Net loss per share (Details) (USD $)	9 Months Ended				5 Months Ended	9 Months Ended		1 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013 Stock options	Sep. 30, 2012 Stock options	Sep. 30, 2013 4.75% Senior Notes	Sep. 30, 2013 4.75% Senior Notes	Sep. 30, 2012 4.75% Senior Notes	Dec. 31, 2012 Pfizer Note due 2013	Sep. 30, 2012 Pfizer Note due 2013	Aug. 31, 2013 Pfizer Note due 2014	Sep. 30, 2012 Pfizer Note due 2014
Anti-dilutive securities
Interest rate of debt (as a percent)					4.75%	4.75%	4.75%
Potential common shares excluded from diluted net loss per share computation	46,024,293	70,236,979	21,065,995	22,165,802		24,958,298	45,584,040		1,461,496		1,025,641
Aggregate principal amount of notes to be converted					$ 181,000,000			$ 10,000,000		$ 10,000,000
Common stock issued in conversion of notes (in shares)					20,625,403			1,461,496		1,025,641