Long-term Debt - Summary of Long-term Debt (Parenthetical) (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
6% Convertible Notes Due 2023
Debt Instrument [Line Items]
Debt stated interest rate percentage	6.00%	6.00%
Debt, maturity year	2023	2023
10% senior secured notes due 2019
Debt Instrument [Line Items]
Debt stated interest rate percentage	10.00%	10.00%
Debt, maturity year	2019	2019
10% second lien notes due 2019
Debt Instrument [Line Items]
Debt stated interest rate percentage	10.00%	10.00%
Debt, maturity year	2019	2019