Summary of Significant Accounting Policies - Narrative (Details) $ / shares in Units, $ in Thousands			3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 12, 2021 USD ($)	May 21, 2021 agreement	Sep. 30, 2021 USD ($) $ / shares	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($) $ / shares	Sep. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) $ / shares	Jan. 01, 2020 USD ($)
Cash and Cash Equivalents [Line Items]
Common stock, par value (in dollars per share) | $ / shares			$ 0.00001		$ 0.00001		$ 0.00001
Additional funding received in connection with business combination	$ 247,300
Restricted cash, current			$ 820		$ 820		$ 100
Restricted cash, non-current			313		313		415
Revenue recognized previously recorded as contract liability					1,600		2,600
Revenue recognized for cancelled contracts previously recorded as contract liability					300
Reduction in cost of revenue			(184)	$ 0	(135)	$ 0
Refund liability, current			1,400		1,400
Deferred fulfillment and prepaid launch costs			3,000		3,000		4,700
Number of launch agreements terminated | agreement		2
Impairment of prepaid launch costs					8,700
Operating right of use asset			7,846		7,846		316	$ 550
Operating lease liabilities			8,711		8,711		$ 326	$ 560
Cash Designated for Collateral
Cash and Cash Equivalents [Line Items]
Restricted cash			400		400
Restricted cash, current			100		100
Restricted cash, non-current			300		300
Cash Designated for Expenditures under National Security Agreement
Cash and Cash Equivalents [Line Items]
Restricted cash			$ 700		$ 700