Long-Term Debt (Narrative) (Details)	3 Months Ended
	Mar. 31, 2018 USD ($) swap	Mar. 31, 2017 USD ($)	Aug. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2017 USD ($)	Aug. 31, 2017 USD ($)	Apr. 30, 1998 USD ($)
Debt Instrument [Line Items]
Accrued interest expense	$ 1,300,000				$ 1,000,000
Credit agreement, potential increase to term loan and line of credit	100,000,000
Debt issuance costs						$ 14,300,000
Debt issuance costs capitalized	14,000,000
Unamortized costs	12,000,000
Debt issuance costs expensed	1,376,000	$ 1,440,000
Market value adjustments on interest rate swaps, net of tax	$ 4,137,000	1,530,000
Interest Rate Swap
Debt Instrument [Line Items]
Derivative, number of instruments held | swap	4
Remaining notional balance	$ 1,300,000,000
Derivative, average fixed interest rate	1.31%
Asset for Swaps					12,000,000
Interest Rate Swap | Forecast
Debt Instrument [Line Items]
Remaining notional balance			$ 585,000,000	$ 1,100,000,000
Swap
Debt Instrument [Line Items]
Market value adjustments on interest rate swaps, net of tax	$ 4,100,000	(1,500,000)
Deferred taxes on interest rate swaps	1,400,000	$ 900,000
Revolving line of credit borrowings due August 2022 | Revolving line of credit
Debt Instrument [Line Items]
Multicurrency revolving sub-facility	100,000,000
Revolving line of credit borrowings due August 2022 | Letter of Credit
Debt Instrument [Line Items]
Revolving credit facility, letter of credit sub-facility	$ 50,000,000
Minimum | Interest Rate Swap
Debt Instrument [Line Items]
Derivative, average fixed interest rate	1.03%
Maximum | Interest Rate Swap
Debt Instrument [Line Items]
Derivative, average fixed interest rate	2.61%
Term loan facility | Term Loan A-1 Due August 2022
Debt Instrument [Line Items]
Term facility, maximum borrowing capacity	$ 1,800,000,000
Term of loan facility	5 years
Line of credit | Revolving line of credit
Debt Instrument [Line Items]
Term facility, maximum borrowing capacity	$ 700,000,000
Revolving line of credit, remaining borrowing capacity	700,000,000
Senior notes | 7.55% senior debentures due April 2028
Debt Instrument [Line Items]
Debt instrument, face amount							$ 100,000,000
Recurring | Interest Rate Swap
Debt Instrument [Line Items]
Asset for Swaps	18,542,000				11,985,000
Liability for Swaps	1,046,000
Level 2 | Recurring | Interest Rate Swap
Debt Instrument [Line Items]
Asset for Swaps	18,542,000				$ 11,985,000
Liability for Swaps	1,046,000
Level 2 | Recurring | Interest Rate Swap | Current Assets
Debt Instrument [Line Items]
Asset for Swaps	$ 1,600,000