Consolidated statements of cash flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Operating activities
Net loss	$ (31,585)	$ (50,183)	$ (37,002)
Non-cash items and reclassifications:
Change in fair value of derivative liability (Note 9)			(81)
Stock-based compensation (Note 7(e))	4,698	3,839	1,966
Unrealized foreign exchange loss and others	741	709	185
Changes in operating assets and liabilities:
Receivable, prepayments and deposits	1,041	(905)	(109)
Accounts payable and other liabilities	(6,472)	1,822	4,815
Cash used in operating activities	(31,577)	(44,718)	(30,226)
Investing activities
Purchase of investments		(5,995)	(106,442)
Proceeds from maturity of investments	56,000	70,500	59,097
Purchase of property and equipment	(49)	(494)	(713)
Cash provided by (used in) investing activities	55,951	64,011	(48,058)
Financing activities
Proceeds from exercise of stock options	602	438	440
Payment on capital lease obligations	(32)	(15)	(4)
Public offering of common stock (Note 7(c))			75,368
Public offering costs (Note 7(c))			(4,692)
Cash provided by financing activities	570	423	71,112
Effect of exchange rate changes on cash and cash equivalents	(48)	15	(53)
Net change in cash and cash equivalents during the year	24,896	19,731	(7,225)
Cash and cash equivalents, beginning of year	52,032	32,301	39,526
Cash and cash equivalents, end of year	76,928	52,032	32,301
Supplemental disclosure of cash flow information:
Interest paid	4	4	1
Interest received	$ 1,684	1,342	695
Non-cash investing and financing activities:
Accrued purchase of property & equipment		(77)	77
Accrued offering costs		$ (30)
Assets acquired through capital leases			65
Exercise of warrants on a net settlement basis			$ 43