Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021
Cash Flows from Operating Activities
Net loss	$ (290,574)	$ (242,922)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	64,513	50,661
Amortization of right of use asset	8,932	7,750
Depreciation and amortization	6,496	1,766
Accretion (amortization) of discounts and premiums on investments	1,128	5,177
Loss on write-off of fixed assets	314	0
Changes in assets and liabilities:
Prepaid expenses, other assets and long-term assets	(4,976)	517
Operating lease liabilities, net of tenant improvement allowance received	366	(5,389)
Accounts payable	4,327	(740)
Accrued expenses and other liabilities	(5,612)	9,088
Net cash used in operating activities	(215,086)	(174,092)
Cash Flows from Investing Activities
Maturities of investments	423,586	544,454
Purchase of investments	(150,189)	(583,654)
Purchase of property and equipment	(17,403)	(30,006)
Net cash provided by / (used in) investing activities	255,994	(69,206)
Cash Flows from Financing Activities
Tax payments related to shares withheld for vested restricted stock units	(2,649)	0
Proceeds from the issuance of common stock under employee stock purchase plan	582	970
Proceeds from the issuance of common stock upon exercise of options	1,642	29,992
Proceeds from the issuance of common stock, net	0	203,156
Proceeds from the issuance of debt	0	1,000
Net cash (used in) / provided by financing activities	(425)	235,118
Net increase in cash, cash equivalents and restricted cash	40,483	(8,180)
Cash, Cash Equivalents and Restricted Cash Beginning of Period	84,313	72,854
Cash, Cash Equivalents and Restricted Cash End of Period	124,796	64,674
Supplemental disclosure of non-cash investing and financing activities:
Net unrealized (loss) on investments	(1,437)	(24)
Acquisition of property and equipment included in accounts payable and accrued expenses	1,626	5,729
Conversion of convertible preferred stock to common stock	0	(1)
Lease liabilities arising from obtaining right-of-use asset from new leases	553	17,275
Lease liabilities arising from obtaining right-of-use asset from lease modifications	$ 7,664	$ 7,800