Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net loss		$ (33,158)	$ (18,749)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense		390	66
Stock-based compensation expense		3,118	566
Amortization of deferred offering costs			22
Impairment loss of property and equipment			235
Deferred rent expense		(81)	(23)
Change in fair value of preferred stock warrant liability	$ 150		162
Change in fair value of derivative liability	1,042		1,629
Changes in operating assets and liabilities:
Prepaid expenses and other current assets		(4,121)	(768)
Other assets		(57)	(300)
Accounts payable		26	3,029
Accrued expenses and other current liabilities		(1,820)	(98)
Net cash used in operating activities		(35,703)	(14,229)
Cash flows from investing activities:
Change in restricted cash			24
Purchases of property and equipment		(741)	(424)
Net cash used in investing activities		(741)	(400)
Cash flows from financing activities:
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs			58,258
Proceeds from exercise of stock options		490
Proceeds from issuance of common shares upon completion of initial public offering costs, net of offering costs			105,423
Net cash provided by financing activities		490	163,681
Net (decrease) increase in cash, cash equivalents and restricted cash		(35,954)	149,052
Cash, cash equivalents and restricted cash at beginning of period		126,794	5,963
Cash, cash equivalents and restricted cash at end of period	155,015	90,840	155,015
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment included in accounts payable and accrued expenses		10	756
Property and equipment held for sale			19
Deferred offering costs included in accrued expenses		180	1,241
Purchase of property and equipment paid for by landlord			842
Accretion of issuance costs related to redeemable convertible preferred stock			2,240
Reconciliation of cash, cash equivalents and restricted cash reported within the condensed consolidated balance sheets:
Cash and cash equivalents	154,991	90,348	154,991
Long-term restricted cash (included in other assets)	24	492	24
Cash, cash equivalents and restricted cash at end of period	$ 155,015	$ 90,840	$ 155,015