Real Estate And Accumulated Depreciation (Total Cost Of The Properties) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance at beginning of year	$ 4,789,145	$ 4,262,959	$ 4,076,094
Additions at cost	137,462	654,513	319,789
Retirements or sales	(334,105)	(126,666)	(79,608)
Property held for sale	(78,721)	(1,563)	(53,163)
Impairment loss	(14,922)	(98)	(153)
Balance at end of year	$ 4,498,859	$ 4,789,145	$ 4,262,959