Quarterly Financial Information (Unaudited) - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2017
Effect Of Fourth Quarter Events [Line Items]
Income tax benefit related to 2017 Tax Act	$ 1,272.4
Goodwill impairment charge				$ 304.7
Income tax expense (benefit) related to previous periods		$ 13.0	$ (21.0)
Pre-tax operating expenses			$ 12.2
Product Category Operating Segments [Member] | Spine [Member]
Effect Of Fourth Quarter Events [Line Items]
Goodwill impairment charge	$ 272.0