Consolidated statements of cash flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities
Net loss	$ (50,183)	$ (37,002)	$ (21,860)
Non-cash items and reclassifications:
Change in fair value of derivative liability (Note 8)		(81)	52
Stock-based compensation (Note 7(e))	3,839	1,966	1,506
Unrealized foreign exchange loss and others	709	185	580
Changes in operating assets and liabilities:
Receivable, prepayments and deposits	(905)	(109)	(96)
Accounts payable and other liabilities	1,822	4,815	(450)
Cash used in operating activities	(44,718)	(30,226)	(20,268)
Investing activities
Purchase of investments	(5,995)	(106,442)	(60,703)
Proceeds from maturity of investments	70,500	59,097	13,196
Purchase of property and equipment	(494)	(713)	(26)
Cash provided by (used in) investing activities	64,011	(48,058)	(47,533)
Financing activities
Proceeds from exercise of stock options	438	440	1,120
Payment on capital lease obligations	(15)	(4)
Public offering of common stock (Note 7(c))		75,368	98,038
Public offering costs (Note 7(c))		(4,692)	(6,210)
Cash provided by financing activities	423	71,112	92,948
Effect of exchange rate changes on cash and cash equivalents	15	(53)	(527)
Net change in cash and cash equivalents during the year	19,731	(7,225)	24,620
Cash and cash equivalents, beginning of year	32,301	39,526	14,906
Cash and cash equivalents, end of year	52,032	32,301	39,526
Supplemental disclosure of cash flow information:
Interest paid	4	1
Interest received	1,342	695	325
Non-cash investing and financing activities:
Accrued purchase of property & equipment	(77)	77
Accrued offering costs	$ (30)		35
Assets acquired through capital leases		65	$ 11
Exercise of warrants on a net settlement basis		$ 43