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 Net Income (Loss) Per Share
Net income (loss)	$ 36,054	$ 36,877	$ (163,513)	$ 95,349
Weighted average common shares outstanding	206,796,000	188,029,000	202,399,000	187,632,000
Basic net income (loss) per share	$ 0.17	$ 0.20	$ (0.81)	$ 0.51
Diluted Net Income (Loss) Per Share
Diluted net income (loss)	$ 36,054	$ 36,877	$ (163,513)	$ 95,349
Weighted average common shares outstanding	206,796,000	188,029,000	202,399,000	187,632,000
Dilutive stock options and RSU’s	5,814,000	6,236,000		6,122,000
Weighted average shares used to compute diluted net income (loss) per share	212,610,000	194,265,000	202,399,000	193,754,000
Diluted net income (loss) per share	$ 0.17	$ 0.19	$ (0.81)	$ 0.49
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	2,917,934	17,605,587	13,173,184	17,433,642
Stock Options
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	2,399,468	3,119,097	12,654,718	2,947,152
0.375% Convertible Senior Notes due 2018
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	149,527	7,245,206	149,527	7,245,206
1.25% Convertible Senior Notes due 2020
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	368,939	7,241,284	368,939	7,241,284