Fair Value Measurements and Investments - Additional Information (Detail) - USD ($) $ in Millions			9 Months Ended
	Oct. 25, 2019	Apr. 30, 2018	Sep. 30, 2020	Sep. 30, 2019
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Decrease in fair value of future net sales			$ 7.6
eNeura Inc [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Payments of restructured debt security	$ 4.0
Maximum borrowing capacity				$ 4.0
Other than temporary impairment losses	6.5
Unrealized gains included in accumulated other comprehensive income	$ 5.2
Spinal Kinetics [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Milestone achievement period		5 years	12 months
Contingent consideration			$ 35.1
Spinal Kinetics [Member] | Other Current Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration			14.7
Spinal Kinetics [Member] | Other Long-term Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration			$ 20.4
Maximum [Member] | Spinal Kinetics [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Future milestone payments		$ 60.0
US Food And Drug Administration [Member] | Spinal Kinetics [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Future milestone payments		15.0
Revenue Milestone [Member] | Spinal Kinetics [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Future milestone payments		$ 45.0