Commitments and Contingencies - Concentrations of Credit Risk (Details) $ in Thousands			3 Months Ended								6 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2020 USD ($) customer	Jul. 20, 2017 USD ($)	Dec. 31, 2020 USD ($) customer	Sep. 30, 2020 USD ($)	Jun. 30, 2020 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) customer	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2020 USD ($) customer	Dec. 31, 2019 USD ($) customer	Dec. 31, 2018 USD ($) customer
Customer Concentration
Restricted cash	$ 169,000		$ 169,000												$ 169,000
Letter of credit	152,400		152,400												152,400
Reduction in revenue		$ 10,900													399,700
Consolidated revenue			(309,099)	$ 107,048	$ 67,995	$ 40,819	$ 91,607	$ 59,392	$ 57,466	$ 21,510	$ 108,814	$ 78,976	$ 215,862	$ 138,368	(93,237)	$ 229,975	$ 174,215
Letter of Credit
Customer Concentration
Letter of credit	$ 500		$ 500												$ 500
Accounts receivable | Customer concentration | Customers
Customer Concentration
Number of customers | customer	3		3				2								3	2
Concentration risk (as a percent)															73.90%	62.60%
Revenues | Customer concentration | Customers
Customer Concentration
Number of customers | customer	2		2				2								2	2	2
Concentration risk (as a percent)															156.20%	49.70%	66.80%
Warrants issued with the Amazon, Inc transaction agreement
Customer Concentration
Reduction in revenue	$ 399,700														$ 420,000	$ 4,100	$ 9,800
Warrants issued with the Amazon, Inc transaction agreement | Revenues | Customer concentration | Amazon
Customer Concentration
Concentration risk (as a percent)															332.40%
Provision for common stock warrants															$ 420,000
Consolidated revenue															$ 310,100