Restructuring charges - Additional Information (Detail) (USD $)	12 Months Ended		3 Months Ended
	Dec. 31, 2010 Severance [Member]	Dec. 31, 2010 2010 plan [Member]	Jun. 30, 2010 2008 plan [Member]	Dec. 31, 2010 Spine [Member] 2010 plan [Member] Severance [Member]	Dec. 31, 2010 Orthopedics [Member] 2010 plan [Member] Severance [Member]
Restructuring Cost and Reserve [Line Items]
Recognition of restructuring expense	$ 3,550,000		$ 3,600,000	$ 400,000	$ 3,200,000
Restructuring Charges recorded in selling and marketing expenses		1,600,000
Restructuring Charges recorded in general and administrative expenses		$ 2,000,000