INTANGIBLE ASSETS - Amortization Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 17,331	$ 15,993	$ 13,231
Research and development
Finite-Lived Intangible Assets [Line Items]
Amortization expense	327	328	697
Selling, general and administrative
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 17,004	$ 15,665	$ 12,534