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, 2014		Dec. 31, 2013		Dec. 31, 2012
Reconciliation of Carrying Amount of Real Estate Investments [Roll Forward]
Balance at the Beginning of the Year	$ 4,669,289		$ 4,726,169		$ 4,793,080
Additions:
Acquisitions	0		347,510		50,579
Capital Expenditures	132,149		109,740		90,619
Less:
Dispositions	(126,471)		(474,275)		(168,408)
SEC Schedule III, Real Estate, Other Deductions	(43,839)		(39,855)		(39,701)
Balance at the End of the Year	4,631,128		4,669,289		4,726,169
Real Estate Held-for-sale	27,436	[1]	0	[1]	0
Operating properties	4,603,692		4,669,289		4,726,169
Reconciliation of Real Estate Accumulated Depreciation [Roll Forward]
Balance at the beginning of the year	983,808		954,665		865,710
Real Estate Accumulated Depreciation Additions [Abstract]
Depreciation expense — continuing operations	160,641		150,236		154,095
Depreciation expense — discontinued operations	0		9,164		2,143
Real Estate Accumulated Depreciation Less Dispositions [Abstract]
Dispositions	(22,459)		(91,890)		(28,270)
SEC Schedule III, Real Estate Accumulated Depreciation, Other Deductions	(42,994)		(38,367)		(39,013)
Balance at the end of the year	1,078,996		983,808		954,665
SchIIIRealEstateAccumulatedDepreciationAssetsHeldForSale	(11,167)		0		0
Real Estate Investment Property, Accumulated Depreciation	1,067,829		983,808
Accumulated Depreciation, including HFS [Member]
Real Estate Accumulated Depreciation Less Dispositions [Abstract]
Real Estate Investment Property, Accumulated Depreciation	$ 1,067,829		$ 983,808		$ 954,665

[1] (a)Real estate investments related to assets held for sale above represents gross real estate assets and does not include accumulated depreciation or other assets on the balance sheets of the properties held for sale.