Acquisition of Spinal Kinetics, Inc. - Summary of Unaudited Pro forma Results (Detail) - Spinal Kinetics [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition [Line Items]
Net sales	$ 111,708	$ 109,019	$ 336,882	$ 328,182
Net income from continuing operations	$ 78	$ 1,415	$ 7,055	$ 448