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Debt (Summary of Debt) (Details) - USD ($) $ in Thousands	9 Months Ended
Debt (Summary of Debt) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Dec. 21, 2016
Debt [Line Items]
Short-term debt	$ 18,481	$ 29,145
Total long-term debt	633,692	636,648
Total debt	652,173	665,793
Current portion	1,172	10,360
Non-current portion	632,520	626,288
Term Loan and Long-term Revolver Loan [Member]
Debt [Line Items]
Less: unamortized debt issue costs	(590)	(690)
Senior Unsecured Notes [Member]
Debt [Line Items]
Less: unamortized debt issue costs	(5,922)	(7,266)
Revolver Loan [Member]
Debt [Line Items]
Long-term Debt	$ 46,442	46,184
Weighted average interest rate	2.61%
2.61% Term Loan, Due September 2026 [Member] \| Term Loan and Long-term Revolver Loan [Member]
Debt [Line Items]
Long-term Debt	$ 93,762	98,420
Delayed Draw Term Loan, In Canadian Dollars, Available until September 2026 [Member] \| Term Loan and Long-term Revolver Loan [Member]
Debt [Line Items]
Weighted average interest rate	2.61%
5.375% Senior Unsecured Note, Due January 2025 [Member] \| Senior Unsecured Notes [Member]
Debt [Line Items]
Long-term Debt	$ 500,000	$ 500,000
Interest rate	5.375%		5.375%
Maturity date	Jan. 15, 2025