Net income (loss) per share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	19,618,454	42,616,520	32,736,493	42,616,520
Basic Net Income (Loss) Per Share
Net income (loss)	$ 9,294	$ (36,873)	$ (9,063)	$ (70,830)
Weighted average common shares outstanding	178,676,000	167,914,000	175,373,000	166,636,000
Basic net income (loss) per share	$ 0.05	$ (0.22)	$ (0.05)	$ (0.43)
Diluted Net Income (Loss) Per Share
Diluted net income (loss)	$ 9,294	$ (36,873)	$ (9,063)	$ (70,830)
Weighted average common shares outstanding	178,676,000	167,914,000	175,373,000	166,636,000
Dilutive stock options and RSU's	7,817,000
Weighted average shares used to compute diluted net income (loss) per share	186,493,000	167,914,000	175,373,000	166,636,000
Diluted net income (loss) per share	$ 0.05	$ (0.22)	$ (0.05)	$ (0.43)
Stock options and awards
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	137,012	17,684,266	13,255,051	17,684,266
Convertible Senior Notes 4.75 Percent Due 2015
Anti-dilutive securities
Potential common shares excluded from diluted net loss per share computation	4,990,916	10,441,728	4,990,916	10,441,728
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	7,245,263	7,245,263	7,245,263	7,245,263