Schedule II - Valuation and Qualifying Accounts - Schedule II (Details) - Allowance for doubtful accounts receivable: - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Beginning of Year	$ 45	$ 22	$ 149
Charged to expenses	(32)	23	(123)
Write offs	0	0	4
Balance at End of Year	$ 13	$ 45	$ 22