STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Cash flows from operating activities
Net loss	$ (5,438)	$ (7,216)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	9	2
Stock-based compensation expense	747	739
Amortization of debt issuance costs	2	2
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(716)	1,055
Accounts payable and accrued expenses	(1,453)	(664)
Net cash used in operating activities	(6,849)	(6,082)
Cash flows from investing activities
Deposit on property and equipment		(30)
Maturities of short-term investments	1,738	1,243
Purchases of property and equipment	(126)	(23)
Net cash provided by investing activities	1,612	1,190
Cash flows from financing activities
Proceeds from exercise of stock options		123
Proceeds from equity offerings, net of offering costs	2,510	(142)
Principal payments of notes payable	(875)	(82)
Net cash provided by (used in) financing activities	1,635	(101)
Net decrease in cash and cash equivalents	(3,602)	(4,993)
Cash and cash equivalents-beginning of period	26,178	51,722
Cash and cash equivalents-end of period	22,576	46,729
Supplemental disclosure of cash flow information
Cash paid for interest	87	120
Payment on notes payable in accounts payable		43
Property and equipment in accounts payable	17	$ 378
Accrued equity offering costs	$ 50