Net Loss Per Common Share - Additional Information (Details) - shares shares in Millions	3 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2017	Aug. 31, 2017	Feb. 28, 2013
3.50% Convertible Notes
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Interest rate (as a percent)	3.50%
3.75% Convertible Senior Notes due 2022
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Interest rate (as a percent)	3.75%	3.75%		3.75%
Common stock not included in the calculation of potentially diluted shares	14.9
3.50% Convertible Notes
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Interest rate (as a percent)			3.50%		3.50%
Date of convertible debt retired	2018-02