Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Cash flow from operating activities:
Net loss	$ (12,673)	$ (36,621)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,664	1,423
Share-based compensation	2,204	3,758
Loss on disposal and write-offs of property and equipment	154	45
Change in fair value of warrant liability	(16,566)	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(224)	75
Accounts payable	777	(2,523)
Accrued compensation	(701)	(137)
Accrued outside research and development services	(829)	(4,345)
Accrued legal and professional fees	132	(3)
Other accrued expenses	(615)	86
Deferred revenue	(1,610)	8,577
Other long-term assets	(338)	(192)
Net cash used in operating activities	(28,625)	(29,857)
Cash flow from investing activities:
Purchases of property and equipment	(1,107)	(2,168)
Proceeds from the sale of property and equipment	49	26
Net cash used in investing activities	(1,058)	(2,142)
Cash flow from financing activities:
Proceeds from public offering, net of underwriting fees and commissions	35,625	0
Payments related to public offering costs	(321)	(159)
Proceeds from exercise of stock options	60	81
Payments on capital lease obligation	(11)	(10)
Net cash provided by (used in) financing activities	35,353	(88)
Net increase (decrease) in cash, cash equivalents and restricted cash	5,670	(32,087)
Cash, cash equivalents and restricted cash as of beginning of period	3,063	35,150
Cash, cash equivalents and restricted cash as of end of period	8,733	3,063
Supplemental disclosure of cash flow information:
Cash paid for interest	1,043	1,011
Supplemental disclosure of non-cash investing and financing activities:
Purchases of property and equipment with accounts payable and accrued expenses	0	80
Non-cash addition to deferred offering costs	0	138
Deferred offering costs reclassified to additional paid-in capital	431	0
Reconciliation to consolidated balance sheets:
Cash, cash equivalents and restricted cash as of end of period	$ 3,063	$ 35,150