Income Taxes (Summary of Income Tax Expense (Recovery)) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income taxes
Canadian, Current tax expense	$ 27,766	$ 19,752	$ 13,209
Canadian, Deferred tax expense (recovery)	3,970	3,346	3,958
Current tax expense before application of operating loss carryforwards	30,280	24,815	19,851
Tax benefit of operating loss carryforwards	(1,668)	(11,770)	(8,293)
Total foreign current tax expense	28,612	13,045	11,558
Deferred tax expense before adjustment to opening valuation allowance	6,127	5,727	2,386
Adjustment to opening valuation allowance	(945)	(247)	(105)
Total foreign deferred tax expense (recovery)	5,182	5,480	2,281
Income tax expense	$ 65,530	$ 41,623	$ 31,006