Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating activities
Net loss	$ (66,554)	$ (23,729)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	1,534	836
Stock-based compensation expense	2,950	1,397
In-process research and development expenses	25,591
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,714)	(29)
Other assets	(20)	20
Accounts payable	2,849	132
Accrued expenses and other liabilities	1,237	1,062
Deferred rent and deferred lease incentive	139	4,152
Net cash used in operating activities	(34,988)	(16,159)
Investing activities
Purchases of property and equipment	(745)	(5,515)
Transaction costs associated with asset acquisition	(91)
Net cash used in investing activities	(836)	(5,515)
Financing activities
Proceeds from initial public offering of common stock, net of underwriting discounts and commissions	64,443
Principal payments on capital lease obligations	(34)	(59)
Proceeds from issuance of common stock under benefit plans	249	18
Net cash provided by financing activities	64,624	105,115
Net increase in cash, cash equivalents and restricted cash	28,800	83,441
Cash, cash equivalents, and restricted cash, beginning of period	73,889	407
Cash, cash equivalents, and restricted cash, end of period	102,689	83,848
Supplemental cash flow information
Cash paid for interest	6	8
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
Property and equipment purchases unpaid at end of period		2,976
Public offering costs unpaid at end of period	442	73
Cash and cash equivalents	101,597	82,756
Restricted cash	1,092	1,092
Series A Convertible Preferred Stock
Financing activities
Proceeds from issuance of stock, net of issuance costs		25,322
Series B Convertible Preferred Stock
Financing activities
Proceeds from issuance of stock, net of issuance costs	$ (34)	$ 79,834