Business segment information - Business Segments by GBU (Detail) (USD $) In Thousands, unless otherwise specified	3 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	Dec. 31, 2011	Dec. 31, 2010
Product Type Reporting Information [Line Items]
Percent of Total Net Sales									100.00%	100.00%	100.00%
Net Sales	$ 117,365	$ 107,857	$ 113,423	$ 108,936	$ 118,639	$ 111,510	$ 108,216	$ 103,606	$ 447,581	$ 441,971	$ 462,571
Spine Repair Implants and Regenerative Biologics [Member]
Product Type Reporting Information [Line Items]
Percent of Total Net Sales									32.00%	28.00%	29.00%
Net Sales									142,829	124,415	132,938
Spine Regenerative Stimulation [Member]
Product Type Reporting Information [Line Items]
Percent of Total Net Sales									36.00%	37.00%	37.00%
Net Sales									159,289	160,946	172,574
Spine [Member]
Product Type Reporting Information [Line Items]
Percent of Total Net Sales									68.00%	65.00%	66.00%
Net Sales									302,118	285,361	305,512
Orthopedics [Member]
Product Type Reporting Information [Line Items]
Percent of Total Net Sales									32.00%	35.00%	34.00%
Net Sales									$ 145,463	$ 156,610	$ 157,059