Balance Sheet Detail - Accounts receivable - long term, net (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Balance Sheet Detail
Undiscounted cash flows June 30, 2022	$ 1,000
Undiscounted cash flows June 30, 2023	100
Undiscounted cash flows June 30, 2024	100
Accounts receivable - long term
Total amount due from customer	1,112	$ 1,853
Less unamortized discount	(21)	(49)
Less current portion included in accounts receivable	(975)	(1,500)
Total of accounts receivable, long term, net	$ 116	$ 304