Fair Value of Financial Instruments - Additional Information (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Mar. 15, 2018	Dec. 31, 2017
Convertible Notes | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of long-term debt	$ 248.9		$ 258.3
Secured Debt | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of long-term debt		$ 16.6
Embedded Derivative Financial Instruments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Change in fair value of embedded derivative liability	$ 0.6