Income Taxes (Summary of Income Tax Expense (Recovery)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Abstract]
Canadian, Current tax expense	$ 14,245	$ 30,525	$ 27,623
Canadian, Deferred tax expense	(10,192)	(2,068)	1,880
Current tax expense before application of operating loss carryforwards	8,987	12,126	16,707
Tax benefit of operating loss carryforwards	(3,876)	(2,310)	(1,910)
Total foreign current tax expense	5,111	9,816	14,797
Deferred tax expense before adjustment to opening valuation allowance	(6,317)	(1,291)	(273)
Adjustment to opening valuation allowance	(759)		(6,166)
Total foreign deferred tax expense	(7,076)	(1,291)	(6,439)
Income tax expense	$ 2,088	$ 36,982	$ 37,861