STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (33,737)	$ (22,799)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,688	1,677
Stock-based compensation	1,886	263
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(4,255)	(19)
Accounts payable	(622)	1,342
Accrued liabilities	2,460	847
Deferred rent	304	(44)
Deferred revenue	(4,347)	26,725
Net cash (used in) provided by operating activities	(35,623)	7,992
Cash flows from investing activities:
Purchase of property and equipment	(3,371)	(3,063)
Purchase of marketable securities	(300,552)
Net cash used in investing activities	(303,923)	(3,063)
Cash flows from financing activities:
Proceeds from public offering, net of issuance costs	238,384
Proceeds from issuance of preferred stock, net of issuance costs		122,223
Proceeds from other issuance of common stock	119	4
Proceeds from the term loan	4,540
Deferred financing costs		(410)
Payments of the term loan		(400)
Net cash provided by financing activities	243,043	121,417
Net (decrease) increase in cash, cash equivalents and restricted cash	(96,503)	126,346
Cash, cash equivalents and restricted cash—beginning of year	135,633	9,287
Cash, cash equivalents and restricted cash—end of year	39,130	135,633
Supplemental disclosures of cash flow information:
Cash paid for interest	191	25
Supplemental disclosures of noncash investing and financing activities:
Purchase of property and equipment included in accrued liabilities	73
Deferred financing costs included in accrued liabilities	1	$ 284
Conversion of convertible preferred stock into common stock	$ 162,223