Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Operating activities
Net loss	$ (16,999)	$ (18,452)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	603	539
Stock-based compensation expense	2,073	1,693
Net amortization of premiums and discounts on marketable securities	74	(45)
Changes in operating assets and liabilities:
Accounts receivable	2,000
Unbilled accounts receivable	(1)	(325)
Prepaid expenses and other current assets	1,466	579
Other assets	15	(20)
Accounts payable	920	1,429
Accrued expenses and other liabilities	(2,016)	(91)
Deferred revenue	(4,258)	(425)
Deferred rent and deferred lease incentive	(103)	(86)
Net cash used in operating activities	(16,226)	(15,204)
Investing activities
Purchases of marketable securities	(2,997)	(55,837)
Maturities of marketable securities	15,674
Purchases of property and equipment	(262)	(567)
Net cash provided by (used in) investing activities	12,415	(56,404)
Financing activities
Proceeds from issuance of common stock in connection with follow-on offering, net of issuance costs	47,424
Principal payments on capital lease obligations	(13)	(12)
Proceeds from issuance of common stock under benefit plans, net	93	286
Net cash provided by financing activities	47,504	274
Net increase (decrease) in cash, cash equivalents and restricted cash	43,693	(71,334)
Cash, cash equivalents, and restricted cash, beginning of period	58,144	97,805
Cash, cash equivalents, and restricted cash, end of period	101,837	26,471
Supplemental cash flow information
Cash paid for interest		1
Non-cash investing and financing activities:
Property and equipment purchases unpaid at end of period	40	163
Public offering costs unpaid at end of period	18	301
Cash and cash equivalents	100,745	25,379
Restricted cash	$ 1,092	$ 1,092