ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 22,207	$ 24,762	$ 21,845
Credit card receivables	2,400	700
Cash and cash equivalents held in bank accounts in foreign countries	18,600	18,200
Restricted Cash, Current	944	943	1,514
Restricted Cash, Noncurrent	4,346	5,295	7,225
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	27,497	$ 31,000	$ 30,584
South Korea
Cash and Cash Equivalents [Line Items]
Net assets	$ 21,000