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, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Numerator:
Net (loss) income used for calculating basic and diluted (loss) income per common share	$ (48,180)	$ 30,484	$ (104,028)	$ 127,097
Denominator:
Weighted average number of common shares used in the calculation of basic (loss) income per share (in shares)	90,624	82,638	87,585	82,549
Common stock equivalents associated with stock-based compensation plans (in shares)	0	1,165	0	1,212
Shares used in the calculation of diluted (loss) income per share (in shares)	90,624	83,803	87,585	83,761
Basic (loss) income per share (in dollars per share)	$ (0.53)	$ 0.37	$ (1.19)	$ 1.54
Diluted (loss) income per share (in dollars per share)	$ (0.53)	$ 0.36	$ (1.19)	$ 1.52