SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES, Basic and Diluted Net Income per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Numerator [Abstract]
Net income	$ 42,921	$ 21,677	$ 19,458
Less: Net income attributable to non-controlling interests and redeemable non-controlling interests	5,164	2,897	564
Net income available to common stockholders, basic	37,757	18,780	18,894
Less: Dilutive effect arising from share-based awards by ACM Shanghai	108	0	0
Net income available to common stockholders, diluted	$ 37,649	$ 18,780	$ 18,894
Weighted average shares outstanding, basic (in shares)	19,218,236	18,233,361	16,800,623
Effect of dilutive securities (in shares)	2,567,336	2,950,108	2,334,874
Weighted average shares outstanding, diluted (in shares)	21,785,572	21,183,469	19,135,497
Net income per common share [Abstract]
Basic (in dollars per share)	$ 1.96	$ 1.03	$ 1.12
Diluted (in dollars per share)	$ 1.73	$ 0.89	$ 0.99
Anti-dilutive securities excluded from earnings per share (in shares)	98,800	78,000	606,000