CONDENSED STATEMENTS OF CASH FLOWS - USD ($)	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net loss	$ (14,376,000)	$ (10,227,000)
Adjustments to reconcile net loss to net cash provided by (used) in operating activities:
Depreciation and amortization	1,145,000	763,000
Stock-based compensation	795,000	48,000
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(2,815,000)	(114,000)
Accounts payable	(493,000)	512,000
Accrued liabilities and other current liabilities	(182,000)	(707,000)
Deferred revenue	(1,759,000)	(35,000)
Net cash used in operating activities	(17,685,000)	(9,760,000)
Cash flows from investing activities:
Purchase of property and equipment	(2,067,000)	(853,000)
Net cash used in investing activities	(2,067,000)	(853,000)
Cash flows from financing activities:
Proceeds from initial public offering, net of issuance costs	77,264,000
Proceeds from issuance of preferred stock, net of issuance costs		31,000,000
Proceeds from issuance of common stock	43,000
Proceeds from the term loan	4,540,000
Payments of the term loan		(200,000)
Net cash provided by financing activities	81,847,000	30,800,000
Net increase in cash, cash equivalents and restricted cash	62,095,000	20,187,000
Cash, cash equivalents and restricted cash—beginning of year	135,633,000	9,287,000
Cash, cash equivalents and restricted cash—end of period	197,728,000	29,474,000
Supplemental disclosures of cash flow information:
Cash paid for interest	80,000	$ 12,000
Supplemental disclosures of noncash investing and financing activities:
Purchase of property and equipment included in accrued liabilities	75,000
Deferred financing costs in accrued liabilities	154,000
Conversion of convertible preferred stock into common stock	$ 162,223,000