Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities:
Net loss	$ (41,338)	$ (43,324)
Adjustment to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	343	518
Stock-based compensation expense	4,927	4,322
Change in fair value of preferred stock warrant liability	0	51
Non-cash interest expense	354	429
Gain on sale of property and equipment	0	(18)
Changes in current assets and liabilities:
Prepaid expenses and other assets	(935)	(2,108)
Accounts payable	(810)	2,013
Accrued expenses and other current liabilities	(2,249)	536
Net cash used in operating activities	(39,708)	(37,581)
Cash flows from investing activities:
Purchases of property and equipment	(59)	(102)
Proceeds from the sale of property and equipment	0	19
Purchases of marketable securities	(3,196)	0
Net cash used in investing activities	(3,255)	(83)
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs	64,973	64,532
Payment of success fee obligation	0	(1,220)
Proceeds from exercise of common stock options	0	241
Net cash provided by financing activities	64,973	63,553
Net increase in cash and cash equivalents	22,010	25,889
Cash and cash equivalents, beginning of period	92,053	79,466
Cash and cash equivalents, end of period	114,063	105,355
Supplemental cash flow information:
Cash paid for interest	1,842	2,151
Supplemental disclosure of non-cash investing and financing activities:
Reclassification of warrants to additional paid-in capital	0	476
Conversion of preferred stock to common stock upon closing of the initial public offering	0	197,888
Public offering costs incurred but unpaid at period end	$ 20	$ 0