Long-Term Debt (Narrative) (Details) - USD ($)	1 Months Ended	3 Months Ended			9 Months Ended
	May 31, 2019	Sep. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2025	Sep. 01, 2022	Aug. 31, 2022	Mar. 31, 2022	Oct. 01, 2021	Sep. 30, 2021	Apr. 30, 1998
Debt Instrument [Line Items]
Accrued interest expense		$ 100,000	$ 400,000		$ 100,000
Credit agreement, potential increase to term loan and line of credit	$ 300,000,000.0
Debt issuance costs	9,700,000
Debt issuance costs capitalized	9,600,000
Loss (gain) on extinguishment of debt			1,500,000
Unamortized costs	14,600,000
Debt issuance costs expensed		$ 1,200,000		$ 1,200,000	$ 3,710,000	$ 3,836,000
Derivative Instruments, Interest Rate Swaps, Percentage of Principle Balance		50.00%			50.00%
Liability for interest rate swap agreements			47,700,000
Interest expense, pre-tax		$ 7,100,000		(700,000)	$ (14,300,000)	(4,000,000.0)
Interest expense, pre-tax to be reclassified during next 12 months		16,000,000.0			16,000,000.0
Interest Rate Swap
Debt Instrument [Line Items]
Remaining notional balance		$ 1,200,000,000			$ 1,200,000,000
Derivative, average fixed interest rate		2.40%			2.40%
Asset for Swaps			$ 600,000
Interest Rate Swap | Cash Flow Hedges
Debt Instrument [Line Items]
Derivative liability		$ 87,700,000			$ 87,700,000
Interest Rate Swap | Minimum
Debt Instrument [Line Items]
Derivative, average fixed interest rate		0.66%			0.66%
Interest Rate Swap | Maximum
Debt Instrument [Line Items]
Derivative, average fixed interest rate		2.98%			2.98%
Interest Rate Swap | Forecast
Debt Instrument [Line Items]
Remaining notional balance							$ 465,000,000.0	$ 496,800,000	$ 1,000,000,000.0		$ 1,100,000,000	$ 1,200,000,000
Derivative, average fixed interest rate							2.64%		2.77%	2.59%
Swap
Debt Instrument [Line Items]
Market value adjustments on interest rate swaps, net of tax		$ 7,900,000		(8,100,000)	$ (30,500,000)	(41,400,000)
Deferred taxes on interest rate swaps		(2,600,000)		$ 2,700,000	10,100,000	$ 13,800,000
Line of Credit Due May 2024 | Revolving line of credit
Debt Instrument [Line Items]
Multicurrency revolving sub-facility	100,000,000.0
Line of Credit Due May 2024 | Letter of Credit
Debt Instrument [Line Items]
Revolving credit facility, letter of credit sub-facility	50,000,000.0
Term loan facility | Term Loan A-1 Due May 2024
Debt Instrument [Line Items]
Term facility, maximum borrowing capacity	$ 1,800,000,000
Term of loan facility	5 years
Line of Credit Due May 2024 | Revolving line of credit
Debt Instrument [Line Items]
Term facility, maximum borrowing capacity	$ 750,000,000.0
Term of loan facility	5 years
Revolving line of credit, remaining borrowing capacity		750,000,000.0			750,000,000.0
Senior notes | 7.55% senior debentures due April 2028
Debt Instrument [Line Items]
Debt instrument, face amount													$ 100,000,000.0
Accounts Payable and Accrued Liabilities
Debt Instrument [Line Items]
Derivative liability		$ 3,500,000			$ 3,500,000