Net income (loss) per share (Details 2) - shares	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
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