Series A Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Mar. 17, 2017	Dec. 04, 2015
Class of Stock [Line Items]
Series A convertible preferred stock, issued (in shares)	800,000		800,000
Deemed dividend on preferred stock redemption	$ 0.0	$ (58.0)
Deemed dividend on modification of Series A Convertible Preferred Stock	0.0	(4.0)
Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Series A convertible preferred stock, issued (in shares)					820,000
Aggregate purchase price of preferred shares					$ 820.0
Preferred Stock, par value (in dollars per share)					$ 1,000
Direct Issuance Expenses					$ 26.0
Dividend rate					5.50%
Payments of Ordinary Dividends, Preferred Stock and Preference Stock	11.0	$ 12.0
Accrued Dividends	$ 3.0		$ 3.0
Conversion Price Per Share At Option Of Holder	$ 30
Conversion rate per preferred share	33.333
Secondary offering by the preferred shareholders				342,000
Redeemed Shares of Preferred stock				90,000
Preferred Stock, Redemption Price Per Share				$ 48.47
Financial instruments subject to redemption, settlement terms, maximum number of shares	27,900,000.0		27,500,000.0