(Loss) Earnings per Share (Details) - Calculations Of Basic And Diluted (Loss) Earnings Per Share - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Numerator:
Net (loss) income used for calculating basic and diluted (loss) earnings per common share	$ (92,281)	$ 51,626	$ (55,848)	$ 96,614
Denominator:
Weighted average number of common shares used in the calculation of basic (loss) earnings per share (in shares)	89,297	82,559	86,066	82,505
Common stock equivalents associated with stock-based compensation plans (in shares)	0	1,152	0	1,203
Shares used in the calculation of diluted (loss) earnings per share (in shares)	89,297	83,711	86,066	83,708
Basic (loss) earnings per share (in dollars per share)	$ (1.03)	$ 0.63	$ (0.65)	$ 1.17
Diluted (loss) earnings per share (in dollars per share)	$ (1.03)	$ 0.62	$ (0.65)	$ 1.15