Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
CASH FLOWS FROM OPERATING ACTIVITIES
Net loss	$ (11,886)	$ (5,362)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	1,237	215
Non-cash lease expense	54
Net amortization of premiums and discounts on short-term investments	(103)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	724	197
Accounts payable	588	(564)
Accrued expenses and other current liabilities	(1,931)	70
Net cash used in operating activities	(11,317)	(5,444)
CASH FLOWS FROM INVESTING ACTIVITIES
Purchase of short-term marketable securities	(24,781)
Proceeds from maturities of short-term marketable securities	18,500
Net cash used in investing activities	(6,281)
CASH FLOWS FROM FINANCING ACTIVITIES
Proceeds from the exercise of stock options	112
Proceeds from the disgorgment of stockholders' short-swing profits, net	52
Payment of initial public offering costs		(720)
Net cash provided by (used in) financing activities	164	(720)
Net decrease in cash, cash equivalents and restricted cash	(17,434)	(6,164)
Cash, cash equivalents and restricted cash at the beginning of the period	64,848	76,000
Cash, cash equivalents and restricted cash at the end of the period	47,414	69,836
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Net unrealizable gain on marketable securities	$ 51
Deferred offering costs included in accounts payable and accrued expenses and other current liabilities		$ 556