Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Operating activities:
Net loss	$ (6,966)	$ (6,096)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	11	10
Stock-based compensation	427	370
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(930)	(149)
Accounts payable and accrued expenses	(486)	(253)
Net cash used in operating activities	(7,944)	(6,118)
Investing activities:
Purchase of short-term investments	(15,604)
Sale of short-term investments	4,202
Purchase of property and equipment		(15)
Net cash used in investing activities	(11,402)	(15)
Financing activities:
Proceeds from issuance of common stock, net of issuance costs		9,195
Net cash provided by financing activities		9,195
(Decrease) increase in cash and cash equivalents	(19,346)	3,062
Cash and cash equivalents at beginning of period	27,285	30,031
Cash and cash equivalents at end of period	$ 7,939	$ 33,093