ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 7,731	$ 13,777	$ 24,185
Credit card receivables	1,400	1,900
Cash and cash equivalents held in bank accounts in foreign countries	3,500	11,300
Restricted Cash, Current	938	944	944
Restricted Cash, Noncurrent	718	476	503
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	9,387	$ 15,197	$ 25,632
GSX KOREA
Cash and Cash Equivalents [Line Items]
Net assets	$ 27,000