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Debt (Summary of Debt) (Details) - USD ($)	12 Months Ended
Debt (Summary of Debt) (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019	Dec. 21, 2016
Debt [Line Items]
Short-term debt	$ 29,145,000	$ 4,705,000
Less: unamortized debt issue costs	(2,953,000)
Total long-term debt	636,648,000	645,481,000
Total debt	665,793,000	650,186,000
Current portion	10,360,000	18,277,000
Non-current portion	626,288,000	627,204,000
Term Loan and Long-term Revolver Loan [Member]
Debt [Line Items]
Less: unamortized debt issue costs	(690,000)	(807,000)
Senior Unsecured Notes [Member]
Debt [Line Items]
Less: unamortized debt issue costs	(7,266,000)	(9,067,000)
2.72% Term Loan, Due October 2021 [Member] \| Term Loan and Long-term Revolver Loan [Member]
Debt [Line Items]
Long-term Debt	98,420,000	155,355,000
2.72% Long-term Revolver Loan, Due October 2021 [Member] \| Term Loan and Long-term Revolver Loan [Member]
Debt [Line Items]
Long-term Debt	$ 46,184,000
Delayed Draw Term Loan, In Canadian Dollars, Available until October 2021 [Member] \| Term Loan and Long-term Revolver Loan [Member]
Debt [Line Items]
Weighted average interest rate	2.72%
Maturity date	Oct. 01, 2023
Delayed Draw Term Loan, In US Dollars, Available until October 2021 [Member] \| Term Loan and Long-term Revolver Loan [Member]
Debt [Line Items]
Weighted average interest rate	2.72%
Maturity date	Oct. 01, 2021
5.375% Senior Unsecured Note, Due January 2025 [Member] \| Senior Unsecured Notes [Member]
Debt [Line Items]
Long-term Debt	$ 500,000,000	$ 500,000,000
Interest rate	5.375%		5.375%
Maturity date	Jan. 01, 2025