Fair Value Measurement Disclosures - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Carrying Amount | Significant other observable inputs (Level 2) | 12.5% Senior Secured Notes due 2017
Estimated fair values of financial instruments
12.5% Senior Secured Notes due 2017 (note 10)	$ 249.9	$ 249.9
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	177.7	175.3
Fair Value | Significant other observable inputs (Level 2) | 12.5% Senior Secured Notes due 2017
Estimated fair values of financial instruments
12.5% Senior Secured Notes due 2017 (note 10)	262.2	258.6
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	$ 45.4	$ 37.8