Net income (loss) per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Basic Net Income (Loss) Per Share
Net income (loss)	$ 24,047	$ (18,359)
Weighted average common shares outstanding	187,184	172,070
Basic net income (loss) per share	$ 0.13	$ (0.11)
Diluted Net Income (Loss) Per Share
Diluted net income (loss)	$ 24,047	$ (18,359)
Weighted average common shares outstanding	187,184	172,070
Dilutive stock options and RSU’s	5,441,000
Weighted average shares used to compute diluted net income (loss) per share	192,625	172,070
Diluted net income (loss) per share	$ 0.12	$ (0.11)
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	17,138,793	39,470,319
Stock Options
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	2,652,265	14,626,717
4.75% Convertible Senior Notes due 2015
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation		10,353,076
Interest rate of debt (as a percent)		4.75%
0.375% Convertible Senior Notes due 2018
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	7,245,244	7,245,263
1.25% Convertible Senior Notes due 2020
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	7,241,284	7,245,263