ACCOUNTS RECEIVABLE - Allowance for doubtful accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
ACCOUNTS RECEIVABLE
Balance at beginning of year	$ 199
Provision for bad debt	377	$ 199
Uncollectible accounts written off	(76)
Balance at end of year	$ 500	$ 199