Consolidated Balance Sheets Parenthetical - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Allowance for receivables	$ 10.4	$ 9.9
Preferred Stock, Shares Authorized	2,357,299	2,357,299
Preferred Stock, 6 3/4% Cumulative Convertible, Shares Issued	155,250	155,250
Preferred Stock, 6 3/4% Cumulative Convertible, Shares Outstanding	155,250	155,250
Preferred Stock, Depositary Shares	3,105,000	3,105,000
Preferred Stock, Dividend Rate, Percentage	6.75%	6.75%
Preferred Stock, Liquidation Preference Per Share	$ 1,000	$ 1,000
Preferred Stock Liquidation Preference Per Depositary Share	50	50
Common Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Common Stock, Shares Authorized	96,000,000	96,000,000
Common Stock, Shares, Issued	42,197,965	42,056,237
Common Stock, Shares, Outstanding	42,197,965	42,056,237