Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Cash flows from operating activities:
Net loss	$ (72,769)	$ (52,106)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,361	1,896
Stock-based compensation expense	15,458	8,194
Amortization of premium/(discount) and accrued interest on marketable securities	1,398	(429)
Other	(81)	(6)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,653)	7,298
Other assets	(99)	(8)
Operating lease right-of-use asset	1,505	952
Accounts payable	(394)	6,962
Accrued expenses and other current liabilities	(583)	(2,507)
Lease liability	(1,363)	(769)
Net cash used in operating activities	(56,220)	(30,523)
Cash flows from investing activities:
Purchases of marketable securities	(199,959)	(319,690)
Maturities of marketable securities	240,377	160,900
Sales of marketable securities	8,990	6,748
Purchases of property and equipment	(5,052)	(7,328)
Net cash provided by (used in) investing activities	44,356	(159,370)
Cash flows from financing activities:
Proceeds from offerings of common stock, net of issuance costs	1,685	140,822
Proceeds from issuance of common stock pursuant to option exercises	51	12,101
Taxes paid related to net share settlement of restricted stock units	0	(2,043)
Proceeds from employee stock purchase plan	526	475
Repayment of loan	(240)	0
Net cash provided by financing activities	2,022	151,355
Net decrease in cash and cash equivalents and restricted cash	(9,842)	(38,538)
Cash and cash equivalents and restricted cash at beginning of period	63,423	66,896
Cash and cash equivalents and restricted cash at end of period	53,581	28,358
Cash and cash equivalents	47,299	27,359
Restricted cash	6,282	999
Cash and cash equivalents and restricted cash at end of period	53,581	28,358
Supplemental schedule of noncash investing and financing information
Right-of-use assets obtained in exchange for lease liability	84,005	0
Fixed assets in accounts payable, accrued expenses and other current liabilities	$ 1,562	$ 2,391