Fair Value Measurement Disclosures - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Carrying Amount | Significant other observable inputs (Level 2) | 12.5% Senior Secured Notes
Estimated fair values of financial instruments
12.5% senior secured notes	$ 249.9	$ 260.3
Carrying Amount | Series B Preferred Stock | Significant unobservable inputs (Level 3)
Estimated fair values of financial instruments
10 3/4% Series B cumulative exchangeable redeemable preferred stock	175.3	165.6
Fair Value | Significant other observable inputs (Level 2) | 12.5% Senior Secured Notes
Estimated fair values of financial instruments
12.5% senior secured notes	258.6	269.1
Fair Value | Series B Preferred Stock | Significant unobservable inputs (Level 3)
Estimated fair values of financial instruments
10 3/4% Series B cumulative exchangeable redeemable preferred stock	$ 37.8	$ 38.1