Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash Flows from Operating Activities
Net loss	$ (47,371)	$ (25,956)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,218	1,027
Loss on disposal of property and equipment	7	1
Stock-based compensation	4,013	832
Preferred stock warrant liability revaluation	123	30
Accretion of discount on investments	(686)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(2,714)	(61)
Accounts payable	1,450	508
Accrued expenses	1,511	(328)
Other current liabilities	(11)	205
Deferred rent	141	16
Net cash used in operating activities	(42,319)	(23,726)
Cash Flows from Investing Activities
Purchase of property and equipment	(1,822)	(1,326)
Purchase of investments	(84,160)
Proceeds from maturities of investments	50,000	22,397
Change in deposits	92	(3)
Net cash provided by (used in) investing activities	(35,890)	21,068
Cash Flows from Financing Activities
Proceeds from issuance of convertible preferred stock, net		120,312
Proceeds from the issuance of common stock under the Employee Stock Purchase Plan	133
Proceeds from exercise of stock options	249	30
Proceeds from initial public offering, net	133,633
Principal payments on capital lease obligations	(36)	(40)
Payments of initial offering costs	(2,848)
Net cash provided by financing activities	131,131	120,302
Net change in cash, cash equivalents and restricted cash	52,922	117,644
Cash, cash equivalents and restricted cash, beginning of period	114,504	8,242
Cash, cash equivalents and restricted cash, end of period	167,426	125,886
Supplemental Disclosure of Cash Flow Information
Cash paid for interest	5	7
Cash paid for income taxes	1	$ 1
Supplemental Schedule of Non-Cash Investing and Financing Activities
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	$ 8