ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 24,762	$ 21,845	$ 37,682
Credit card receivables	700	1,600
Cash and cash equivalents held in bank accounts in foreign countries	18,200	19,900
Restricted Cash, Current	943	1,514	1,514
Restricted Cash, Noncurrent	5,295	7,225	7,565
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	31,000	$ 30,584	$ 46,761
South Korea
Cash and Cash Equivalents [Line Items]
Net assets	$ 19,200