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	$ 112,035	$ 114,752	$ 119,492	$ 116,041	$ 123,085	$ 117,306	$ 116,670	$ 113,060	$ 462,320	$ 470,121	$ 460,629
Spine Products Implants and Biologics [Member]
Product Type Reporting Information [Line Items]
Percent of Total Net Sales									32.00%	31.00%	29.00%
Net Sales									147,206	143,775	133,831
Spine Regenerative Stimulation [Member]
Product Type Reporting Information [Line Items]
Percent of Total Net Sales									35.00%	34.00%	38.00%
Net Sales									164,688	160,442	172,573
Spine [Member]
Product Type Reporting Information [Line Items]
Percent of Total Net Sales									67.00%	65.00%	67.00%
Net Sales									311,894	304,217	306,404
Orthopedics [Member]
Product Type Reporting Information [Line Items]
Percent of Total Net Sales									33.00%	35.00%	33.00%
Net Sales									$ 150,426	$ 165,904	$ 154,225