STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities:
Net loss	$ (28,054)	$ (28,051)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	296	255
Stock-based compensation	4,255	5,370
Change in fair value of derivative liabilities		(211)
(Increase) decrease in:
Receivables	404	(645)
Prepaid expenses and other current assets	(144)	7,892
Other noncurrent assets	4,672	(8,447)
Deposits	(2)
Increase (decrease) in:
Accounts payable	234	(3,829)
Accrued expenses	36	(1,245)
Deferred revenue		(146)
Deferred rent	17	(74)
Other liabilities	(33)
Net cash used in operating activities	(18,319)	(29,131)
Cash flows from investing activities:
Purchases of property and equipment	(77)	(376)
Net cash used in investing activities	(77)	(376)
Cash flows from financing activities:
Proceeds from exercise of stock options	600	240
Repurchase of common stock	(370)	(1,275)
Net cash provided by (used in) financing activities	230	(1,035)
Net decrease in cash and cash equivalents, and restricted cash	(18,166)	(30,542)
Cash and cash equivalents, and restricted cash, beginning of period	61,729	71,335
Cash and cash equivalents, and restricted cash, end of period	43,563	40,793
Supplementary disclosure of cash flow information:
Compensation paid in common stock, gross	$ 1,000
Series 1 Preferred Stock
Supplementary disclosure of noncash investing and financing activities:
Payment of dividends in preferred stock		$ 10,582