Income Taxes - Income Tax (Recovery) Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Computed recoveries at Canadian federal and provincial tax rates	$ (8,000)	$ (5,980)	$ (4,095)
Change in valuation allowance	9,210	6,897	2,482
Investment tax credits earned	(1,393)	(1,500)	(1,220)
Tax attributes expired/utilized	683	617	2,851
Non-deductible expenditures	594	569	977
Financing fees in equity		(531)
Effect of tax rate increases	(1,444)
Other	$ 350	$ (72)	$ (995)