Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (57,410)	$ (53,281)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	455	457
Loss on disposal of property and equipment	3
Stock-based compensation expense	9,036	3,318
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(3,166)	(260)
Accounts receivable	134	359
Accounts payable	(361)	418
Accrued expenses and other liabilities	(778)	1,541
Net cash used in operating activities	(52,087)	(47,448)
Cash flows from investing activities:
Purchases of property and equipment	(43)	(407)
Proceeds from sale of property and equipment	4
Net cash used in investing activities	(39)	(407)
Cash flows from financing activities:
Payment of deferred issuance costs associated with Series B convertible preferred stock financing		(232)
Proceeds from stock options exercised	374	101
Proceeds from initial public offering, net of underwriters' discounts		109,517
Payment of deferred offering costs	(182)	(3,012)
Net cash provided by financing activities	192	106,374
Net (decrease) increase in cash, cash equivalents and restricted cash	(51,934)	58,519
Cash, cash equivalents and restricted cash, at beginning of period	151,128	92,609
Cash, cash equivalents and restricted cash, at end of period	99,194	$ 151,128
Supplemental disclosure of non-cash investing and financing activities:
Deferred offering costs not yet paid	70
Property and equipment in accounts payable	$ 11