Preferred Stock - Additional Information (Details) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) shares	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) Tranche $ / shares shares	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($) shares
Class Of Stock [Line Items]
Number of tranches sold to investors | Tranche			2
Preferred Series A dividends payable | $	$ 22.9		$ 22.9		$ 22.9
Preferred stock dividend paid | $	22.9		$ 68.8
Preferred stock dividend per share | $ / shares			$ 23.75
Accrued preferred dividends payable date			Nov. 14, 2018
Deemed dividends on Series A Preferred Stock | $	$ 7.4	$ 6.5	$ 21.5	$ 19.0
Series A Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Issued	965,100		965,100		965,100
Private Placement [Member] | Series A Warrants [Member]
Class Of Stock [Line Items]
Warrants exercisable	13,550,004		13,550,004
Private Placement [Member] | Series B Warrants [Member]
Class Of Stock [Line Items]
Warrants exercisable	6,533,727		6,533,727
Private Placement [Member] | Series A Preferred Stock [Member]
Class Of Stock [Line Items]
Preferred Stock, Shares Issued	965,100		965,100