Condensed Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Cash flows from operating activities:
Net loss	$ (26,633)	$ (24,722)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	372	436
Stock-based compensation	3,688	3,774
Amortization of premiums on short-term investments	0	49
Amortization of debt discount	87	88
Impairment of property, plant and equipment	0	727
Changes in operating assets and liabilities:
Prepaid and other assets	(144)	(194)
Accounts payable	1,137	448
Accrued expenses	(1,326)	(879)
Accrued compensation	(1,018)	(1,587)
Right-of-use assets and lease liabilities, net	(154)	(90)
Net cash used in operating activities	(23,991)	(21,950)
Cash flows from investing activities:
Maturities of short-term investments	0	42,745
Purchases of property and equipment	(388)	(243)
Proceeds from disposition of business	0	768
Net cash (used in) provided by investing activities	(388)	43,270
Cash flows from financing activities:
Proceeds from issuance of common stock and pre-funded warrants, net of issuance costs	0	32,207
Proceeds from issuance of long-term debt, net of issuance costs	0	674
Proceeds from exercise of stock options	41	6
Proceeds from issuance of common stock under employee stock purchase plan	74	122
Net cash provided by financing activities	115	33,009
Net change in cash, cash equivalents and restricted cash	(24,264)	54,329
Cash, cash equivalents and restricted cash at beginning of period	78,114	31,469
Cash, cash equivalents and restricted cash at end of period	53,850	85,798
Cash and cash equivalents at end of period	53,148	85,096
Restricted cash at end of period	702	702
Cash, cash equivalents and restricted cash at end of period	53,850	85,798
Supplemental cash flow disclosures
Cash paid for interest	724	686
Supplemental disclosure of non-cash investing activities:
Purchase of property and equipment in accounts payable and accrued expenses	$ 111	$ 29