ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Investments (Details)	12 Months Ended
	Dec. 31, 2018 USD ($) investment	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of long-term investments | investment	2
Payment, long-term investment	$ 3,000,000	$ 0	$ 0
Loans receivable, recoverable cost	3,000,000
Loans receivable, impairment	$ 0