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Basis of Presentation and Significant Accounting Policies (Deferred Finance Costs and Debt) (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Aug. 31, 2012	Mar. 31, 2012	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Jun. 30, 2015
Debt Instrument [Line Items]
Amortization of Financing Costs			$ 12.3	$ 12.2
Debt premium						$ 6.2
Secured Debt [Member]
Debt Instrument [Line Items]
Debt premium			6.2
Unamortized discount (premium), Net				(10.3)
Unsecured Debt [Member]
Debt Instrument [Line Items]
Unamortized discount (premium), Net			$ (7.4)	$ 5.9
Series G Cumulative Redeemable Preferred Stock
Debt Instrument [Line Items]
Preferred Units, Issued					4,000,000
Preferred stock dividend rate (percentage)		6.875%	6.875%		6.875%
Series H Cumulative Redeemable Preferred Stock
Debt Instrument [Line Items]
Preferred Units, Issued					4,000,000
Preferred stock dividend rate (percentage)	6.375%		6.375%		6.375%
Series G Cumulative Redeemable Preferred Unit [Member] \| Series G Cumulative Redeemable Preferred Stock
Debt Instrument [Line Items]
Preferred Units, Issued			4,000,000
Series H Cumulative Redeemable Preferred Unit [Member] \| Series H Cumulative Redeemable Preferred Stock
Debt Instrument [Line Items]
Preferred Units, Issued						4,000,000
Minimum [Member] \| Lease Agreements [Member]
Debt Instrument [Line Items]
Finite-Lived Intangible Asset, Useful Life			1 year
Maximum [Member] \| Lease Agreements [Member]
Debt Instrument [Line Items]
Finite-Lived Intangible Asset, Useful Life			20 years