CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities
Net loss	$ (26,614)	$ (14,160)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	94	35
Stock-based compensation expense	3,645	2,251
Amortization of debt issuance costs		4
Amortization of discount on investments	(74)	(3)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(210)	(383)
Accounts payable and accrued expenses	4,475	(2,080)
Net cash used in operating activities	(18,684)	(14,336)
Cash flows from investing activities
Purchases of investments		(24,892)
Maturities of short-term investments	5,000	3,426
Purchases of property and equipment	(6)	(192)
Net cash provided by (used in) investing activities	4,994	(21,658)
Cash flows from financing activities
Proceeds from exercise of stock options	14
Principal payments of notes payable		(5,247)
Proceeds from equity offerings, net of offering costs		52,593
Repayments of short-term bank borrowings	(193)
Net cash (used in) provided by financing activities	(179)	47,346
Net (decrease) increase in cash and cash equivalents	(13,869)	11,352
Cash and cash equivalents—beginning of period	33,531	26,178
Cash and cash equivalents—end of period	19,662	37,530
Supplemental disclosure of cash flow information
Cash paid for interest		184
Accrued equity offering costs		$ 45
Property and equipment in accounts payable	$ 31