Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (27,910)	$ (23,485)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	3,457	3,281
Depreciation and amortization	126	59
Other	(4)	(170)
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,071)	(1,043)
Accrued, other and operating lease liabilities	(2,136)	693
Accounts payable	(84)	(212)
Net cash used in operating activities	(27,622)	(20,877)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(19)	(30)
Net cash used in investing activities	(19)	(30)
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock upon follow-on offering, net of offering costs		45,996
Proceeds from exercise of common stock options	445	133
Net cash provided by financing activities	445	46,129
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash	(19)	(33)
NET INCREASE / (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(27,215)	25,189
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — Beginning of period	106,346	100,536
CASH, CASH EQUIVALENTS AND RESTRICTED CASH — End of period	79,131	125,725
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for (refund of) income taxes, net	(21)	$ 104
Cash paid for interest	163
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Right-of-use asset obtained in exchange for operating lease obligation	$ 771