BALANCE SHEETS COMPONENTS - Prepaid expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Prepaid expenses
Engineering, design, and testing	$ 14,871	$ 8,016
Software subscriptions	4,531	1,875
Prepayments for Arizona manufacturing equipment	80	13,895
Vehicle engineering	20	4,855
Other	2,338	969
Total prepaid expenses	$ 21,840	$ 29,610

Amount of asset related to consideration paid in advance for costs that provide economic benefits within a future period of one year or the normal operating cycle, if longer.

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Name:	us-gaap_PrepaidExpenseCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant