Fair Value Measurement Disclosures - Estimated Fair Values of Financial Instruments (Parenthetical) (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
12.5% Senior Secured Notes due 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on senior secured notes	12.50%	12.50%
Significant other observable inputs (Level 2) | 12.5% Senior Secured Notes due 2017
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Interest rate on senior secured notes	12.50%	12.50%
Series B Preferred Stock
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cumulative exchangeable redeemable preferred stock dividend rate	10.75%	10.75%
Series B Preferred Stock | Significant unobservable inputs (Level 3)
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Cumulative exchangeable redeemable preferred stock dividend rate	10.75%	10.75%