Stock Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Company recognized total stock compensation expense, net of forfeitures	$ 36.1	$ 27.4	$ 22.1
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested, beginning balance	1,400,000	1,500,000
Nonvested, ending balance	1,400,000	1,400,000	1,500,000
Director Stock Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	$ 1.4	$ 1.3	$ 1.0
Intrinsic value of the unvested				$ 1,300,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	5 months
Number of shares granted	17,000	17,000	24,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized				$ 0.5
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested, beginning balance	22,000	24,000	26,000
Vested during period	(22,000)	(19,000)	(26,000)
Forfeited during period	0	0	0
Nonvested, ending balance	17,000	22,000	24,000
Restricted Share Activity [Roll Forward]
Nonvested, beginning balance, value	$ 1.6	$ 1.2	$ 1.2
Granted during period, value	1.5	1.4	1.2
Vested during period, value	(1.7)	(1.0)	(1.2)
Forfeited during period, value	0.0	0.0	0.0
Nonvested, ending balance, value	$ 1.6	$ 1.2	$ 1.2	$ 1.4
Market Based LTIA [Member] \| Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted	127,802	156,279	292,160
Grant Date Of Fair Value Of Shares Granted	$ 13.4	$ 14.1	$ 15.0
Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of the unvested				$ 66,300,000
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	1 year 8 months 12 days
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized				$ 33.7
Long Term Incentive Plan [Member] \| Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense	$ 32.2	$ 26.1	$ 21.1
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Nonvested, beginning balance	1,391,000	1,453,000	1,557,000
Granted during period	431,000	451,000	644,000
Vested during period	(393,000)	(465,000)	(655,000)
Forfeited during period	(125,000)	(48,000)	(93,000)
Nonvested, ending balance	1,304,000	1,391,000	1,453,000
Restricted Share Activity [Roll Forward]
Nonvested, beginning balance, value	$ 86.0	$ 73.4	$ 67.3
Granted during period, value	40.6	39.7	35.5
Vested during period, value	(24.2)	(24.1)	(25.0)
Forfeited during period, value	(8.4)	(3.0)	(4.4)
Nonvested, ending balance, value	$ 86.0	$ 73.4	$ 67.3	$ 94.0
Service Based LTIA [Member] \| Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares granted	303,638	295,482	352,053
Grant Date Of Fair Value Of Shares Granted	$ 27.3	$ 25.6	$ 20.4

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Restricted Share Activity [Roll Forward]

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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The total value of forfeitures related to restricted stock awards forfeited during the period.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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Per share or unit weighted-average intrinsic value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Net number of share options (or share units) granted during the period.

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Value, before forfeiture, of shares granted under share-based payment arrangement. Excludes employee stock ownership plan (ESOP).

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