Fair Value Measurements and Investments - Additional Information (Detail) - USD ($)				3 Months Ended		9 Months Ended
	Mar. 01, 2019	Feb. 14, 2019	Apr. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Feb. 06, 2019
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				$ 41,700,000		$ 41,700,000
Recognition of expense for contingent consideration				22,300,000		28,100,000
Spinal Kinetics [Member] | Other Current Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration				14,500,000		14,500,000
Spinal Kinetics [Member] | Other Long-term Liabilities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Contingent consideration				27,200,000		27,200,000
Maximum [Member] | Spinal Kinetics [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Future milestone payments			$ 60,000,000.0
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			15,000,000.0					$ 15,000,000.0
Payments obligation for contingent consideration		$ 15,000,000.0
Revenue Milestone [Member] | Spinal Kinetics [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Future milestone payments			$ 45,000,000.0
ENeura Restructured Debt Security [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Interest income				500,000	$ 0	1,500,000	$ 0
eNeura Inc [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Payments of restructured debt security				4,000,000.0
Adjusted carrying value of restructured debt				4,000,000.0		4,000,000.0
Other-than-temporary impairment on restructured debt securities				6,500,000
eNeura Inc [Member] | Reclassification Out of Accumulated Other Comprehensive Income [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Unrealized gains on restructured debt securities				$ 5,200,000		$ 5,200,000
eNeura Inc [Member] | Amended and Restated Senior Secured Promissory Note [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Debt maturity date						Mar. 04, 2019
Debt securities, maturity date description						Amended and Restated Senior Secured Promissory Note with eNeura (the “Restructured Debt Security”) to restructure the debt security, which extended the maturity date to the earlier of (i) March 4, 2022, (ii) the effective date of a change in control, or (iii) the effective date of an initial public offering by eNeura, and which also eliminated the conversion feature included within the original note.
Warrant exercisable price per share	$ 0.01
Warrant contractual term	10 years
Percentage of number of warrant issued equal to outstanding principal and accrued interest on debt security	10.00%
Debt security subject to certain anti-dilution provision price per share	$ 1.00
Equity Warrants [Member] | Bone Biologics Inc [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value of warrants						$ 0