Acquisition of Spinal Kinetics, Inc. - Summary of Preliminary Estimated Fair Values of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	8 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Apr. 30, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 72,401	$ 72,401		$ 53,565
Assigned Useful Life		9 years
Spinal Kinetics [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	6,785	$ 6,785	$ 6,785
Restricted cash	30	30	30
Accounts receivable	1,705	1,705	1,705
Inventories	8,175	8,175	8,175
Prepaid expenses and other current assets	315	315	315
Property, plant and equipment	2,285	2,285	2,285
Other long-term assets	320	320	320
In-process research and development ("IPR&D")	26,800	26,800	26,800
Deferred income taxes	2,374	2,374	3,483
Total identifiable assets acquired	61,289	61,289	62,398
Accounts payable	351	351	351
Other current liabilities	2,873	2,873	2,873
Other long-term liabilities	301	301	301
Total liabilities assumed	3,525	3,525	3,525
Goodwill	18,836	18,836	17,182
Total fair value of consideration transferred	76,600	$ 76,600	76,055
In-process research and development ("IPR&D"), Assigned Useful Life		Indefinite
Deferred income taxes, Adjustments	(1,109)
Total identifiable assets acquired, Adjustments	(1,109)
Goodwill, Adjustments	1,654
Total fair value of consideration transferred, Adjustments	545
Developed Technology [Member]
Business Acquisition [Line Items]
Assigned Useful Life		10 years
Developed Technology [Member] | Spinal Kinetics [Member]
Business Acquisition [Line Items]
Finite lived intangible assets acquired	12,400	$ 12,400	12,400
Assigned Useful Life		10 years
Tradename [Member]
Business Acquisition [Line Items]
Assigned Useful Life		9 years
Tradename [Member] | Spinal Kinetics [Member]
Business Acquisition [Line Items]
Finite lived intangible assets acquired	$ 100	$ 100	$ 100
Assigned Useful Life		2 years