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Debt (Summary of Debt) (Details) - USD ($) $ in Thousands		12 Months Ended
Debt (Summary of Debt) (Details) - USD ($) $ in Thousands	Dec. 21, 2016	Dec. 31, 2017	Dec. 31, 2016
Debt [Line Items]
Short-term debt		$ 7,018	$ 23,912
Long-term Debt, Total		812,892	595,706
Total debt		819,910	619,618
Current portion		16,907
Non-current portion		$ 795,985	595,706
Revolving Loan, In Canadian Dollars, Available until October 2021 [Member]
Debt [Line Items]
Long-term Debt			69,926
Weighted average interest rate		2.38%
Maturity date		Oct. 01, 2021
Revolving Loan, In US Dollars, Available until October 2021 [Member]
Debt [Line Items]
Long-term Debt			30,000
Weighted average interest rate		2.075%
Maturity date		Oct. 01, 2021
Delayed Draw Term Loan, In Canadian Dollars, Available until October 2021 [Member]
Debt [Line Items]
Long-term Debt		$ 185,143
Weighted average interest rate		3.69%
Maturity date		Oct. 01, 2021
Delayed Draw Term Loan, In US Dollars, Available until October 2021 [Member]
Debt [Line Items]
Long-term Debt		$ 144,544
Less: unamortized debt issue costs		$ (4,134)
Weighted average interest rate		3.662%
Maturity date		Oct. 01, 2021
5.375% Senior Unsecured Note, Due January 2025 [Member]
Debt [Line Items]
Long-term Debt		$ 500,000	500,000
Less: unamortized debt issue costs	$ (13,945)	$ (12,661)	$ (4,220)
Interest rate	5.375%	5.375%
Maturity date	Jan. 15, 2025