FINANCIAL LIABILITY CARRIED AT FAIR VALUE (Details) $ / shares in Units, ¥ in Thousands, $ in Thousands			1 Months Ended				3 Months Ended		9 Months Ended
		Jul. 29, 2020 USD ($) $ / shares shares	Apr. 30, 2020 USD ($) Agreement shares	Aug. 31, 2019 USD ($) $ / shares shares	Mar. 31, 2018 USD ($) shares	Mar. 31, 2017 USD ($) $ / shares shares	Sep. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2019 USD ($)	Sep. 30, 2020 USD ($) $ / shares shares	Sep. 30, 2019 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2016 CNY (¥)
Related Party Transaction [Abstract]
Shares issued value								$ 26,463		$ 26,463
Change in fair value of financial liability							$ 6,533	$ 0	$ 11,964	$ 0
SMC 2020 Warrants [Member]
Related Party Transaction [Abstract]
Financial liability carried at fair value		$ 21,679
Change in fair value of financial liability							6,533		11,964
Fair value warrant amount							$ 21,679		$ 21,679
Fair Value of Options Granted [Abstract]
Fair value of common share (in dollars per share) | $ / shares	[1]						$ 89.28		$ 89.28
Expected term	[2]								3 years 5 months 1 day
Volatility	[3]								47.42%
Expected dividend	[4]								0.15%
Risk-free interest rate	[5]								0.00%
Common Class A [Member]
Fair Value of Options Granted [Abstract]
Fair value of common share (in dollars per share) | $ / shares				$ 13.195
Common Class A [Member] | SMC 2020 Warrants [Member]
Related Party Transaction [Abstract]
Shares issued (in shares) | shares		242,681
Fair Value of Options Granted [Abstract]
Fair value of common share (in dollars per share) | $ / shares		$ 7.50
ACM Shanghai [Member]
Related Party Transaction [Abstract]
Repayments of notes				$ 1,161
Number of agreement | Agreement			2
ACM Shanghai [Member] | Senior Secured Promissory Note [Member]
Related Party Transaction [Abstract]
Receivables			$ 1,820
ACM Shanghai [Member] | Intercompany Note [Member]
Related Party Transaction [Abstract]
Promissory note principal amount					$ 2,981
Interest rate on promissory note					3.01%
Promissory note maturity date									Aug. 17, 2023
Fair value warrant amount			$ 1,820
SMC [Member]
Related Party Transaction [Abstract]
Payment for investment											$ 2,981	¥ 20,123,500
Investment repayment period									60 days
Number of shares repurchased/surrender in exchange (in shares) | shares			242,681	154,821
Repayments of notes				$ 882
Investment due amount				$ 1,820
Consideration price in fair value			$ 9,715
Fair Value of Options Granted [Abstract]
Fair value of common share (in dollars per share) | $ / shares				$ 13.195
SMC [Member] | Senior Secured Promissory Note [Member]
Related Party Transaction [Abstract]
Promissory note principal amount					$ 2,981
Interest rate on promissory note					3.01%
Promissory note maturity date									Aug. 17, 2023
SMC [Member] | Common Class A [Member]
Related Party Transaction [Abstract]
Shares issued (in shares) | shares						397,502
Shares issued value						$ 2,981
Number of shares repurchased/surrender in exchange (in shares) | shares							242,681		242,681
Fair Value of Options Granted [Abstract]
Fair value of common share (in dollars per share) | $ / shares						$ 7.50
SMC [Member] | Common Class A [Member] | Senior Secured Promissory Note [Member]
Related Party Transaction [Abstract]
Exercise of common stock warrant issued (in shares) | shares					397,502
SMC [Member] | ACM Shanghai [Member]
Related Party Transaction [Abstract]
Repayment of investment in cash			$ 1,820	$ 1,161

[1] Fair value of Class A common stock was the closing market price of the Class A common stock on July 29, 2020.

[2] Expected term of share options is based on the average of the vesting period and the contractual term for each grant according to Staff Accounting Bulletin 110.

[3] Volatility is calculated based on the historical volatility of the stock of companies comparable to ACM in the period equal to the expected term of each grant.

[4] Risk-free interest rate is based on the yields of U.S. Treasury securities with maturities similar to the expected term of the share options in effect at the time of grant.

[5] Expected dividend is assumed to be 0% as ACM has no history or expectation of paying a dividend on its common stock.