Net income (loss) per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	27,011,919	16,766,410	27,011,919	42,234,469
Basic Net Income (Loss) Per Share
Net income (loss)	$ (39,582)	$ 59,293	$ (48,645)	$ (11,538)
Weighted average common shares outstanding	181,387,000	168,592,000	177,378,000	167,288,000
Basic net income (loss) per share	$ (0.22)	$ 0.35	$ (0.27)	$ (0.07)
Diluted Net Income (Loss) Per Share
Diluted net income (loss)	$ (39,582)	$ 62,167	$ (48,645)	$ (11,538)
Weighted average common shares outstanding	181,387,000	168,592,000	177,378,000	167,288,000
Dilutive stock options and RSU’s		10,038,000
Dilutive 2015 Notes		10,416,000
Weighted average shares used to compute diluted net income (loss) per share	181,387,000	189,046,000	177,378,000	167,288,000
Diluted net income (loss) per share	$ (0.22)	$ 0.33	$ (0.27)	$ (0.07)
Stock options and awards
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	12,520,799	2,275,884	12,520,799	17,328,082
Convertible Senior Notes 4.75 Percent Due 2015
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	632		632	10,415,861
Convertible Senior Notes 0.375 Percent Due 2018
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	7,245,263	7,245,263	7,245,263	7,245,263
Convertible Senior Notes 1.25 Percent Due 2020
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	7,245,225	7,245,263	7,245,225	7,245,263