Stock-Based Compensation and Directors Stock Purchase Plan (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining number of shares available for issuance under the plan	3,018,432
Stock-based compensation	$ 11.5	$ 10.1	$ 8.8
Total tax benefit recognized from compensation arrangements	4.3	3.8	3.3
New Accounting Pronouncement or Change in Accounting Principle, Cumulative Effect of Change on Equity or Net Assets	1.3
Fair value of shares vested during the period	10.9	$ 6.0	$ 4.5
Unrecognized compensation cost related to unvested options, SAR's and stock awards	$ 18.8
Compensation cost is expected to be recognized over a weighted average period, years	2 years 7 months
Common stock dividend rate percentage	5.00%
Nonvested Stock Award [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period (in years)	4 years
Nonvested Stock Award [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period (in years)	7 years
Stock Appreciation Rights (SARs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock awards vesting period (in years)	4 years
Contractual terms of awards granted (in years)	10 years
Directors Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining number of shares available for issuance under the plan	91,667
Number of shares purchased under stock option plan	20,541	24,596
Average price of shares purchased under stock option plan	$ 44.63	$ 39.62

Common stock dividend rate percentage.

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Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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Unrecognized cost of unvested share-based compensation awards.

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The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

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Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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The weighted average of per share prices paid for shares purchased on the open market for issuance to employees under the plan.

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The number of shares purchased on the open market during the period for issuance to employees under the plan.

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Weighted average remaining contractual term for fully vested and expected to vest options that are exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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