CASH, CASH EQUIVALENTS AND SHORT-TERM INVESTMENTS - Summary of Changes in Fair Value of All Financial Liabilities (Details) - Contingent consideration - Level 3 - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value, beginning of the period	$ 1,613	$ 14,825	$ 14,971
Divestiture of Lazanda	0	(3,515)	0
Total	1,038	1,613	14,825
Royalties and milestone paid
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Royalties and milestone paid	(184)	(3,068)	(2,432)
Interest Expense.
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net accretion value adjustments	124	1,079	2,408
Selling, general and administrative expense
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net accretion value adjustments	$ (515)	$ (7,708)	$ (122)