Consolidated Statements of Cash Flows (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating activities
Net loss	$ (3,342,000)	$ (7,912,000)	$ (7,970,000)
Reconciliation of net loss to net cash used in operating activities:
Depreciation	30,000	27,000	57,000
Amortization of premium/discount on available-for-sale securities	30,000	30,000	138,000
Gain on sale of fixed assets		(65,000)	(5,000)
Accretion of discount & debt issuance cost of convertible notes payable	742,000	749,000
Stock-based compensation	459,000	155,000	110,000
Change in fair value of investor rights/obligation	(5,151,000)
Change in fair value of derivative liability	81,000	(2,000)
Changes in:
Prepaid expenses and other assets	(961,000)	72,000	348,000
Accounts payable and accrued expenses	955,000	177,000	(912,000)
Accrued interest payable	115,000	112,000
Deferred revenue from sale of option to acquire company	(2,948,000)
Net cash used in operating activities	(9,990,000)	(6,657,000)	(8,234,000)
Investing activities
Purchases of available-for-sale investments	(34,950,000)	(3,878,000)	(8,658,000)
Proceeds from maturities of available for sale investments	22,518,000	6,550,000	16,075,000
Purchase of property and equipment	(51,000)	(10,000)	(67,000)
Sale of property and equipment		65,000	33,000
Deposits			(1,000)
Net cash (used in) provided by investing activities	(12,483,000)	2,727,000	7,382,000
Financing activities
Proceeds from issuance of Series D preferred stock	25,000,000
Issuance costs for preferred stock	(452,000)
Net proceeds from IPO	62,485,000
Proceeds from issuance of convertible notes payable		4,339,000
Payments for debt issuance costs		(46,000)
Exercise of stock options	59,000	21,000
Exercise of warrants	1,428,000
Repayments of debt			(9,000)
Net cash provided by (used in) financing activities	88,520,000	4,314,000	(9,000)
Increase (decrease) in cash and cash equivalents	66,047,000	384,000	(861,000)
Cash and cash equivalents, beginning of period	2,793,000	2,409,000	3,270,000
Cash and cash equivalents, end of period	68,840,000	2,793,000	2,409,000
Supplemental disclosure of non-cash investing and financing activities
Accretion of redeemable convertible preferred stock to redemption value	6,353,000	6,119,000	6,133,000
Fair value of derivative embedded within convertible notes payable		1,445,000
Conversion of convertible notes and accrued interest into Series D Preferred Stock	6,089,000
Conversion of redeemable convertible preferred stock into common stock	126,836,000
Fair value of investors' rights/ obligations reclassified to equity upon IPO	$ 1,408,000