Fair Value Measurements (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 1991	Apr. 18, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Redemption amount of senior redeemable preferred stock			$ 2.1
Preferred stock dividend rate per annum	12.00%
Senior Redeemable Preferred Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amount of senior redeemable preferred stock				$ 2.1
Public Preferred Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Preferred stock dividend rate per annum	12.00%	6.00%
Public preferred stock par value (in dollar per share)	$ 0.01
Carrying value of public preferred stock	$ 131.6			127.7
Estimate of Fair Value, Fair Value Disclosure [Member] | Public Preferred Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Public preferred stock	$ 42.2			$ 31.9