STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities:
Net loss	$ (79,976)	$ (117,796)	$ (53,117)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	1,128	629	575
Stock-based compensation	6,829	7,341	7,534
Non-cash inducement warrant expense		60,751
Change in fair value of derivative liabilities	0	0	(158)
(Increase) decrease in:
Receivables	(1,335)	(1,466)	(1,845)
Prepaid expenses and other current assets	11,566	(1,729)	(1,263)
Right of use assets	(2,378)
Deposits		(2)
Other noncurrent assets	(635)	9,431	3,942
Increase (decrease) in:
Accounts payable	54	199	(3,709)
Accrued expenses	5,272	1,725	(1,145)
Deferred revenue			(146)
Deferred rent			(125)
Lease liabilities	2,462	63
Net cash used in operating activities	(57,013)	(40,854)	(49,457)
Cash flows from investing activities:
Purchases of property and equipment	(9,778)	(284)	(459)
Net cash used in investing activities	(9,778)	(284)	(459)
Cash flows from financing activities:
Proceeds from exercise of stock options	442	1,219	240
Repurchase of common stock		(653)	(1,622)
Proceeds from underwritten financing			47,101
Issuance of common stock upon exercise of warrants, net		52,499
Issuance of common stock in connection with a public offering, net	88,661
Issuance of common stock in connection with an at the market offering, net	13,016	6,085
Cash paid for settlement of related party relationship			(5,408)
Net cash provided by financing activities	102,119	59,150	40,311
Net decrease in cash and cash equivalents, and restricted cash	35,328	18,012	(9,605)
Cash and cash equivalents, and restricted cash, beginning of period	79,741	61,729	71,334
Cash and cash equivalents, and restricted cash, end of period	115,069	79,741	61,729
Supplementary disclosure of cash flow information:
Bonus paid in common stock		1,000
Fixed assets in accrued expenses	$ 471	$ 358
Supplementary disclosure of noncash investing and financing activities:
Noncash portion of related party relationship settlement			212,769
Series 1 Preferred Stock
Supplementary disclosure of noncash investing and financing activities:
Payment of dividends in preferred stock			$ 16,998