STOCK-BASED COMPENSATION, Share Option Activities (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Weighed Average Remaining Contractual Term [Abstract]
Stock-based compensation expense	$ 5,117	$ 5,628	$ 3,572
Employee Share Option [Member]
Number of Option Share [Roll Forward]
Outstanding, beginning of period (in shares)	3,191,411	2,994,063	2,503,405
Granted (in shares)	140,400	786,399	656,000
Exercised (in shares)	(477,058)	(547,189)	(106,768)
Expired (in shares)			(2,757)
Forfeited/cancelled (in shares)	(54,004)	(41,862)	(55,817)
Outstanding, end of period (in shares)	2,800,749	3,191,411	2,994,063	2,503,405
Vested and exercisable (in shares)	1,922,180
Weighted Average Grant Date Fair Value [Abstract]
Outstanding at beginning of period (in dollars per share)	$ 5.13	$ 2.59	$ 0.91
Granted (in dollars per share)	48.16	12.17	6.29
Exercised (in dollars per share)	2.46	1.34	0.60
Expired (in dollars per share)			3.34
Forfeited/cancelled (in dollars per share)	24.97	4.80	2.38
Outstanding at end of period (in dollars per share)	7.36	5.13	2.59	$ 0.91
Weighted Average Exercise Price [Abstract]
Outstanding, beginning of period (in dollars per share)	12.73	6.77	4.09
Granted (in dollars per share)	106.15	29.17	16.21
Exercised (in dollars per share)	6.30	3.78	2.09
Expired (in dollars per share)			8.16
Forfeited/cancelled (in dollars per share)	57.10	12.65	6.23
Outstanding, end of period (in dollars per share)	$ 17.65	$ 12.73	$ 6.77	$ 4.09
Weighed Average Remaining Contractual Term [Abstract]
Outstanding weighed average remaining contractual term	6 years 6 months 10 days	7 years 1 month 17 days	7 years 18 days	7 years 3 months 18 days
Stock-based compensation expense	$ 4,674	$ 4,900	$ 2,265
Unrecognized employee stock-based compensation expense	$ 9,544	$ 8,733
Weighted-average period over which unrecognized compensation is expected to be recognized	1 year 7 months 9 days	1 year 10 months 20 days
Employee Share Option [Member] \| ACM Shanghai [Member]
Number of Option Share [Roll Forward]
Outstanding, beginning of period (in shares)	5,423,654	0
Granted (in shares)	0	5,869,808
Exercised (in shares)	0	0
Expired (in shares)	0	0
Forfeited/cancelled (in shares)	(46,154)	(446,154)
Outstanding, end of period (in shares)	5,377,500	5,423,654	0
Vested and exercisable (in shares)	0
Weighted Average Grant Date Fair Value [Abstract]
Outstanding at beginning of period (in dollars per share)	$ 0.23	$ 0
Granted (in dollars per share)	0	0.23
Exercised (in dollars per share)	0	0
Expired (in dollars per share)	0	0
Forfeited/cancelled (in dollars per share)	0.24	0.23
Outstanding at end of period (in dollars per share)	0.24	0.23	$ 0
Weighted Average Exercise Price [Abstract]
Outstanding, beginning of period (in dollars per share)	1.89	0
Granted (in dollars per share)	0	1.89
Exercised (in dollars per share)	0	0
Expired (in dollars per share)	0	0
Forfeited/cancelled (in dollars per share)	2.04	1.89
Outstanding, end of period (in dollars per share)	$ 2.04	$ 1.89	$ 0
Weighed Average Remaining Contractual Term [Abstract]
Outstanding weighed average remaining contractual term	2 years 6 months	3 years 6 months	0 years
Stock-based compensation expense	$ 349	$ 332	$ 0
Non-Employee Stock Option [Member]
Number of Option Share [Roll Forward]
Outstanding, beginning of period (in shares)	836,038	1,101,613	1,212,374
Granted (in shares)	0	20,000	0
Exercised (in shares)	(146,543)	(285,315)	(88,529)
Expired (in shares)	0	0	0
Forfeited/cancelled (in shares)	(489)	(260)	(22,232)
Outstanding, end of period (in shares)	689,006	836,038	1,101,613	1,212,374
Vested and exercisable (in shares)	677,756
Weighted Average Grant Date Fair Value [Abstract]
Outstanding at beginning of period (in dollars per share)	$ 1.02	$ 0.82	$ 0.78
Granted (in dollars per share)	0	10.29	0
Exercised (in dollars per share)	1.12	0.88	0.45
Expired (in dollars per share)	0	0	0
Forfeited/cancelled (in dollars per share)	0.34	0.30	0.55
Outstanding at end of period (in dollars per share)	1.00	1.02	0.82	$ 0.78
Weighted Average Exercise Price [Abstract]
Outstanding, beginning of period (in dollars per share)	3.07	2.69	2.57
Granted (in dollars per share)	0	25.60	0
Exercised (in dollars per share)	3.83	3.17	1.06
Expired (in dollars per share)	0	0	0
Forfeited/cancelled (in dollars per share)	0.84	0.75	3.00
Outstanding, end of period (in dollars per share)	$ 2.91	$ 3.07	$ 2.69	$ 2.57
Weighed Average Remaining Contractual Term [Abstract]
Outstanding weighed average remaining contractual term	3 years 11 months 23 days	4 years 11 months 1 day	5 years 10 months 6 days	6 years 7 months 28 days
Stock-based compensation expense	$ 94	$ 396	$ 1,307
Unrecognized employee stock-based compensation expense	$ 102	$ 195
Weighted-average period over which unrecognized compensation is expected to be recognized	21 days	1 month 2 days
Non-Employee Stock Option [Member] \| ACM Shanghai [Member]
Weighed Average Remaining Contractual Term [Abstract]
Unrecognized employee stock-based compensation expense	$ 525	$ 822
Weighted-average period over which unrecognized compensation is expected to be recognized	1 year 6 months	2 years 6 months

Weighted average grant-date fair value of non-vested options exercised.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.

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Gross number of share options (or share units) granted during the period.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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