BUSINESS DEVELOPMENT - Asset Acquisition, Narrative (Details)			9 Months Ended
	Sep. 09, 2019 USD ($) asset	Jan. 04, 2019 USD ($) asset	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)
Schedule Of Asset Acquisition [Line Items]
Upfront payment, intangible assets			$ 64,995,000	$ 0
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
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 | Enabling technology license
Schedule Of Asset Acquisition [Line Items]
Number of assets acquired | asset		1
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