Real Estate And Accumulated Depreciation (Total Cost Of The Properties) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance at beginning of year	$ 4,688,526	$ 4,777,794	$ 4,658,396
Additions at cost	310,454	180,956	195,499
Retirements or sales	(608,466)	(123,252)	(70,924)
Property held for sale	0	(94,761)	0
Property transferred from held for sale (see Note 15)	18,090	0	0
Impairment loss	(8,754)	(52,211)	(5,177)
Balance at end of year	$ 4,399,850	$ 4,688,526	$ 4,777,794