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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Numerator:
Net income (loss) used for calculating basic and diluted income (loss) per common share	$ 46,270	$ (92,281)	$ 26,683	$ (55,848)
Denominator:
Weighted average number of common shares used in the calculation of basic (loss) income per share (in shares)	91,048	89,297	91,026	86,066
Common stock equivalents associated with stock-based compensation plans (in shares)	1,108	0	1,226	0
Shares used in the calculation of diluted (loss) income per share (in shares)	92,156	89,297	92,252	86,066
Basic (loss) income per share (in dollars per share)	$ 0.51	$ (1.03)	$ 0.29	$ (0.65)
Diluted (loss) income per share (in dollars per share)	$ 0.50	$ (1.03)	$ 0.29	$ (0.65)