Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Taxes
Earnings before income tax	$ 190,763	$ 152,512	$ 77,394
Statutory federal and provincial tax rate in Canada	27.00%	27.00%	26.00%
Expected income tax expense	$ 51,506	$ 41,178	$ 20,122
Non-deductible expenses	3,705	4,810	5,668
Adjustments to prior years provision to statutory tax returns	4	1,323	(528)
Changes in the valuation of deferred tax assets	(550)	(771)	(1,089)
Different tax rates of subsidiaries operating in foreign jurisdictions	(11,818)	(17,145)	(12,269)
U.S. tax reform impacts	6,949	4,899	(9,734)
Change in enacted tax rates	(1,016)	93	(229)
Change in estimate of deductibility of stock options			(1,557)
Unrecognized tax benefits	(2,347)	(1,800)	3,291
Benefits of deductible stock options vested and exercised	(1,780)	(2,434)	(1,359)
Other	(3,030)	853	(228)
Income Tax Expense (Benefit), Total	$ 41,623	$ 31,006	$ 2,088