Condensed Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
OPERATING ACTIVITIES:
Net loss	$ (78,425)	$ (70,272)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	8,328	5,471
Amortization of operating lease right-of-use assets	308	281
Change in operating lease liability	(299)	(263)
Changes in operating assets and liabilities:
Financed insurance premium	(4,434)
Prepaid expenses	(1,107)	3,396
Accounts payable	8,530	(6,739)
Accrued expenses and other current liabilities	149	11,127
Amortization of leasehold improvements	1
Amortization of insurance premium	3,163	1,540
Net cash used in operating activities	(63,786)	(55,459)
INVESTING ACTIVITIES:
Purchase of available-for-sale securities	(109,119)	(127,558)
Proceeds from sale of available-for-sale securities	5,539	17,109
Proceeds from maturities of available-for-sale securities	104,206	62,536
Net cash used in investing activities	626	(47,913)
FINANCING ACTIVITIES:
Proceeds from stock issuance, net of cash issuance costs	74,420	134,102
Proceeds from financed insurance premium	4,434
Financed insurance premium down payment		(793)
Repayments of short-term borrowings	(3,534)	(1,074)
Exercise of stock options for common stock under Equity Incentive Plan	512	1,665
Exercise of Warrants	69
Net cash provided by financing activities	75,901	133,201
NET INCREASE (DECREASE) IN CASH AND CASH EQUIVALENTS	12,741	29,829
Cash and cash equivalents at beginning of period	57,466	18,850
Cash and cash equivalents at end of period	70,207	48,679
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Insurance premium obtained in exchange for a short-term loan		(4,015)
Unrealized gain (loss) on marketable securities	$ (142)	92
Private Placement
FINANCING ACTIVITIES:
Payment of offering costs		(206)
Registration of Form S-3 offering/Shelf Offering
FINANCING ACTIVITIES:
Payment of offering costs		(493)
SUPPLEMENTAL DISCLOSURE OF CASH FLOW INFORMATION:
Stock issuance costs in accrued expenses		$ 2