STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities:
Net loss	$ (4,338)	$ (3,647)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	7	5
Amortization of other assets	90	57
Amortization of premiums and discounts on marketable securities	55
Share-based compensation	101	155
Change in operating assets and liabilities:
Other current assets	(74)	(277)
Other assets		(7)
Accounts payable	(234)	380
Accrued compensation and employee benefits	(478)	(517)
Accrued expenses and other liabilities	527	(32)
Net cash used in operating activities	(4,344)	(3,883)
Cash flows from investing activities:
Purchases of property and equipment		(1)
Purchases of marketable securities	(1,542)	(5,201)
Proceeds from maturities of marketable securities	4,550
Net cash provided by (used in) investing activities	3,008	(5,202)
Cash flows from financing activities:
Proceeds from the issuance of common stock	210
Common stock offering costs	(105)
Net cash provided by financing activities	105
Net decrease in cash and cash equivalents	(1,231)	(9,085)
Cash and cash equivalents, beginning of period	7,401	38,802
Cash and cash equivalents, end of period	6,170	29,717
Supplemental disclosure of noncash investing and financing transactions:
Vendor finance agreement	256
Proceeds receivable from the issuance of common stock	11
Common stock offering costs accrued but not yet paid	47
Change in unrealized loss on marketable securities	$ 10	6
Payable for purchases of marketable securities		$ 1,009