Income Taxes (Summary of Income Tax Expense (Recovery)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes [Abstract]
Canadian, Current tax expense	$ 13,209	$ 14,245	$ 30,525
Canadian, Deferred tax expense (recovery)	3,958	(10,192)	(2,068)
Current tax expense before application of operating loss carryforwards	19,851	8,987	12,126
Tax benefit of operating loss carryforwards	(8,293)	(3,876)	(2,310)
Total foreign current tax expense	11,558	5,111	9,816
Deferred tax expense before adjustment to opening valuation allowance	2,386	(6,317)	(1,291)
Adjustment to opening valuation allowance	(105)	(759)
Total foreign deferred tax expense	2,281	(7,076)	(1,291)
Income tax expense	$ 31,006	$ 2,088	$ 36,982