CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net loss	$ (38,712)	$ (26,614)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	195	94
Stock-based compensation expense	4,438	3,645
Loss on disposal of fixed assets	42
Noncash lease expense	166
Noncash lease liability	(232)
Amortization of discount on investments	(5)	(74)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(98)	(210)
Accounts payable and accrued expenses	1,822	4,475
Net cash used in operating activities	(32,384)	(18,684)
Cash flows from investing activities
Maturities of short-term investments	5,000	5,000
Purchases of short-term investments	(2,725)
Purchases of property and equipment	(358)	(6)
Net cash provided by investing activities	1,917	4,994
Cash flows from financing activities
Proceeds from exercise of stock options	97	14
Financing costs	(198)
Repayments of short-term bank borrowings		(193)
Net cash used in financing activities	(101)	(179)
Net decrease in cash and cash equivalents	(30,568)	(13,869)
Cash and cash equivalents—beginning of period	67,727	33,531
Cash and cash equivalents—end of period	37,159	19,662
Supplemental disclosure of cash flow information
Property and equipment in accounts payable	22	$ 31
Operating lease liability	3,357
Operating right-of-use asset	$ 2,458