Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (46,361)	$ (18,648)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	2,196	177
Depreciation and amortization expense	380	45
Amortization of deferred offering costs	37	24
Impairment loss of property and equipment	235
Deferred rent expense	(105)	134
Change in fair value of preferred stock warrant liability	162	17
Change in fair value of derivative liability	1,629	283
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(3,037)	(326)
Other assets	(115)	(218)
Accounts payable	2,018	176
Accrued expenses and other current liabilities	5,313	1,454
Other long-term liability		500
Net cash used in operating activities	(37,648)	(16,382)
Cash flows from investing activities:
Purchases of property and equipment	(1,832)	(383)
Net cash used in investing activities	(1,832)	(383)
Cash flows from financing activities:
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	58,257	17,415
Proceeds from issuance of common shares upon completion of initial public offering, net of offering costs	104,013
Payment of dilution liability	(2,000)
Exercise of stock option	17
Payments of issuance costs on debt facility		(44)
Net cash provided by financing activities	160,287	17,371
Net increase in cash and cash equivalents	120,807	606
Cash, cash equivalents and restricted cash at beginning of period	5,987	5,381
Cash, cash equivalents and restricted cash at end of period	126,794	5,987
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable and accrued expenses	256	11
Property and equipment held for sale	19
Issuance of warrants associated with debt facility		18
Deferred offering costs included in accrued expenses		85
Purchase of property and equipment paid for by landlord	842
Accretion of issuance costs related to redeemable convertible preferred stock	$ 2,243	$ 85