Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash Flows from Operating Activities
Net loss	$ (63,328)	$ (47,371)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,805	1,218
Loss on disposal of property and equipment		7
Stock-based compensation	9,353	4,013
Preferred stock warrant liability revaluation		123
Accretion of discount on investments	(63)	(686)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,170)	(2,714)
Accounts payable	38	1,450
Accrued expenses	(93)	1,511
Other current liabilities	932	(11)
Deferred rent	3,952	141
Net cash used in operating activities	(48,574)	(42,319)
Cash Flows from Investing Activities
Purchase of property and equipment	(3,726)	(1,822)
Purchase of investments	(163,881)	(84,160)
Proceeds from maturities of investments	63,110	50,000
Change in deposits	127	92
Net cash used in investing activities	(104,370)	(35,890)
Cash Flows from Financing Activities
Proceeds from the issuance of common stock under the Employee Stock Purchase Plan	1,012	133
Proceeds from exercise of stock options	1,131	249
Proceeds from public offering, net	126,688	133,633
Principal payments on capital lease obligations	(35)	(36)
Payments of initial offering costs	(364)	(2,848)
Net cash provided by financing activities	128,432	131,131
Net change in cash, cash equivalents and restricted cash	(24,512)	52,922
Cash, cash equivalents and restricted cash, beginning of period	159,236	114,504
Cash, cash equivalents and restricted cash, end of period	134,724	167,426
Supplemental Disclosure of Cash Flow Information
Cash paid for interest	3	5
Cash paid for income taxes	1	1
Supplemental Schedule of Non-Cash Investing and Financing Activities
Costs related to public offering included in accounts payable and accrued liabilities	269
Conversion of redeemable convertible preferred stock to common stock		209,669
Reclassification of redeemable convertible preferred stock warrant liability to additional paid-in capital		503
Vesting of early exercised common stock options	4	$ 8
Purchases of property and equipment included in accounts payable and accrued liabilities	$ 91