FAIR VALUE OF FINANCIAL INSTRUMENTS - Investments Valued Under the Measurement Alternative (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2018
Equity Securities without Readily Determinable Fair Value [Roll Forward]
Beginning balance, before cumulative impairment		$ 3,305	$ 11,205
Accumulated impairment as of January 1,		0	$ 0
Beginning balance, after cumulative impairment	$ 3,305	11,205
Removal of investment in connection with step acquisition	0	(9,700)
Acquisition of interest in a privately held company	0	1,800
Ending period balance	$ 3,305	$ 3,305