STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Cash flows from operating activities
Net loss	$ (9,990)	$ (16,165)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	22	9
Stock-based compensation expense	1,519	1,476
Amortization of debt issuance costs	4	4
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(484)	1,186
Accounts payable and accrued expenses	(2,284)	1,228
Net cash used in operating activities	(11,213)	(12,262)
Cash flows from investing activities
Purchases of investments		(2,434)
Maturities of short-term investments	3,178	2,735
Purchases of property and equipment	(143)	(406)
Net cash provided by (used in) investing activities	3,035	(105)
Cash flows from financing activities
Proceeds from exercise of stock options		123
Proceeds from equity offerings, net of offering costs	3,281	(167)
Principal payments of notes payable	(1,750)	(209)
Net cash provided by (used in) financing activities	1,531	(253)
Net decrease in cash and cash equivalents	(6,647)	(12,620)
Cash and cash equivalents-beginning of period	26,178	51,722
Cash and cash equivalents-end of period	19,531	39,102
Supplemental disclosure of cash flow information
Cash paid for interest	$ 162	243
Payment on notes payable in accounts payable		43
Property and equipment in accounts payable		$ 227