Debt (Details) (USD $)	9 Months Ended								5 Months Ended						1 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Carrying Amount	Dec. 31, 2012 Carrying Amount	Sep. 30, 2013 Fair Value	Dec. 31, 2012 Fair Value	Dec. 31, 2012 Pfizer convertible subordinated note due 2014 Carrying Amount	Dec. 31, 2012 Pfizer convertible subordinated note due 2014 Fair Value	Sep. 30, 2013 4.75% convertible senior notes due 2015	Dec. 31, 2012 4.75% convertible senior notes due 2015	Sep. 30, 2013 4.75% convertible senior notes due 2015 Carrying Amount	Dec. 31, 2012 4.75% convertible senior notes due 2015 Carrying Amount	Sep. 30, 2013 4.75% convertible senior notes due 2015 Fair Value	Dec. 31, 2012 4.75% convertible senior notes due 2015 Fair Value	Aug. 31, 2013 Pfizer convertible subordinated note due 2013
Convertible Notes
Interest rate of debt (as a percent)									4.75%	4.75%
Convertible subordinated notes		$ 9,033,000					$ 9,033,000	$ 13,573,000
Convertible senior notes	187,136,000	322,043,000									187,136,000	322,043,000	955,974,000	798,040,000
Long-term debt, noncurrent			187,136,000	331,076,000	955,974,000	811,613,000
Aggregate principal amount of notes that can be converted into common stock									180,988,000						10,000,000
Common stock issued in conversion of notes (in shares)									20,625,403						1,025,641
Cash used to fund redemption of notes	$ 11,262,000								$ 11,300,000