Condensed Statements of Cash Flows - USD ($)	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities
Net loss	$ (22,506,000)	$ (42,800,000)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	963,000	823,000
Stock-based compensation expense	2,380,000	1,298,000
Changes in operating assets and liabilities:
Tax credit receivable	250,000	(20,000)
Accounts receivable	(79,000)
Prepaid expenses and other current assets	(4,774,000)	(1,321,000)
Other non-current assets	(70,000)	(88,000)
Accounts payable	1,826,000	212,000
Accrued liabilities	1,228,000	2,357,000
Other long-term liabilities	(4,000)	45,000
Net cash used in operating activities	(20,786,000)	(39,494,000)
Cash flows from investing activities
Purchase of short-term investments	(267,818,000)	(34,751,000)
Maturity of short-term investments	45,997,000	27,023,000
Accretion of short-term investments	(6,000)	(242,000)
Purchase of property and equipment	(945,000)	(780,000)
Net cash used in investing activities	(222,772,000)	(8,750,000)
Cash flows from financing activities
Proceeds from issuance of common stock upon initial public offering, net of issuance costs	150,751,000
Proceeds from issuance of common stock upon completion of private placement	10,000,000
Proceeds from exercise of stock options	205,000
Proceeds from issuance of restricted common stock		146,000
Payment of deferred offering costs		(1,438,000)
Net cash provided by/(used) in financing activities	212,975,000	(1,292,000)
Net decrease in cash and cash equivalents	(30,583,000)	(49,536,000)
Cash and cash equivalents at beginning of period	85,807,000	60,949,000
Cash and cash equivalents at end of period	55,224,000	11,413,000
Supplemental disclosures of noncash investing and financing activities:
Purchase of property and equipment in accounts payable and accrued liabilities	242,000
Reclassification of restricted stock awards from liabilities to common stock upon vesting	9,000	24,000
Accretion to redemption value and cumulative dividends on redeemable convertible preferred stock		4,078,000
Deferred offering costs in accounts payable and accrued liabilities		1,152,000
Net unrealized (loss) gain on short-term investments	(17,000)	$ 1,000
Series C Preferred Stock [Member]
Cash flows from financing activities
Proceeds from issuance of Series C preferred stock, net of issuance costs	$ 52,019,000