Commitment and Contingencies - Narratives (Details) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($) customer	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jul. 30, 2020 USD ($)	Apr. 26, 2017 ft²	Jun. 24, 2016 ft²
Operating Leased Assets [Line Items]
Additional number of square feet | ft²					18,000	45,000
Annual cost escalations, percentage	10.00%	10.00%
Rent expense		$ 914	$ 930
Provision for firm purchase commitments	$ 1,585	1,585	0
Number of customers entered into loan commitment | customer	1
Amount committed to lend	$ 1,000
Loan commitment on the consolidated balance sheet	100	100
Batteries
Operating Leased Assets [Line Items]
Non-cancellable purchase commitment	$ 2,504	2,504		$ 8,000
Purchases made		5,496
Cost of Sales
Operating Leased Assets [Line Items]
Rent expense		0	102
Research and Development Expense
Operating Leased Assets [Line Items]
Rent expense		713	430
General and Administrative Expense
Operating Leased Assets [Line Items]
Rent expense		$ 201	$ 398