Warrant Transaction Agreements - Amazon.com, Inc. Transaction Agreement (Details) $ / shares in Units, $ in Thousands					1 Months Ended	3 Months Ended			6 Months Ended		12 Months Ended
	Dec. 31, 2020 USD ($) $ / shares shares	Nov. 02, 2020 USD ($) installment $ / shares shares	Jan. 01, 2019 USD ($) installment shares	Apr. 04, 2017 USD ($) shares	Jul. 31, 2021 shares	Jun. 30, 2021 USD ($) $ / shares shares	Mar. 31, 2021 shares	Jun. 30, 2020 USD ($)	Jun. 30, 2021 USD ($) $ / shares shares	Jun. 30, 2020 USD ($)	Dec. 31, 2020 USD ($) $ / shares shares	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Class of Warrant or Right [Line Items]
Number of warrants exercised (in shares) | shares							16,489,014
Selling, general and administrative						$ 38,652		$ 21,644	$ 64,231	$ 32,753
Provision for loss contracts related to service									(4,399)	(277)
Risk-free interest rate	0.58%	0.58%									0.58%
Volatility	75.00%	75.00%									75.00%
Expected average term		6 years 5 months 1 day									6 years 3 months 3 days
Exercise price | $ / shares	$ 13.81	$ 13.81									$ 13.81
Stock price | $ / shares	$ 33.91	15.47									$ 33.91
Warrant Transaction Agreements
Class of Warrant or Right [Line Items]
Shares of common stock that can be purchased from warrants issued (in shares) | shares				55,286,696
Reduction in revenue						$ 105		$ 3,400	$ 209	$ 4,700
Number of warrants exercised (in shares) | shares					3,501,640	4,745,905	9,214,449		13,960,354
Warrant shares vested (in shares) | shares	55,286,696										55,286,696
Fair value of warrants per share | $ / shares		$ 10.57									$ 26.95
Tranche one of warrants issued with the Amazon.com, Inc transaction agreement
Class of Warrant or Right [Line Items]
Shares of common stock that can be purchased from warrants issued (in shares) | shares				5,819,652
Cash payments to be received under agreement				$ 600,000
Selling, general and administrative				$ 6,700
Exercise price calculation									$1.1893
Tranche two of warrants issued with the Amazon.com, Inc. Transaction Agreement
Class of Warrant or Right [Line Items]
Cash payments to be received under agreement			$ 50,000
Reduction in revenue											$ 9,000	$ 4,100	$ 9,800
Warrant shares vested (in shares) | shares			29,098,260
Number of installments | installment			4
Tranche two of warrants issued with the Amazon.com, Inc. Transaction Agreement | Maximum
Class of Warrant or Right [Line Items]
Cash payments to be received under agreement			$ 200,000
Tranche three of warrants issued with the Amazon.com, Inc. Transaction Agreement
Class of Warrant or Right [Line Items]
Cash payments to be received under agreement		$ 50,000
Reduction in revenue	$ 399,700										24,100
Warrant shares vested (in shares) | shares		20,368,784
Number of installments | installment		8
Exercise price of warrants (in dollars per share) | $ / shares						$ 13.81			$ 13.81
Fair value of warrants per share | $ / shares		$ 10.57
Warrant percentage weighted average share price									90.00%
Tranche three of warrants issued with the Amazon.com, Inc. Transaction Agreement | Maximum
Class of Warrant or Right [Line Items]
Cash payments to be received under agreement		$ 400,000
Warrant Issued With Amazon
Class of Warrant or Right [Line Items]
Reduction in revenue											$ 399,700
Warrant shares vested (in shares) | shares	5,354,905	12,730,490									5,354,905
Provision for loss contracts related to service											$ 12,800