CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities
Net loss	$ (5,999)	$ (5,438)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	31	9
Stock-based compensation expense	1,127	747
Amortization of debt issuance costs		2
Amortization of discount on investments	(25)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(720)	(716)
Accounts payable and accrued expenses	(563)	(1,453)
Net cash used in operating activities	(6,149)	(6,849)
Cash flows from investing activities
Maturities of short-term investments		1,738
Purchases of property and equipment	(8)	(126)
Net cash (used in) provided by investing activities	(8)	1,612
Cash flows from financing activities
Principal payments of notes payable		(875)
Proceeds from equity offerings, net of offering costs		2,510
Repayments of short-term bank borrowings	(193)
Net cash (used in) provided by financing activities	(193)	1,635
Net decrease in cash and cash equivalents	(6,350)	(3,602)
Cash and cash equivalents—beginning of period	33,531	26,178
Cash and cash equivalents—end of period	$ 27,181	22,576
Supplemental disclosure of cash flow information
Cash paid for interest		87
Property and equipment in accounts payable		17
Accrued equity offering costs		$ 50