Debt (Details) (USD $)	6 Months Ended										2 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Carrying Amount	Dec. 31, 2012 Carrying Amount	Jun. 30, 2013 Fair Value	Dec. 31, 2012 Fair Value	Jun. 30, 2013 Pfizer convertible subordinated note due 2014 Carrying Amount	Dec. 31, 2012 Pfizer convertible subordinated note due 2014 Carrying Amount	Jun. 30, 2013 Pfizer convertible subordinated note due 2014 Fair Value	Dec. 31, 2012 Pfizer convertible subordinated note due 2014 Fair Value	Jun. 30, 2013 4.75% convertible senior notes due 2015	Dec. 31, 2012 4.75% convertible senior notes due 2015	Jun. 30, 2013 4.75% convertible senior notes due 2015 Carrying Amount	Dec. 31, 2012 4.75% convertible senior notes due 2015 Carrying Amount	Jun. 30, 2013 4.75% convertible senior notes due 2015 Fair Value	Dec. 31, 2012 4.75% convertible senior notes due 2015 Fair Value
Convertible Notes
Interest rate of debt (as a percent)											4.75%	4.75%
Convertible subordinated notes	$ 9,287,000	$ 9,033,000					$ 9,287,000	$ 9,033,000	$ 17,379,000	$ 13,573,000
Convertible senior notes	214,530,000	322,043,000											214,530,000	322,043,000	643,152,000	798,040,000
Long-term debt, noncurrent			223,817,000	331,076,000	660,531,000	811,613,000
Aggregate principal amount of notes that can be converted into common stock											143,701,000
Common stock issued in conversion of notes (in shares)											16,376,175
Cash used to fund redemption of notes	$ 9,771,000										$ 9,800,000