Schedule II Valuation and Qualifying Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Allowance for doubtful accounts and returns
Changes in Valuation and Qualifying Accounts
Balance at Beginning of Period	$ 818
Charged to Costs and Expenses		$ 818
Deductions	818
Balance at End of Period		818
Deferred tax valuation allowance
Changes in Valuation and Qualifying Accounts
Balance at Beginning of Period	8,327	6,835	$ 7,136
Charged to Costs and Expenses	806	1,492	(441)
Deductions			(140)
Balance at End of Period	$ 9,133	$ 8,327	$ 6,835