Equity Incentive Plans (Summary Of Restricted Share Unit Activity) (Details) $ / shares in Units, $ in Millions	9 Months Ended
Sep. 30, 2020 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Number of Shares, Outstanding at December 31, 2019 \| shares	509,338
Number of Shares, Granted \| shares	211,549
Number of Shares, Vested \| shares	(228,557)
Number of Shares, Outstanding at June 30, 2020 \| shares	487,739
Weighted Average Grant Date Fair Value, Outstanding at December 31, 2019 \| $ / shares	$ 67.88
Weighted Average Grant Date Fair Value, Granted \| $ / shares	69.09
Weighted Average Grant Date Fair Value, Vested \| $ / shares	67.76
Weighted Average Grant Date Fair Value, Outstanding at June 30, 2020 \| $ / shares	$ 68.46
Unamortized share-based compensation expense \| $	$ 15.5
Weighted Average Life Remaining, Outstanding at June 30, 2020 (in years)	1 year 21 days
Restricted Share Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Number of Shares, Outstanding at December 31, 2019 \| shares	26,236
Number of Shares, Granted \| shares	74,767
Number of Shares, Vested \| shares	(26,236)
Number of Shares, Outstanding at June 30, 2020 \| shares	74,767
Weighted Average Grant Date Fair Value, Outstanding at December 31, 2019 \| $ / shares	$ 77.54
Weighted Average Grant Date Fair Value, Granted \| $ / shares	31.57
Weighted Average Grant Date Fair Value, Vested \| $ / shares	77.54
Weighted Average Grant Date Fair Value, Outstanding at June 30, 2020 \| $ / shares	$ 31.57
Unamortized share-based compensation expense \| $	$ 1.6
Weighted Average Life Remaining, Outstanding at June 30, 2020 (in years)	8 months 1 day

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

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-Name Accounting Standards Codification
-Topic 718
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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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The weighted average fair value at grant date for nonvested equity-based awards issued 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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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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

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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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