CONDENSED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating activities
Net loss	$ (78,344)	$ (47,329)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation expense	787	960
Amortization of deferred financing costs	316	282
Amortization of deferred compensation for services	145	158
Amortization of (discount) premium on investment securities	274	(227)
Non-cash lease expense	1,318	1,025
Stock-based compensation	6,306	5,622
Change in derivative liabilities	(713)	152
Non-cash interest associated with debt discount accretion	141	257
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(7,379)	(2,144)
Accounts payable	(3,039)	2,025
Accrued compensation and benefits	267	(1,372)
Operating lease liabilities	(1,361)	(1,251)
Accrued and other liabilities	2,607	174
Deferred revenue	182	(2,300)
Net cash used in operating activities	(78,493)	(43,968)
Investing activities
Proceeds from maturities and redemptions of investments	60,550	25,519
Purchases of investments	(48,314)	(62,960)
Purchases of property and equipment	(1,517)	(25)
Net cash provided by (used in) investing activities	10,719	(37,466)
Financing activities
Proceeds from issuance of common stock in at-the-market offering, net of issuance costs	62,446	0
Proceeds from issuance of common stock under equity incentive and stock purchase plans	1,041	795
Net cash provided by financing activities	63,487	795
Net decrease in cash and cash equivalents	(4,287)	(80,639)
Cash and cash equivalents at beginning of period	91,032	181,133
Cash and cash equivalents at end of period	86,745	100,494
Supplementary disclosure of cash flow information:
Cash paid for interest	1,936	2,146
Cash paid for income taxes	3	0
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	$ 0	$ 311