Income Taxes (Schedule of Effective Income Tax Rate Reconciliation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Abstract]
Income before income taxes	$ 77,394	$ 130,494	$ 176,436
Statutory federal and provincial tax rate in Canada	26.00%	26.00%	26.00%
Expected income tax expense	$ 20,122	$ 33,928	$ 45,873
Impairment of Goodwill		6,129
Non-deductible expenses	5,668	3,891	2,579
Non-taxable income	(105)	(624)
Sale of capital property			(1,291)
Changes in the valuation of deferred tax assets	(1,089)	(259)	(5,828)
Different tax rates of subsidiaries operating in foreign jurisdictions	(12,269)	(3,786)	(3,426)
Change in enacted rates	(10,299)	51	307
Change in estimate of deductibility of stock options	(1,557)
Unrecognized tax benefits	3,291	799	1,362
Benefits of deductible stock options vested and exercised	(1,359)	(1,042)	(666)
Deductions for tax purposes in excess of accounting expenses	(380)	(490)	(232)
Other	65	(1,615)	(817)
Income tax expense	$ 2,088	$ 36,982	$ 37,861