STOCK-BASED COMPENSATION, Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	$ 2,779	$ 1,557	$ 4,323	$ 2,919
Employee Stock Purchase Plan [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	2,651	1,329	3,717	1,841
Employee Stock Purchase Plan [Member] | ACM Shanghai [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	84	0	250	0
Non-Employee Stock Purchase Plan [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	44	228	356	1,078
Cost of Revenue [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	44	154	132	213
Sales and Marketing Expense [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	237	172	495	252
Research and Development Expense [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	193	759	568	939
General and Administrative Expense [Member]
Stock-based Compensation Expense [Abstract]
Stock-based compensation expense	$ 2,305	$ 472	$ 3,128	$ 1,515