Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net loss	$ (19,981)	$ (26,669)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation	3,556	4,535
Non-cash discount amortization on term loan	247	58
Change in assets and liabilities:
Prepaid expenses and other assets	(520)	(150)
Accounts payable	(1,674)	2,241
Accrued and other liabilities	574	(156)
Net cash used in operating activities	(17,798)	(20,141)
Financing activities
Proceeds from issuance of term loan		10,000
Issuance costs related to term loan	(10)	(33)
Exercise of stock options	84	41
Exercise of warrants		156
Proceeds from sale of common stock	25,150	12,541
Issuance costs	(2,093)	(1,257)
Net cash provided by financing activities	23,131	21,448
Net increase (decrease) in cash and cash equivalents	5,333	1,307
Cash and cash equivalents at beginning of period	18,473	24,033
Cash and cash equivalents at end of period	23,806	25,340
Supplemental disclosure of cash flow information:
Cash paid for interest	358	46
Supplemental non-cash financing transactions:
Issuance of warrants in connection with term loan	$ 196
Issuance costs related to term loan and offering in accounts payable and accrued liabilities		$ 89