Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (13,032)	$ (11,525)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	1,699	1,499
Depreciation and amortization	62	29
Other	(26)	41
Changes in operating assets and liabilities:
Prepaid expenses and other assets	(1,003)	(795)
Accrued, other and operating lease liabilities	(2,599)	(1,261)
Accounts payable	(667)	(597)
Net cash used in operating activities	(15,566)	(12,609)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchase of property and equipment	(14)
Net cash used in investing activities	(14)
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	101
Net cash provided by financing activities	445	46,097
Effect of foreign exchange rate changes on cash, cash equivalents and restricted cash	(3)	(20)
NET INCREASE / (DECREASE) IN CASH, CASH EQUIVALENTS AND RESTRICTED CASH	(15,138)	33,468
CASH, CASH EQUIVALENTS AND RESTRICTED CASH - Beginning of period	106,346	100,536
CASH, CASH EQUIVALENTS AND RESTRICTED CASH - End of period	91,208	134,004
SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION:
Cash paid for (refund of) income taxes, net	(29)	73
Cash paid for interest	81
SUPPLEMENTAL DISCLOSURES OF NON-CASH INVESTING AND FINANCING INFORMATION:
Right-of-use asset obtained in exchange for operating lease obligation	$ 771
Property and equipment purchases included in accrued and other liabilities		21
Offering costs included in accrued and other liabilities		$ 209