STOCK-BASED COMPENSATION - Stock-based compensation expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allocated Share-based Compensation Expense	$ 9,100	$ 6,700	$ 6,100
Employee Stock Purchase Plan 2016 [Member]
Allocated Share-based Compensation Expense	147	102	68
Stock Incentive Plan 2008 [Member]
Allocated Share-based Compensation Expense	9,070	6,680	6,022
Cost of sales [Member] | Employee Stock Purchase Plan 2016 [Member]
Allocated Share-based Compensation Expense	18	11	6
Cost of sales [Member] | Stock Incentive Plan 2008 [Member]
Allocated Share-based Compensation Expense	101	87	86
Research and development Expense [Member] | Employee Stock Purchase Plan 2016 [Member]
Allocated Share-based Compensation Expense	29	16	1
Research and development Expense [Member] | Stock Incentive Plan 2008 [Member]
Allocated Share-based Compensation Expense	756	771	677
Selling, general and administrative Expenses [Member] | Employee Stock Purchase Plan 2016 [Member]
Allocated Share-based Compensation Expense	100	75	61
Selling, general and administrative Expenses [Member] | Stock Incentive Plan 2008 [Member]
Allocated Share-based Compensation Expense	$ 8,213	$ 5,822	$ 5,259