Fair Value Measurements (Tables)

9 Months Ended

Sep. 30, 2021

Fair Value Disclosures [Abstract]

Summary of Fair Value Measurements for Items

The following table presents a summary of fair value measurements for financial instruments as of September 30, 2021, and December 31, 2020, respectively:

September 30, 2021	Level 1		Level 2		Level 3		Total fair value
	(in thousands)
U.S. government and government agencies	$	—	$	167,325	$	—	$	167,325
Total assets at fair value	$	—	$	167,325	$	—	$	167,325

December 31, 2020	Level 1		Level 2		Level 3		Total fair value
	(in thousands)
U.S. government and government agencies	$	—	$	53,963	$	—	$	53,963
Total assets at fair value	$	—	$	53,963	$	—	$	53,963
Derivative liabilities	$	—	$	—	$	44,810	$	44,810
Warrants payable	—		—		97,782		97,782
Total liabilities at fair value	$	—	$	—	$	142,592	$	142,592

Schedule of Significant Unobservable Inputs Used in Black-Scholes Model to Measure Warrants Payable

The significant unobservable inputs used in the Black-Scholes model to measure the warrants payable that are categorized within Level 3 of the fair value hierarchy, as of the year ended December 31, 2020, are as follows:

December 31, 2020	Preferred stock purchase warrants	Common stock purchase warrants
Beginning stock price	N/A	$	30.14
Strike price	N/A	1.04
Expected volatility	N/A	56.0		%
Expected term	N/A	0.02 years
Risk-free interest rate	N/A	0.09		%
Discount factor	N/A	13.0

Schedule of Changes in Balances of Level 3 Financial Liabilities

The changes in balances of Level 3 financial liabilities during the three months ended September 30, 2020, and the nine months ended September 30, 2021 and 2020, respectively, are as follows:

	Convertible securities		Derivative liabilities		Warrants payable		Total
	(in thousands)
Balance, June 30, 2020	$	285,166	$	119,167	$	29,424	$	433,757
Issuances	—		—		—		—
Settlements	—		—		—		—
Transfers in	—		—		—		—
Transfers out	—		—		—		—
Total realized losses (gains)	95,477		(68,081)		19,978		47,374
Balance, September 30, 2020	$	380,643	$	51,086	$	49,402	$	481,131

	Convertible securities		Derivative liabilities		Warrants payable		Total
	(in thousands)
Balance, December 31, 2020	$	949,553	$	44,810	$	97,782	$	1,092,145
Issuances	—		—		—		—
Settlements	(949,553)		(44,810)		(97,782)		(1,092,145)
Transfers in	—		—		—		—
Transfers out	—		—		—		—
Total realized losses (gains)	—		—		—		—
Balance, September 30, 2021	$	—	$	—	$	—	$	—

	Convertible securities		Derivative liabilities		Warrants payable		Total
	(in thousands)
Balance, December 31, 2019	$	251,885	$	138,561	$	17,672	$	408,118
Issuances	—		—		—		—
Settlements	—		—		—		—
Transfers in	—		—		—		—
Transfers out	—		—		—		—
Total realized losses (gains)	128,758		(87,475)		31,730		73,013
Balance, September 30, 2020	$	380,643	$	51,086	$	49,402	$	481,131

Schedule of Changes in Fair Value of Warrants Payable

The following table presents the changes in the fair value of warrants payable:

September 30, 2021	Public and Private Placement Warrants
	(in thousands)
Initial measurement, January 7, 2021	$	147,582
Mark-to-market adjustment	(66,214)
Warrants exercised	(81,283)
Warrants redeemed	(85)
Warrants payable balance, September 30, 2021	$	—