Real Estate Investments And Accumulated Depreciation (Schedule Of Changes In Rental Properties And Accumulated Depreciation) (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Real Estate Investments And Accumulated Depreciation [Abstract]      
Rental Properties, Balance at beginning of year $ 4,804,867 $ 4,807,718 $ 4,958,179
Rental Properties, Additions 1,179,365 819,535 219,227
Rental Properties, Rental property held for sale (310,089) (79,200)
Rental Properties, Properties sold (538,424) (695,837) (82,015)
Rental Properties, Impairments (255,849)
Rental Properties, Retirements/disposals (32,875) (47,349) (31,824)
Rental Properties, Balance at end of year 5,102,844 [1] 4,804,867 4,807,718
Accumulated Depreciation, Balance at beginning of year 1,332,073 1,464,482 1,414,305
Accumulated Depreciation, Depreciation expense 154,343 151,569 147,447
Accumulated Depreciation, Rental property held for sale (126,503) (31,792)
Accumulated Depreciation, Properties sold (217,625) (204,837) (7,517)
Accumulated Depreciation, Repurposed buildings (22,330)
Accumulated Depreciation, Impairments (57,929)
Accumulated Depreciation, Retirements/disposals (32,875) (47,349) (31,824)
Accumulated Depreciation, Balance at end of year $ 1,087,083 [2] $ 1,332,073 $ 1,464,482
[1] Properties identified as held for sale at December 31, 2017 are excluded.
[2] Depreciation of buildings and improvements are calculated over lives ranging from the life of the lease to 40 years.