Stockholders' Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions		2 Months Ended	3 Months Ended		9 Months Ended
	Aug. 02, 2018	Sep. 30, 2018	Sep. 30, 2018	Mar. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Common stock, shares authorized (in shares)		450,000,000	450,000,000		450,000,000	450,000,000
Common stock, par value (in dollars per share)		$ 0.01	$ 0.01		$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)		50,000,000	50,000,000		50,000,000	50,000,000
Preferred stock, par value (in dollars per share)		$ 0.01	$ 0.01		$ 0.01	$ 0.01
Common stock, shares issued (in shares)		133,765,392	133,765,392		133,765,392	107,121,235
Common shares outstanding (in shares)		133,765,392	133,765,392		133,765,392	107,121,235
Proceeds from issuance of common stock, net of offering costs				$ 275.9
Series B Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		6,770,393	6,770,393		6,770,393	6,770,393
Preferred stock, shares outstanding (in shares)		6,770,393	6,770,393		6,770,393	6,770,393
Preferred stock dividend percentage					8.00%
Series C Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares issued (in shares)		6,900,000	6,900,000		6,900,000	6,900,000
Preferred stock, shares outstanding (in shares)		6,900,000	6,900,000		6,900,000	6,900,000
Preferred stock dividend percentage					8.00%
Common Stock [Member]
Class of Stock [Line Items]
Issuance of stock (in shares)					15,525,000
Exchange of convertible senior notes for common stock (in shares)					10,744,577
Common Stock [Member] | Follow-on public offering [Member]
Class of Stock [Line Items]
Issuance of stock (in shares)				15,525,000
Price per share of issued stock (in dollars per share)				$ 17.77
2019 Notes [Member] | Convertible Debt [Member] | Common Stock [Member]
Class of Stock [Line Items]
Exchange of convertible senior notes for common stock (in shares)	10,020,328	724,250	10,744,577