STOCK-BASED COMPENSATION, Assumptions Used to Determine Fair Value of Share Options Granted (Details) - Employee Share Option [Member] - $ / shares		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Fair Value of Options Granted [Abstract]
Granted (in shares)		140,400	786,399	656,000
Service Period Based [Member]
Fair Value of Options Granted [Abstract]
Expected term in years	[1]	6 years 3 months		6 years 3 months
Expected dividend	[2]	0.00%	0.00%	0.00%
Service Period Based [Member] | Minimum [Member]
Fair Value of Options Granted [Abstract]
Fair value of common share (in dollars per share)	[3]	$ 38.38	$ 22.07	$ 13.64
Expected term in years	[1]		5 years 6 months
Volatility	[4]	48.53%	42.17%	39.91%
Risk-free interest rate	[5]	1.00%	0.44%	1.69%
Service Period Based [Member] | Maximum [Member]
Fair Value of Options Granted [Abstract]
Fair value of common share (in dollars per share)	[3]	$ 51.07	$ 85.27	$ 16.81
Expected term in years	[1]		6 years 3 months
Volatility	[4]	49.47%	48.15%	40.35%
Risk-free interest rate	[5]	1.44%	0.82%	2.46%
Market Based [Member]
Fair Value of Options Granted [Abstract]
Fair value of common share (in dollars per share)	[3]		$ 22.07
Volatility	[4]		45.10%
Risk-free interest rate	[5]		2.68%
Expected dividend	[6]		0.00%
Granted (in shares)		0
Market Based [Member] | Minimum [Member]
Fair Value of Options Granted [Abstract]
Expected term in years	[1]		9 years 2 months 12 days
Market Based [Member] | Maximum [Member]
Fair Value of Options Granted [Abstract]
Expected term in years	[1]		9 years 9 months 18 days

[1] 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.

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

[3] Fair value of Class A common stock value was the closing market price of the Class A common stock on the grant date.

[4] 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.

[5] 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.

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