Schedule III - Real Estate and Accumulated Depreciation (Reconciliation of Real Estate and Accumulated Depreciation) (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 the Beginning of the Year	$ 4,793,080	$ 4,834,111	$ 4,512,618
Additions:
Acquisitions	50,579	31,454	102,475
Capital Expenditures	90,619	133,550	336,281
Less:
Dispositions	(208,109)	(206,035)	(117,263)
Balance at the End of the Year	4,726,169	4,793,080	4,834,111
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance at the beginning of the year	865,710	776,078	716,957
Real Estate Accumulated Depreciation Additions [Abstract]
Depreciation expense — continuing operations	154,095	157,691	133,740
Depreciation expense — discontinued operations	2,143	1,185	1,554
Real Estate Accumulated Depreciation Less Dispositions [Abstract]
Dispositions	(67,283)	(69,244)	(76,173)
Balance at the end of the year	$ 954,665	$ 865,710	$ 776,078