EQUITY-BASED COMPENSATION - Equity-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Equity-based compensation expense
Total equity-based compensation expense		$ 18,533	$ 19,949	$ 20,296
Income tax effect		0	0	(6,188)
After-tax effect of equity-based compensation expense		18,533	19,949	14,108
Cost of product sales
Equity-based compensation expense
Total equity-based compensation expense		871	802	884
Research and development
Equity-based compensation expense
Total equity-based compensation expense		2,844	2,533	3,225
Selling, general and administrative
Equity-based compensation expense
Total equity-based compensation expense		$ 14,818	$ 16,614	$ 16,187
Restructuring Charges
Equity-based compensation expense
Total equity-based compensation expense	$ 700