Income Taxes - Statutory and Effective Tax Rates Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Canadian statutory tax rates	26.00%	26.00%	26.00%
Loss before income taxes	$ (126,127)	$ (52,405)	$ (22,987)
Expected income tax benefit	32,793	13,625	5,977
Net increase in valuation allowance	(13,895)	(13,684)	(2,486)
Investment tax credits	(172)	868	(222)
Stock-based compensation	(270)	(133)	(606)
Foreign rate differential	1,198	532	0
U.S. and Canada rate change	(19,774)	0	0
Non-taxable expenditures	0	0	76
Change in uncertain tax positions	(20)	0	(1,784)
Adjustments to capital losses for settlement of uncertain tax positions	0	0	(560)
Other	(443)	(1,673)	(417)
(Provision) for income taxes	$ (583)	$ (465)	$ (22)