FAIR VALUE MEASUREMENT AND FINANCIAL INSTRUMENTS - Summary of Changes in Fair Value of Contingent Consideration (Details) $ in Thousands	3 Months Ended
	Dec. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 95,000	$ 91,400	$ 47,400	$ 48,400
Change in fair value included in loss	25,020	3,600	44,000	(1,000)
Ending balance	120,020	95,000	91,400	$ 47,400
Change in fair value of contingent consideration	$ 25,000	$ 3,600	$ 44,000
Discount Rate | Minimum
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Contingent consideration liability, measurement input	0.056				0.066
Discount Rate | Maximum
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Contingent consideration liability, measurement input	0.118				0.137
Royalty Rate
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Contingent consideration liability, measurement input	0.02