Net income (loss) per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic Net Income (Loss) Per Share
Basic net income (loss)	$ 29,176	$ 36,054	$ 40,430	$ (163,513)
Weighted average common shares outstanding	212,627,000	206,796,000	212,172,000	202,399,000
Basic net income (loss) per share	$ 0.14	$ 0.17	$ 0.19	$ (0.81)
Diluted Net Income (Loss) Per Share
Diluted net income (loss)	$ 29,176	$ 36,054	$ 40,430	$ (163,513)
Weighted average common shares outstanding	212,627,000	206,796,000	212,172,000	202,399,000
Dilutive stock options and RSU’s	3,337,000	5,814,000	3,344,000
Weighted average shares used to compute diluted net income (loss) per share	215,964,000	212,610,000	215,516,000	202,399,000
Diluted net income (loss) per share	$ 0.14	$ 0.17	$ 0.19	$ (0.81)
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	9,572,684	2,917,934	7,772,454	13,173,184
Stock Options
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	9,055,004	2,399,468	7,254,774	12,654,718
Convertible Senior Notes 0.375 Percent Due 2018
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	148,741	149,527	148,741	149,527
Convertible Senior Notes 1.25 Percent Due 2020
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	368,939	368,939	368,939	368,939

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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