Liability related to sale of future royalties - Summary of Liability Related to Potential Future Royalties (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Schedule Of Other Liabilities [Line Items]
Proceeds from sale of future royalties	$ 124,000
Non-cash interest expense	12,641
CIMZIA®and MIRCERA®royalties	(6,895)
Total liability related to sale of future royalties	129,746
Less: current portion	(3,000)
Liability related to sale of future royalties, non-current portion:	$ 126,746