SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Cash and Cash Equivalent [Abstract]
Cash, cash equivalents and restricted cash and time deposits	$ 757,373	$ 407,445
ACM Shanghai
Cash and Cash Equivalent [Abstract]
Cash payments for procurement of goods and services	13,683	21,285	$ 42,517
Payments of ordinary dividends, common stock	29,238	28,480	$ 19,200
United States
Cash and Cash Equivalent [Abstract]
Cash, cash equivalents and restricted cash and time deposits	107,184	56,308
Mainland China
Cash and Cash Equivalent [Abstract]
Cash, cash equivalents and restricted cash and time deposits	228,777	94,701
China Hong Kong
Cash and Cash Equivalent [Abstract]
Cash, cash equivalents and restricted cash and time deposits	421,104	255,853
South Korea
Cash and Cash Equivalent [Abstract]
Cash, cash equivalents and restricted cash and time deposits	241	516
Singapore
Cash and Cash Equivalent [Abstract]
Cash, cash equivalents and restricted cash and time deposits	$ 67	$ 67