Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Operating activities
Net loss	$ (53,099)	$ (66,554)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	1,646	1,534
Stock-based compensation expense	5,673	2,950
In-process research and development expenses		25,591
Net amortization of premiums and discounts on marketable securities	(103)
Changes in operating assets and liabilities:
Unbilled accounts receivable	(592)
Prepaid expenses and other current assets	(1,126)	(2,714)
Other assets	(557)	(20)
Accounts payable	1,590	2,849
Accrued expenses and other liabilities	3,442	1,237
Deferred revenue	9,574
Deferred rent and deferred lease incentive	(277)	139
Net cash used in operating activities	(33,829)	(34,988)
Investing activities
Purchases of marketable securities	(81,270)
Maturities of marketable securities	39,600
Purchases of property and equipment	(870)	(745)
Transaction costs associated with asset acquisition		(91)
Net cash used in investing activities	(42,540)	(836)
Financing activities
Payment of stock issuance costs		(34)
Proceeds from initial public offering of common stock, net of underwriting discounts and commissions	(193)	64,443
Proceeds from issuance of common stock in connection with private placement, net of placement agent fees and offering costs	64,210
Principal payments on capital lease obligations	(37)	(34)
Proceeds from issuance of common stock under benefit plans, net	897	249
Net cash provided by financing activities	64,877	64,624
Net (decrease) increase in cash, cash equivalents and restricted cash	(11,492)	28,800
Cash, cash equivalents, and restricted cash, beginning of period	97,805	73,889
Cash, cash equivalents, and restricted cash, end of period	86,313	102,689
Supplemental cash flow information
Cash paid for interest	3	6
Non-cash investing and financing activities:
Acquisition of in process research and development through issuance of stock		25,500
Conversion of convertible preferred stock into common stock		165,136
Public offering costs unpaid at end of period		442
Cash and cash equivalents	85,221	101,597
Restricted cash	$ 1,092	$ 1,092