Debt (Summary of Debt) (Details) - USD ($) $ in Thousands	9 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Debt [Line Items]
Short-term debt	$ 10,532	$ 7,018
Long-term Debt, Total	751,778	812,892
Total debt	762,310	819,910
Current portion	11,556	16,907
Non-current portion	740,222	795,985
Delayed Draw Term Loans [Member]
Debt [Line Items]
Less: unamortized debt issue costs	(2,940)	(4,134)
Senior Unsecured Notes [Member]
Debt [Line Items]
Less: unamortized debt issue costs	(11,317)	(12,661)
Delayed Draw Term Loan, In Canadian Dollars, Available until October 2021 [Member] \| Delayed Draw Term Loans [Member]
Debt [Line Items]
Long-term Debt	$ 173,345	$ 185,143
Weighted average interest rate	4.015%	4.015%
Maturity date	Oct. 01, 2021
Delayed Draw Term Loan, In US Dollars, Available until October 2021 [Member] \| Delayed Draw Term Loans [Member]
Debt [Line Items]
Long-term Debt	$ 92,690	$ 144,544
Weighted average interest rate	4.219%	4.219%
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	$ 500,000
Interest rate	5.375%	5.375%
Maturity date	Jan. 01, 2025

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format.

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Represents the aggregate of total long-term debt, including current maturities and short-term debt.

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Weighted average interest rate of debt outstanding.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt, classified as current. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

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