ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Contract assets and liabilities (Details) - USD ($) $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Contract assets:
Unbilled receivables	$ 7,085	$ 5,968	$ 3,763
Contract liabilities:
Customer advances and unearned income	4,587	3,403	3,048
Unearned event income	$ 6,809	$ 3,831	$ 6,645