Statements of Cash Flows (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash paid for interest	$ 681	$ 684
Cash paid for income taxes	3	6
Non-cash investing and financing activities
Accrued issuance costs	0	1,248
Inventory transferred to property and equipment	3,827	0
Change in accounts payable and accrued liabilities related to purchases of property and equipment	723	(69)
Release of repurchase rights on early exercised options	$ 0	$ 176