Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating activities
Net loss	$ (36,647)	$ (34,137)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	1,275	1,092
Stock-based compensation expense	4,619	3,897
Net amortization of premiums and discounts on marketable securities	195	(86)
Changes in operating assets and liabilities:
Accounts receivable	2,000
Unbilled accounts receivable	(126)	(755)
Prepaid expenses and other current assets	1,773	1,079
Other assets	47	(17)
Accounts payable	622	1,436
Accrued expenses and other liabilities	397	9
Deferred revenue	(7,981)	(1,669)
Deferred rent and deferred lease incentive	(221)	(174)
Net cash used in operating activities	(34,047)	(29,325)
Investing activities
Purchases of marketable securities	(51,785)	(72,653)
Maturities of marketable securities	38,673	16,800
Purchases of property and equipment	(827)	(777)
Net cash used in investing activities	(13,939)	(56,630)
Financing activities
Proceeds from issuance of common stock in connection with private placement, net of placement agent fees and offering costs		64,368
Proceeds from issuance of common stock in connection with follow-on offering, net of issuance costs	47,407
Principal payments on capital lease obligations	(18)	(24)
Proceeds from issuance of common stock under benefit plans, net	324	809
Net cash provided by financing activities	47,713	64,960
Net decrease in cash, cash equivalents and restricted cash	(273)	(20,995)
Cash, cash equivalents, and restricted cash, beginning of period	58,144	97,805
Cash, cash equivalents, and restricted cash, end of period	57,871	76,810
Supplemental cash flow information
Cash paid for interest		1
Non-cash investing and financing activities:
Property and equipment purchases unpaid at end of period	59	54
Public offering costs unpaid at end of period		158
Cash and cash equivalents	56,779	75,718
Restricted cash	$ 1,092	1,092
IPO
Financing activities
Payment of initial public offering costs		$ (193)