Acquisition of Spinal Kinetics, Inc. - Summary of Preliminary Estimated Fair Values of Assets Acquired and Liabilities Assumed (Detail) - USD ($) $ in Thousands	Apr. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill		$ 70,747	$ 53,565
Spinal Kinetics [Member]
Business Acquisition [Line Items]
Cash and cash equivalents	$ 6,785
Restricted cash	30
Accounts receivable	1,705
Inventories	8,175
Prepaid expenses and other current assets	315
Property, plant and equipment	2,285
Other long-term assets	320
In-process research and development ("IPR&D")	26,800
Deferred income taxes	3,483
Total identifiable assets acquired	62,398
Accounts payable	351
Other current liabilities	2,873
Other long-term liabilities	301
Total liabilities assumed	3,525
Goodwill	17,182
Total fair value of consideration transferred	$ 76,055
In-process research and development ("IPR&D"), Assigned Useful Life	Indefinite
Developed Technology [Member] | Spinal Kinetics [Member]
Business Acquisition [Line Items]
Finite lived intangible assets acquired	$ 12,400
Assigned Useful Life	10 years
Tradename [Member] | Spinal Kinetics [Member]
Business Acquisition [Line Items]
Finite lived intangible assets acquired	$ 100
Assigned Useful Life	2 years