Business segment information - Operating Income (Loss) 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]
Operating income (loss)	$ 25,613	$ 18,805	$ 14,298	$ 17,920	$ 8,174	$ 20,967	$ 12,359	$ (35,600)	$ 76,636	$ 5,900	$ 65,984
Spine [Member]
Product Type Reporting Information [Line Items]
Operating income (loss)									80,528	31,173	78,451
Orthopedics [Member]
Product Type Reporting Information [Line Items]
Operating income (loss)									13,197	3,779	7,847
Corporate [Member]
Product Type Reporting Information [Line Items]
Operating income (loss)									$ (17,089)	$ (29,052)	$ (20,314)