Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating Activities
Net loss	$ (9,459)	$ (4,426)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation	307	42
Stock-based compensation expense	638	212
Loss on disposals of fixed assets	54
Decrease in
Prepaids and other current assets	63	63
Amortization of right-of-use asset, net	132
Accounts payable	413	21
Accrued expenses and other current liabilities	428	101
Net cash used in operating activities	(7,424)	(3,987)
Investing Activities
Purchases of property and equipment	(2,945)	(98)
Purchases of short-term investments	(4,649)	(3,639)
Proceeds from maturities of short-term investments	3,876
Purchases of other noncurrent assets		(64)
Net cash used in investing activities	(3,718)	(3,801)
Financing Activities
Issuance of common stock, net	94,059	10
Net cash provided by financing activities	94,059	10
Net increase (decrease) in cash and cash equivalents	82,917	(7,778)
Cash and cash equivalents at beginning of period	103,670	49,591
Cash and cash equivalents at end of period	186,587	$ 41,813
Supplemental Disclosures of Non-Cash Investing and Financing Activities
Unpaid purchases of property and equipment	313
Unpaid offering costs	$ 190