Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Condensed Statements of Cash Flows
Net loss	$ (7,224)	$ (7,496)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	1,020	836
Non-cash discount amortization on term loan and convertible notes	77
Change in assets and liabilities:
Prepaid expenses and other assets	168	161
Accounts payable	(1,304)	1,473
Accrued and other liabilities	27	(1,197)
Net cash used in operating activities	(7,236)	(6,223)
Net cash used in operating activities	(7,236)	(6,223)
Financing activities
Exercise of stock options	23	3
Proceeds from sale of common stock	25,150	12,541
Offering costs	(1,949)	(1,072)
Net cash provided by financing activities	23,224	11,472
Net increase in cash and cash equivalents	15,988	5,249
Cash and cash equivalents at beginning of period	18,473	24,033
Cash and cash equivalents at end of period	34,461	29,282
Supplemental disclosure of cash flow information:
Cash paid for interest	112
Supplemental non-cash financing transactions:
Offering costs in accounts payable and accrued liabilities	$ 144	$ 147