Income Taxes - Components of Deferred Income Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets, Net [Abstract]
Canadian net operating losses	$ 35,605	$ 24,049
U.S. net operating losses	3,749	3,889
Research and development deductions and credits	8,234	7,331
Other	1,810	1,389
Less: valuation allowance	(49,398)	(36,658)
Net deferred income tax assets	$ 0	$ 0