Statements of Cash Flows - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net loss	$ (10,223,000)	$ (8,800,000)
Adjustment to reconcile net loss to net cash used in operating activities:
Depreciation and amortization expense	77,000	87,000
Gain on disposal of property and equipment		(10,000)
Non-cash share-based compensation expense	1,535,000	1,846,000
Fair value of common stock issued in exchange for patent and technology rights	228,000
Changes in operating assets and liabilities:
Prepaid expenses	131,000	(139,000)
Accounts payable	878,000	122,000
Accrued expenses	104,000	(793,000)
Deferred revenue	(47,000)	(71,000)
Net cash used in operating activities	(7,317,000)	(7,758,000)
Cash flows from investing activities:
Purchase of short-term investments	(8,000,000)	(5,000,000)
Maturities of short-term investments	2,500,000	8,000,000
Cash paid for purchase of property and equipment	(57,000)	(95,000)
Proceeds from disposal of property and equipment		12,000
Net cash (used in) provided by investing activities	(5,557,000)	2,917,000
Cash flows from financing activities:
Net proceeds from the issuance of common stock	9,266,000	1,886,000
Proceeds from the issuance of common stock upon the exercise of warrants	198,000
Proceeds from the issuance of common stock in connection with the employee stock purchase plan	31,000	61,000
Net cash provided by financing activities	9,495,000	1,947,000
Net decrease in cash and cash equivalents	(3,379,000)	(2,894,000)
Cash and cash equivalents at the beginning of period	8,496,000	11,390,000
Cash and cash equivalents at the end of period	5,117,000	8,496,000
Supplemental disclosure of non-cash investing and financing activities:
Exchange of Series A convertible preferred stock into Series A-1 convertible preferred stock	2,000,000	3,000,000
Conversion of Series A and Series A-1 convertible preferred stock into common stock	6,814,000	3,882,000
Fair value of Series A and Series A-1 convertible preferred stock dividends	209,000	4,130,000
Series A and Series A-1 convertible preferred stock dividends	$ 126,000	$ 596,000