Liability related to sale of future royalties - Additional Information (Detail) (USD $) In Millions, unless otherwise specified				3 Months Ended	6 Months Ended	9 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	9 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Mar. 31, 2012 CIMZIA and MIRCERA [Member]	Sep. 30, 2012 CIMZIA and MIRCERA [Member]	Sep. 30, 2012 CIMZIA and MIRCERA [Member]	Jun. 30, 2012 Milestone Scenario One [Member]	Dec. 31, 2012 Milestone Scenario One [Member]	Jun. 30, 2012 Milestone Scenario Two [Member]	Dec. 31, 2012 Milestone Scenario Two [Member]	Sep. 30, 2012 Purchase and Sale Agreement with RPI [Member]
Proceeds from sale of royalty rights											$ 124.0
Transaction costs related to sale of potential future royalties											4.4
Royalty revenues				2.7	6.9	9.6
Annual interest rate	17.00%	17.00%	17.00%
Potential payments milestone not achieved year one								3.0
Potential payments milestone not achieved year two										$ 7.0
Royalty agreement contingent payment description							If certain worldwide net sales thresholds of MIRCERAfor the 12 month period ending on December 31, 2012 are not achieved		If certain worldwide net sales thresholds of MIRCERAfor the 12 month period ending on December 31, 2013 are not achieved