STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Cash flows from operating activities
Net loss	$ (14,160)	$ (22,628)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	35	16
Stock-based compensation expense	2,251	2,276
Amortization of debt issuance costs	4	5
Amortization of discount on investments	(3)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(383)	1,054
Accounts payable and accrued expenses	(2,080)	556
Net cash used in operating activities	(14,336)	(18,721)
Cash flows from investing activities
Purchases of investments	(24,892)	(2,434)
Maturities of short-term investments	3,426	4,225
Purchases of property and equipment	(192)	(643)
Net cash (used in) provided by investing activities	(21,658)	1,148
Cash flows from financing activities
Proceeds from exercise of stock options		123
Principal payments of notes payable	(5,247)	(1,210)
Proceeds from equity offerings, net of offering costs	52,593	(167)
Net cash provided by (used in) financing activities	47,346	(1,254)
Net increase (decrease) in cash and cash equivalents	11,352	(18,827)
Cash and cash equivalents-beginning of period	26,178	51,722
Cash and cash equivalents-end of period	37,530	32,895
Supplemental disclosure of cash flow information
Cash paid for interest	184	360
Payment on notes payable in accounts payable		43
Property and equipment in accounts payable		$ 6
Accrued equity offering costs	$ 45