Loss Per Common Share - Additional Information (Detail) - USD ($) $ in Thousands, shares in Millions		3 Months Ended		6 Months Ended
	May 02, 2017	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Loss Per Common Share [Line Items]
Convertible senior notes principal amount		$ 517,500		$ 517,500		$ 517,500
2.25% Convertible Senior Notes due 2024
Loss Per Common Share [Line Items]
Common share equivalents excluded from computation of earnings per share	6.8
Convertible senior notes principal amount	$ 517,500
Stock Options, Unvested RSUs and PRSUs
Loss Per Common Share [Line Items]
Common share equivalents excluded from computation of earnings per share		7.5	5.0	7.5	5.0