ACQUISITIONS - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended	109 Months Ended
	Nov. 19, 2021	Apr. 09, 2019	Dec. 31, 2021	Dec. 31, 2021	Dec. 31, 2030	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Contingent consideration			$ 0	$ 0		$ 14,736
Myoscience Acquisition
Business Acquisition [Line Items]
Consideration transferred		$ 147,500
Cash paid to acquire business				119,000
Contingent value right		$ 28,500
Maximum total payments for contingent consideration possible				100,000
Contingent consideration			43,000	43,000
Contingent consideration, payment terms		60 days
Flexion
Business Acquisition [Line Items]
Consideration transferred	$ 578,845
Cash paid to acquire business	533,604
Retirement of term loan	85,100
Contingent value right	45,241
Additional amount payable to holders of the CVRs	380,200
Flexion | Developed technologies
Business Acquisition [Line Items]
Finite-lived intangible assets acquired	$ 480,000
Useful life	9 years 8 months 12 days
Flexion | Developed technologies | Discount rates | Valuation, Income Approach
Business Acquisition [Line Items]
Discount rate, measurement input	17.50%
Flexion | Acquired IPR&D
Business Acquisition [Line Items]
Finite-lived intangible assets acquired	$ 60,000
Flexion | Acquired IPR&D | Discount rates | Valuation Technique, Discounted Cash Flow
Business Acquisition [Line Items]
Projected future cash flows discounted, rate	18.00%
Flexion | RSUs, In-The-Money Stock Options, and Common Stock
Business Acquisition [Line Items]
Cash paid to acquire business			448,500
Achievement of Regulatory Milestone
Business Acquisition [Line Items]
Acquisition-related contingent consideration			$ 12,000	$ 12,000		$ 15,000	$ 7,000
Achievement of ZILRETTA Sales of $250 Million
Business Acquisition [Line Items]
Contingent value right (in usd per share)	$ 1.00
Achievement of ZILRETTA Sales of $250 Million | Forecast
Business Acquisition [Line Items]
Annual product sales threshold					$ 250,000
Achievement of ZILRETTA Sales of $375 Million
Business Acquisition [Line Items]
Contingent value right (in usd per share)	2.00
Achievement of ZILRETTA Sales of $375 Million | Forecast
Business Acquisition [Line Items]
Annual product sales threshold					375,000
Achievement of ZILRETTA Sales of $500 Million
Business Acquisition [Line Items]
Contingent value right (in usd per share)	3.00
Achievement of ZILRETTA Sales of $500 Million | Forecast
Business Acquisition [Line Items]
Annual product sales threshold					$ 500,000
Achievement of FDA Approval of FX-201
Business Acquisition [Line Items]
Contingent value right (in usd per share)	1.00
Achievement of FDA Approval of FX-301
Business Acquisition [Line Items]
Contingent value right (in usd per share)	$ 1.00