Schedule II. - VALUATION AND QUALIFYING ACCOUNTS (Details) - Allowance for doubtful accounts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Valuation and Qualifying Accounts
Balance at beginning of year	$ 100	$ 245	$ 263
Charged to cost and expenses	159	189	93
Deductions	(148)	(334)	(111)
Balance at end of year	$ 111	$ 100	$ 245