Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash Flows from Operating Activities
Net loss	$ (20,418)	$ (13,579)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	541	397
Loss on disposal of property and equipment		5
Stock-based compensation	2,482	776
Preferred stock warrant liability revaluation		50
Accretion of discount on investments	(80)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	356	(562)
Accounts payable	(79)	716
Accrued expenses	(3,020)	(993)
Other current liabilities	1,124	225
Other non-current liabilities	505
Deferred rent	675	(12)
Net cash used in operating activities	(17,914)	(12,977)
Cash Flows from Investing Activities
Purchase of property and equipment	(523)	(166)
Purchase of investments	(58,974)	(74,314)
Proceeds from maturities of investments	10,570
Change in deposits	127	52
Net cash used in investing activities	(48,800)	(74,428)
Cash Flows from Financing Activities
Proceeds from the issuance of common stock under the Employee Stock Purchase Plan	533
Proceeds from exercise of stock options	423	13
Principal payments on capital lease obligations	(13)	(12)
Payments of initial offering costs		(57)
Net cash provided by (used in) financing activities	943	(56)
Net change in cash, cash equivalents and restricted cash	(65,771)	(87,461)
Cash, cash equivalents and restricted cash, beginning of period	159,236	114,504
Cash, cash equivalents and restricted cash, end of period	93,465	27,043
Supplemental Disclosure of Cash Flow Information
Cash paid for interest	1	2
Cash paid for income taxes		1
Supplemental Schedule of Non-Cash Investing and Financing Activities
Vesting of early exercised common stock options	$ 4
Purchases of property and equipment included in accounts payable and accrued liabilities		879
Deferred offering costs included in accounts payable and accrued expenses		$ 223