SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for Bad Debts
Movement in Valuation Allowances and Reserves
Beginning Balance	$ 546	$ 445	$ 679
Additions	470	330	241
Charged (credit) to tax expense	0	0	0
Charged (credited) to retained earnings	0	0	0
Write-offs	(674)	(229)	(475)
Ending Balance	342	546	445
Allowance for Customer Credits
Movement in Valuation Allowances and Reserves
Beginning Balance	194	121	213
Additions	(26)	250	198
Charged (credit) to tax expense	0	0	0
Charged (credited) to retained earnings	0	0	0
Write-offs	(104)	(177)	(290)
Ending Balance	64	194	121
Tax Valuation Allowance
Movement in Valuation Allowances and Reserves
Beginning Balance	31,168	28,687	21,318
Additions	0	0	0
Charged (credit) to tax expense	(721)	2,481	7,369
Charged (credited) to retained earnings	0	0	0
Write-offs	0	0	0
Ending Balance	$ 30,447	$ 31,168	$ 28,687