Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Operating activities
Net loss	$ (15,470)	$ (24,413)
Reconciliation of net loss to net cash used in operating activities:
Depreciation	83	115
Amortization of premium/discount on available-for-sale securities	(35)	(2)
Foreign currency remeasurement (loss)/gain	(25)	196
Stock-based compensation	2,647	2,459
Changes in:
Prepaid expenses and other assets	589	1,049
Interest receivable	(3)	(73)
Accounts payable and accrued expenses	(6,706)	4,015
Net cash used in operating activities	(18,920)	(16,654)
Investing activities
Purchases of available-for-sale investments	(12,951)	(31,443)
Proceeds from maturities of available-for-sale investments	23,990	8,920
Proceeds from sale of available-for-sale investments	1,999
Purchase of property and equipment	(24)	(23)
Net cash provided by (used in) investing activities	13,014	(22,546)
Financing activities
Proceeds from issuance of common stock, net of issuance costs	2,853	1,287
Proceeds from the issuance of Series A Convertible Preferred Stock, net of issuance costs		21,536
Proceeds from issuance of common stock under ESPP	84	58
Exercise of stock options		109
Net cash provided by financing activities	2,937	22,990
Effect of exchange rate changes on cash	24	(196)
Decrease in cash, cash equivalents and restricted cash	(2,945)	(16,406)
Cash, cash equivalents and restricted cash, beginning of period	21,192	36,414
Cash, cash equivalents and restricted cash, end of period	$ 18,247	$ 20,008