SURGICAL INSTRUMENTS - (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]
Surgical instruments	$ 72,018	$ 59,028
Less accumulated depreciation and allowances	(45,768)	(34,218)
Surgical instruments, net	26,250	24,810
Depreciation expense	$ 11,550	$ 8,161	$ 7,448