CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating activities
Net loss	$ (121,931)	$ (65,437)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	1,247	1,399
Amortization of deferred financing costs	477	416
Amortization of deferred compensation for services	192	235
Amortization of (discount) premium on investment securities	396	(241)
Non-cash lease expense	2,257	1,568
Stock-based compensation	8,568	8,149
Change in derivative liabilities	(696)	290
Non-cash interest associated with debt discount accretion	212	393
Changes in operating assets and liabilities:
Accounts receivable	(287)	0
Prepaid expenses and other assets	(3,927)	(3,748)
Accounts payable	(1,363)	303
Accrued compensation and benefits	(902)	(731)
Operating lease liabilities	(2,033)	(1,914)
Accrued and other liabilities	5,411	(871)
Deferred revenue	(703)	(3,656)
Net cash used in operating activities	(113,082)	(63,845)
Investing activities
Proceeds from maturities and redemptions of investments	103,550	79,402
Purchases of investments	(72,736)	(107,200)
Purchases of property and equipment	(1,962)	(74)
Net cash provided by (used in) investing activities	28,852	(27,872)
Financing activities
Proceeds from issuance of common stock in at-the-market offering, net of issuance costs	67,189	0
Proceeds from issuance of common stock under equity incentive and stock purchase plans	1,403	1,593
Payments for taxes related to net share settlement of equity awards	(106)	0
Net cash provided by financing activities	68,486	1,593
Net decrease in cash and cash equivalents	(15,744)	(90,124)
Cash and cash equivalents at beginning of period	91,032	181,133
Cash and cash equivalents at end of period	75,288	91,009
Supplementary disclosure of cash flow information:
Cash paid for interest	2,920	3,119
Cash paid for income taxes	4	1
Supplementary disclosure of non-cash activities:
Right-of-use assets obtained in exchange for lease obligations	14,379	0
Issuance of common stock for services	$ 190	$ 310