Computation of Net (Loss) Income per Share - Calculations Of Basic And Diluted (Loss) Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net income (loss) used for calculating basic and diluted income (loss) per common share	$ 11,753	$ (48,180)	$ 38,436	$ (104,028)
Denominator:
Weighted average number of common shares used in the calculation of basic (loss) income per share (in shares)	90,854	90,624	90,969	87,585
Common stock equivalents associated with stock-based compensation plans (in shares)	1,294	0	1,275	0
Shares used in the calculation of diluted (loss) income per share (in shares)	92,148	90,624	92,244	87,585
Basic (loss) income per share (in dollars per share)	$ 0.13	$ (0.53)	$ 0.42	$ (1.19)
Diluted (loss) income per share (in dollars per share)	$ 0.13	$ (0.53)	$ 0.42	$ (1.19)