Net Income (Loss) Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Basic EPS
Net income (loss)	$ (16,652)	$ 69,557	$ (8,944)	$ 63,660
Weighted average shares
Basic (in shares)	179,278,000	161,039,000	179,141,000	155,108,000
Effect of stock-based compensation plans (in shares)	0	4,789,000	0	3,284,000
Diluted (in shares)	179,278,000	165,828,000	179,141,000	158,392,000
Income (loss) per share
Basic (in dollars per share)	$ (0.09)	$ 0.43	$ (0.05)	$ 0.41
Diluted (in dollars per share)	$ (0.09)	$ 0.42	$ (0.05)	$ 0.40
Convertible Senior Notes Due March 2028 [Member]
Earnings Per Share (Textual) [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	3.25%		3.25%
Stock Options [Member]
Earnings Per Share (Textual) [Abstract]
Number of shares of common stock equivalents related to convertible debt	633,391	215,298	851,254	404,543