REVENUE RECOGNITION (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Net product revenue	$ 68,217	$ 51,139	$ 170,241	$ 147,338
Bile acid products
Disaggregation of Revenue [Line Items]
Net product revenue	24,353	22,912	71,291	66,766
Tiopronin products
Disaggregation of Revenue [Line Items]
Net product revenue	29,821	28,227	84,907	80,572
Total net product sales
Disaggregation of Revenue [Line Items]
Net product revenue	$ 54,174	$ 51,139	$ 156,198	$ 147,338
Geographic Concentration Risk | Revenue from Contract with Customer | North America
Disaggregation of Revenue [Line Items]
Concentration risk, percentage			99.00%