Real Estate And Accumulated Depreciation (Total Cost Of The Properties) (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]
Balance at beginning of year	$ 4,262,959	$ 4,076,094	$ 4,289,276
Additions at cost	654,513	319,789	144,474
Retirements or sales	(126,666)	(79,608)	(348,221)
Property held for sale	(1,563)	(53,163)	(9,435)
Impairment loss	(98)	(153)	0
Impairment loss	$ 4,789,145	$ 4,262,959	$ 4,076,094