Commitments and Contingencies - Legal Proceedings (Details) $ in Millions		9 Months Ended	12 Months Ended
	Jul. 16, 2018 USD ($) item	Sep. 30, 2018	Dec. 31, 2017	Dec. 07, 2011 director
Series B 9.375% redeemable preferred stock
Commitments and Contingencies
Preferred stock, dividend rate (as a percent)		9.375%	9.375%
Series C 9.125% redeemable preferred stock
Commitments and Contingencies
Preferred stock, dividend rate (as a percent)		9.125%	9.125%
Curtis J. Timm
Commitments and Contingencies
Number of directors elected by Preferred holders | director				2
Number of days within which special election for election of directors to be held	60 days
Number of quarterly payments of dividends sought for Preferred holders | item	3
Dividend amount required to be paid by company in three quartely payment | $	$ 1.2
Preferred B stock approval percentage	67.00%