SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Impairment for Equity Securities Without Readily Determinable Fair Values (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accounting Policies [Abstract]
Impairments and downward adjustments of equity securities without readily determinable fair values	$ 0	$ 0	$ 0	$ 2,958