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
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net (loss) income used for calculating basic and diluted (loss) income per common share	$ (19,587)	$ 36,433
Denominator:
Weighted average number of common shares used in the calculation of basic (loss) income per share (in shares)	91,005	82,835
Common stock equivalents associated with stock-based compensation plans (in shares)	0	1,260
Shares used in the calculation of diluted (loss) income per share (in shares)	91,005	84,095
Basic (loss) income per share (in dollars per share)	$ (0.22)	$ 0.44
Diluted (loss) income per share (in dollars per share)	$ (0.22)	$ 0.43