STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities:
Net loss	$ (41,050)	$ (154,073)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	259	227
Stock-based compensation	6,165	6,094
Preferred stock issued in exchange for a license agreement		118,936
Change in fair value of derivative liabilities	1,292	(21)
Issuance of common stock in a license agreement		87
(Increase) decrease in:
Receivables	8	421
Prepaid expenses and other current assets	(6,660)	(9,611)
Other noncurrent assets	(3)	1
Increase (decrease) in:
Accounts payable	1,368	(194)
Accrued expenses	1,002	(1,542)
Deferred revenue	(4,792)	(5,264)
Deferred rent	(102)	(322)
Net cash used in operating activities	(42,513)	(45,261)
Cash flows from investing activities:
Purchases of property and equipment	(461)	(469)
Net cash used in investing activities	(461)	(469)
Cash flows from financing activities:
Proceeds from exercise of stock options	99	551
Repurchase of restricted common stock	(1,042)	(853)
Repurchase of common stock		(2)
Proceeds from issuance of common stock, net of commissions and expenses of $2.7 million	47,270
Net cash provided by (used in) financing activities	46,327	(304)
Net decrease in cash and cash equivalents	3,353	(46,034)
Cash and cash equivalents, beginning of period	81,053	140,717
Cash and cash equivalents, end of period	84,406	94,683
Supplementary disclosure of cash flow information:
Cash paid for interest	0	0
Cash paid for income taxes	0	0
Series 1 Preferred Stock
Supplementary disclosure of noncash investing and financing activities:
Issuance of stock		119,045
Payment of dividends in preferred stock	$ 13,939	$ 3,591