Fair Value Measurement Disclosures - Estimated Fair Values of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
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 8)	$ 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	172.9	165.6
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 8)	252.1	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	$ 39.7	$ 38.1