BUSINESS DEVELOPMENT - Asset Acquisition, Narrative (Details)				3 Months Ended			9 Months Ended		12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 09, 2019 USD ($) asset	Jan. 04, 2019 USD ($) asset	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Schedule Of Asset Acquisition [Line Items]
In-process research and development				$ 0	$ 59,889,000		$ 0	$ 59,889,000
Consortium of Focused Orthopedists, LLC | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Subsequent Event | Forecast | Smith & Nephew USD Limited
Schedule Of Asset Acquisition [Line Items]
Sale of Extremity Orthopedics business, product development payment	$ 41,500,000
Rebound
Schedule Of Asset Acquisition [Line Items]
Upfront payment		$ 67,100,000
Contingent development milestone payments commitment (up to)		$ 35,000,000.0
Number of assets acquired | asset		1
Remaining net assets acquired		$ 7,200,000
Development milestone									$ 5,000,000.0
In-process research and development									$ 5,000,000.0
Rebound | Cash and Cash Equivalents
Schedule Of Asset Acquisition [Line Items]
Remaining net assets acquired		2,100,000
Rebound | Deferred Tax Asset
Schedule Of Asset Acquisition [Line Items]
Remaining net assets acquired		4,200,000
Rebound | In-Process Research and Development Expense
Schedule Of Asset Acquisition [Line Items]
Upfront payment		$ 59,900,000
ISC
Schedule Of Asset Acquisition [Line Items]
Number of assets acquired | asset			1
Research and development						$ 1,700,000
ISC | Enabling technology license
Schedule Of Asset Acquisition [Line Items]
Upfront payment, intangible assets			$ 1,700,000
Option to acquire, period subsequent to first commercial sale			4 years
Maximum future purchase price, if circumstances met (not to exceed)			$ 80,000,000.0