STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash flows from operating activities:
Net loss	$ (117,796)	$ (53,117)	$ (54,323)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	629	575	369
Stock-based compensation	7,341	7,534	8,454
Non-cash inducement warrant expense	60,751
Change in fair value of derivative liabilities	0	(158)	1,295
(Increase) decrease in:
Receivables	(1,466)	(1,845)	2
Prepaid expenses and other current assets	(1,729)	(1,263)	3,992
Deposits	(2)
Other noncurrent assets	9,431	3,942	(12,991)
Increase (decrease) in:
Accounts payable	199	(3,709)	4,261
Accrued expenses	1,725	(1,145)	800
Deferred revenue		(146)	(6,389)
Deferred rent	0	(125)	(139)
Lease liabilities	63
Net cash used in operating activities	(40,854)	(49,457)	(54,669)
Cash flows from investing activities:
Purchases of property and equipment	(284)	(459)	(737)
Net cash used in investing activities	(284)	(459)	(737)
Cash flows from financing activities:
Proceeds from exercise of stock options	1,219	240	88
Issuance of restricted common stock			(2,059)
Repurchase of common stock	(653)	(1,622)	0
Proceeds from issuance of common stock, net			47,270
Proceeds from underwritten financing		47,101
Issuance of common stock upon exercise of warrants, net	52,499
Issuance of common stock in connection with an at the market offering, net	6,085
Cash paid for settlement of related party relationship		(5,408)
Net cash provided by financing activities	59,150	40,311	45,299
Net decrease in cash and cash equivalents, and restricted cash	18,012	(9,605)	(10,107)
Cash and cash equivalents, and restricted cash, beginning of period	61,729	71,334	81,441
Cash and cash equivalents, and restricted cash, end of period	79,741	61,729	71,334
Supplementary disclosure of cash flow information:
Bonus paid in common stock	1,000
Fixed assets in accrued expenses	$ 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	$ 18,938