Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities:
Net loss	$ (23,450)	$ (7,414)
Adjustments to reconcile net loss to net cash used in operating activities:
Amortization of discount on marketable securities	(57)
Depreciation and amortization expense	31
Stock-based compensation expense	1,583	210
Expense related to acquisition of intellectual property (see Note 6)		3,157
Changes in operating assets and liabilities:
Restricted cash	(84)
Prepaid expenses and other current assets	(1,573)	(532)
Accounts payable	3,119	2,247
Accrued liabilities	2,819	193
Funding advance	500
Other liabilities	25
Net cash used in operating activities	(17,087)	(2,139)
Investing activities:
Purchases of property and equipment	(304)	(51)
Purchases of marketable securities	(74,543)
Net cash used in investing activities	(74,847)	(51)
Financing activities:
Proceeds from issuance of Series A redeemable convertible preferred stock		5,500
Proceeds from initial public offering, net of issuance costs	89,938
Net cash provided by financing activities	89,938	5,500
Net (decrease) increase in cash and cash equivalents	(1,996)	3,310
Cash and cash equivalents at beginning of period	53,349
Cash and cash equivalents at end of period	51,353	$ 3,310
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable	12
Conversion of redeemable convertible preferred stock into common stock	$ 81,620