8.00% Series A Convertible Preferred Stock - Narrative (Details) - USD ($)			1 Months Ended		6 Months Ended	12 Months Ended
	Jan. 23, 2018	Feb. 16, 2016	Apr. 30, 2018	Apr. 30, 2017	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Mar. 31, 2017
Temporary Equity [Line Items]
Class of warrant or right, number of securities called by warrants or rights (in shares) (up to)	1,500,000
Common stock, par value (in dollars per share)					$ 0.01	$ 0.01
Investment warrants, exercise price (in dollars per share)		$ 3.50
Direct and incremental fees	$ 700,000
Accrued dividends payable to Preferred Stockholders					$ 4,700,000		$ 4,400,000	$ 4,400,000
Dividends paid in additional shares of Preferred Stock			$ 4,700,000	$ 4,400,000
Dividends, Preferred Stock, Cash			$ 440	$ 0
Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Preferred stock, shares issued (in shares)					236,672	227,483
Beneficial conversion feature		$ 48,300,000
Preferred stock, dividend rate					8.00%	8.00%
Liquidation preference per share (in dollars per share)					$ 1,000
Dividends, paid-in-kind, period					7 years
Accrued dividends payable to Preferred Stockholders					$ 4,700,000
TCP-ASC ACHI Series LLLP | Redeemable Convertible Preferred Stock
Temporary Equity [Line Items]
Preferred stock, shares issued (in shares)		200,000
Preferred stock, issued, value		$ 200,000,000
Long-term purchase commitment, period		10 years
Direct and incremental fees		$ 21,300,000
Closing fees paid to investor		$ 14,000,000
Preferred stock, dividend rate		8.00%			8.00%
TCP-ASC ACHI Series LLLP | Common Stock
Temporary Equity [Line Items]
Long-term purchase commitment, period		10 years
Class of warrant or right, number of securities called by warrants or rights (in shares) (up to)		60,000,000
Investment warrants, exercise price (in dollars per share)		$ 3.50