CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net loss	$ (1,073)	$ (35,331)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	2,080	1,907
Noncash lease expense	279	221
Stock-based compensation expense	3,883	2,883
Accretion of discount (amortization of premium) on short-term investments	162	(175)
Loss on disposal of property and equipment	6
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(870)	1,087
Accounts payable	(100)	4,841
Accrued expenses and other liabilities	(4,540)	(535)
Deferred revenue	(29,029)	(203)
Operating lease liabilities	(621)	(541)
Net cash used in operating activities	(29,823)	(25,846)
Cash flows from investing activities:
Purchases of short-term investments	(84,418)
Maturities of short-term investments		117,030
Purchases of property and equipment	(817)	(2,033)
Net cash (used in) provided by investing activities	(85,235)	114,997
Cash flows from financing activities:
Proceeds from issuance of common stock pursuant to employee stock purchase plan	446	537
Proceeds from issuance of common stock from option exercises	143	135
Payment of deferred offering costs		(225)
Net cash provided by financing activities	2,043	447
Net change in cash, cash equivalents and restricted cash	(113,015)	89,598
Cash, cash equivalents and restricted cash, beginning of period	218,705	55,048
Cash, cash equivalents and restricted cash, end of period	105,690	144,646
Supplemental disclosures of noncash investing and financing activities:
Reclassification of liability for common stock vested	4	12
Property and equipment additions included in accounts payable	367	405
Property and equipment additions included in accrued expenses and other liabilities	164	23
Unrealized loss on available for sale securities, net	(23)	(202)
Deferred offering costs included in accounts payable and accrued expenses		$ 77
ATM
Cash flows from financing activities:
Proceeds from issuance of common stock pursuant to ATM, net of discounts and issuance costs	$ 1,454