Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net loss	$ (30,704)	$ (22,997)	$ (15,752)
Items not involving cash:
Depreciation	649	864	1,038
Amortization of discount on term loan	11
Stock-based compensation	2,236	2,161	3,729
Unrealized foreign exchange (gain) loss	(1,474)	(1,300)	6,902
Changes in operating assets and liabilities:
Accounts receivable	(232)	121	(107)
Prepaid expenses, and other current assets	613	571	(1,214)
Prepaid expenses, long term	178	686	(1,094)
Accounts payable and accrued expenses	(3)	484	17
Deferred revenue		(157)	(11,622)
Net cash used in operating activities	(28,726)	(19,567)	(18,103)
Investing activities:
Purchases of property, plant and equipment	(315)	(279)	(551)
Purchase of marketable securities	(28,007)	(47,563)
Proceeds from marketable securities	52,616		10,745
Net cash provided by (used in) investing activities	24,294	(47,842)	10,194
Financing activities:
Proceeds from issuance of term loan, net of issuance costs (note 8)	6,893
Issuance of common shares pursuant to exercise of stock options	177	132	278
Issuance of common shares, net of issuance costs (note 9a)		23,832
Net cash provided by financing activities	7,070	23,964	278
Effect of exchange rate changes on cash and cash equivalents	753	1,889	(5,744)
Increase (decrease) in cash and cash equivalents	3,391	(41,556)	(13,375)
Cash and cash equivalents, beginning of year	17,095	58,651	72,026
Cash and cash equivalents, end of year	20,486	17,095	58,651
Supplemental disclosures:
Interest received	740	341	659
Supplemental disclosures of non-cash transactions:
Fair value of options exercised on a cashless basis	$ 25	$ 404	$ 744