Statements of Cash Flows (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash paid for interest	$ 828	$ 1,028
Cash paid for income taxes	3	18
Non-cash investing and financing activities
Inventory transferred to property and equipment	2,830	0
Change in accounts payable and accrued liabilities related to purchases of property and equipment	1,238	274
Release of repurchase rights on early exercised options	$ 0	$ 264