Summary of significant accounting policies - Additional Information (Detail) (USD $)	3 Months Ended								12 Months Ended						1 Months Ended	12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012 Unit	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012 Musculoskeletal Transplant Foundation ("MTF") [Member]	Dec. 31, 2012 Customers and distributors based in Europe [Member]	Dec. 31, 2012 Interest Expense [Member]	Jan. 31, 2012 Collaborative Arrangement [Member] Musculoskeletal Transplant Foundation ("MTF") [Member] Years	Dec. 31, 2012 Collaborative Arrangement [Member] Musculoskeletal Transplant Foundation ("MTF") [Member]	Dec. 31, 2011 Collaborative Arrangement [Member] Musculoskeletal Transplant Foundation ("MTF") [Member]	Dec. 31, 2010 Collaborative Arrangement [Member] Musculoskeletal Transplant Foundation ("MTF") [Member]	Dec. 31, 2009 Collaborative Arrangement [Member] Musculoskeletal Transplant Foundation ("MTF") [Member] Years	Dec. 31, 2012 Developed Technology [Member]
Foreign Currency Translation [Line Items]
Transactional foreign currency gains and (losses), including those generated from intercompany operations									$ 500,000	$ 1,600,000	$ 100,000
Weighted average amortization period ( in years)																				11 years
Number of reporting units									2
Period of agreement with MTF (in years)																			10
Extended Period of existing agreement with MTF (in years)															15
Marketing fee																46,500,000	36,800,000	29,700,000
Interest Expense														600,000
Advertising expense									300,000	500,000	600,000
Expenditures for research and development									28,577,000	22,861,000	27,958,000	3,000,000
Net Sales	$ 117,365,000	$ 107,857,000	$ 113,423,000	$ 108,936,000	$ 118,639,000	$ 111,510,000	$ 108,216,000	$ 103,606,000	$ 447,581,000	$ 441,971,000	$ 462,571,000		$ 55,000,000