Real Estate Accumulated Depreciation Roll Forward
Accumulated Depreciation, Balance at beginning of period	3,072,269	2,874,529	2,520,818
Additions charged to operating expenses	423,844	427,189	452,793
Real Estate Accumulated Depreciation	3,496,113	3,301,718	2,973,611
Less: Accumulated depreciation on assets sold and written-off	85,180	229,449	99,082
Accumulated Depreciation, Balance at end of period	3,410,933	3,072,269	2,874,529
Land [Member]
Reconciliation Of Carrying Amount Of Real Estate Investments Roll Forward
Additions during the period: Land	131,646	514,950	33,481
Building Improvements [Member]
Reconciliation Of Carrying Amount Of Real Estate Investments Roll Forward
Additions during the period: Buildings & improvements	$ 1,014,876	$ 1,615,077	$ 315,762