Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating activities
Net loss	$ (14,131)	$ (14,850)
Reconciliation of net loss to net cash used in operating activities:
Depreciation and amortization	105	165
Stock-based compensation expense	924	986
Accretion of discount/premium on investment securities		25
Non-cash interest expense	33	94
Gain on disposal of property and equipment	(148)	(30)
Services received in non-monetary exchange	5
Changes in assets and liabilities:
Prepaid expenses and other current assets	641	109
Accounts payable	(402)	650
Accrued expenses	547	(952)
Deferred rent	5	18
Net cash used in operating activities	(12,421)	(13,785)
Investing activities
Sales and maturities of available-for-sale securities		14,910
Purchases of property and equipment		(39)
Proceeds from sale of property and equipment	8	30
Net cash provided by investing activities	8	14,901
Financing activities
Proceeds from initial public offering, net of issuance costs	39,325
Proceeds from at-the-market offering, net of issuance costs	8,313	6,301
Proceeds from exercise of common stock options and warrants	4	23
Payments on borrowing	(1,667)	(1,667)
Net cash provided by financing activities	45,975	4,657
Net increase in cash, cash equivalents and restricted cash	33,562	5,773
Cash, cash equivalents and restricted cash, beginning of period	16,482	23,709
Cash, cash equivalents and restricted cash, end of period	50,044	29,482
Supplemental disclosure of cash flow information
Cash paid for interest	68	$ 195
Non-cash financing activities
Public offering issuance costs in current liabilities	$ 414