CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities
Net loss	$ (70,471)	$ (50,006)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	262	243
Amortization of debt issuance costs	319
Stock-based compensation expense	10,867	5,521
Noncash contract asset	(41)
Noncash lease expense	232	194
Noncash lease liability	237	276
Changes in operating assets and liabilities:
Refund Liability	21,828
Contract asset	(1,018)
Prepaid expenses and other current assets, non-current assets, and accounts receivable	(453)	(1,496)
Accounts payable, accrued expenses and other long term-liabilities	4,511	754
Net cash used in operating activities	(33,727)	(44,514)
Cash flows from investing activities
Maturities of short-term investments	1,474	5,711
Purchases of short-term investments		(8,931)
Deposit on property and equipment	(1,329)
Purchases of property and equipment	(839)
Net cash used in investing activities	(694)	(3,220)
Cash flows from financing activities
Proceeds from exercise of stock options	902	616
Proceeds from notes payable, net of issuance costs	40,259
Financing costs, paid	(148)
Proceeds from equity offerings, net of offering costs		43,512
Net cash provided by financing activities	41,013	44,128
Net increase (decrease) in cash and cash equivalents	6,592	(3,606)
Cash and cash equivalents-beginning of period	138,509	90,943
Cash and cash equivalents-end of period	145,101	87,337
Supplemental disclosure of cash flow information
Contractual exit fee included in notes payable	900
Property and equipment in accrued expenses	$ 107
Conversion of preferred stock to common stock		$ 17