CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Cash flows from operating activities
Net loss	$ (24,906)	$ (15,504)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	112	65
Stock-based compensation expense	3,099	2,475
Loss on disposal of fixed assets	42
Noncash lease expense	107
Noncash lease liability interest	(143)
Amortization of discount on investments		(51)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(1,095)	(60)
Accounts payable and accrued expenses	2,404	1,198
Net cash used in operating activities	(20,380)	(11,877)
Cash flows from investing activities
Maturities of short-term investments	5,000
Purchases of investments	(2,482)
Deposit on property and equipment	(6)
Purchases of property and equipment	(340)	(8)
Net cash provided by (used in) investing activities	2,172	(8)
Cash flows from financing activities
Proceeds from exercise of stock options	65	14
Financing costs	(148)
Repayments of short-term bank borrowings		(193)
Net cash used in financing activities	(83)	(179)
Net decrease in cash and cash equivalents	(18,291)	(12,064)
Cash and cash equivalents—beginning of period	67,727	33,531
Cash and cash equivalents—end of period	49,436	$ 21,467
Supplemental disclosure of cash flow information
Operating lease liability	3,357
Operating right-of-use asset	$ 2,458