Fair Value Measurements (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2016	Dec. 31, 1991	Dec. 31, 2015
Senior Redeemable Preferred Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying amount of senior redeemable preferred stock	$ 2.1		$ 2.0
Preferred stock dividend rate per annum	14.125%
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 (Reported) Amount, Fair Value Disclosure [Member] | Public Preferred Stock [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Public preferred stock	$ 126.8		123.9
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	$ 23.9		$ 32.3