| **Employee Stock And Incentive Plan (Narrative) (Details) - USD ($)**                            | 12 Months Ended         |
|--------------------------------------------------------------------------------------------------|-------------------------|
||
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**               |                    |   |   |
| Equity compensation plan, shares                                                                 | 231,502                 | 321,402 | 212,920 |
| 2009 Plan [Member]                                                                               |                    |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**               |                    |   |   |
| Number of shares authorized for issuance                                                         | 6,250,000               |   |   |
| Maximum number of shares available for issuance may be issued as restricted stock                | 3,125,000               |   |   |
| Maximum number of shares subject to grants to any one individual in any one year                 | 500,000                 |   |   |
| Underlying stock option and restricted stock awards available for grant                          | 3,952,869               |   |   |
| Performance Share Units [Member]                                                                 |                    |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**               |                    |   |   |
| Performance period specified in grant, in years                                                  | 3 years                 |   |   |
| Unrecognized compensation costs                                                                  | $ 5,444,000             |   |   |
| Period over which unrecognized compensation cost will be recognized                              | 1 year 9 months 18 days |   |   |
| Aggregate intrinsic value                                                                        | $ 15,582,000            |   |   |
| Equity compensation plan, shares                                                                 | 152,750                 |   |   |
| Weighted average fair value of stock awards granted                                              | $ 28.89                 |   |   |
| Matching contribution, annual profit sharing compensation expense                                | $ 3,823,000             | $ 4,419,000 | $ 4,996,000 |
| Performance Share Units [Member] | 2016 Grants [Member]                                          |                    |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**               |                    |   |   |
| PSUs will be earned based on the Company’s TSR                                             | 27.50%                  |   |   |
| PSUs will be earned based on maintaining an average ratio of operations and maintenance expenses | 25.00%                  |   |   |
| PSUs will be earned based on cumulative earnings before tax                                      | 20.00%                  |   |   |
| Performance Share Units [Member] | 2014 And 2015 Grants [Member]                                 |                    |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**               |                    |   |   |
| PSUs will be earned based on the Company’s TSR                                             | 30.00%                  |   |   |
| PSUs will be earned based on maintaining an average ratio of operations and maintenance expenses | 20.00%                  |   |   |
| PSUs will be earned based on cumulative earnings before tax                                      | 20.00%                  |   |   |
| Performance Share Units [Member] | Minimum [Member]                                              |                    |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**               |                    |   |   |
| Percentage of target award amount the grantee may earn                                           | 0.00%                   |   |   |
| Performance Share Units [Member] | Maximum [Member]                                              |                    |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**               |                    |   |   |
| Percentage of target award amount the grantee may earn                                           | 200.00%                 |   |   |
| Amortization period of fair value of shares, in months                                           | 36 months               |   |   |
| Vesting period, in years                                                                         | 3 years                 |   |   |
| Restricted Stock Units [Member]                                                                  |                    |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**               |                    |   |   |
| Unrecognized compensation costs                                                                  | $ 1,498,000             |   |   |
| Vesting period, in years                                                                         | 3 years                 |   |   |
| Period over which unrecognized compensation cost will be recognized                              | 1 year 9 months 18 days |   |   |
| Aggregate intrinsic value                                                                        | $ 3,283,000             |   |   |
| Equity compensation plan, shares                                                                 | 50,612                  |   |   |
| Weighted average fair value of stock awards granted                                              | $ 32.08                 | $ 26.00 | $ 24.80 |
| Matching contribution, annual profit sharing compensation expense                                | $ 1,061,000             | $ 1,076,000 | $ 1,122,000 |
| Stock Options [Member]                                                                           |                    |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**               |                    |   |   |
| Unrecognized compensation costs                                                                  | $ 0                     |   |   |
| Vesting period, in years                                                                         | 10 years                |   |   |
| Percentage of options exercisable annually                                                       | 33.00%                  |   |   |
| Number of options granted                                                                        | 0                       | 0 | 0 |
| Restricted Stock [Member]                                                                        |                    |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**               |                    |   |   |
| Unrecognized compensation costs                                                                  | $ 0                     |   |   |
| Intrinsic value of awards vested                                                                 |                    | $ 860,000 | $ 1,097,000 |
| Fair value of awards vested                                                                      |                    | $ 553,000 | $ 906,000 |
| Number of options granted                                                                        | 0                       | 0 |   |
| Weighted average fair value of stock awards granted                                              |                    |   | $ 25.19 |
| Matching contribution, annual profit sharing compensation expense                                |                    |   | $ 691,000 |
| Stock Awards [Member]                                                                            |                    |   |   |
| **Share-based Compensation Arrangement by Share-based Payment Award [Line Items]**               |                    |   |   |
| Equity compensation plan, shares                                                                 | 15,877                  |   |   |
| Weighted average fair value of stock awards granted                                              | $ 31.87                 | $ 26.44 |   |
| Matching contribution, annual profit sharing compensation expense                                | $ 506,000               | $ 365,000 |   |

| X                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         |
|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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.
+ References
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|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Unrecognized cost of unvested share-based compensation awards.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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).
+ References
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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).
+ References
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| - Definition
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.
+ References
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| - Definition
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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No definition available.
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| - Definition
The highest quantity of shares an employee can purchase under the plan per period.
+ References
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|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).
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|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
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.
+ References
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|----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Net number of share options (or share units) granted during the period.
+ References
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|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| - Definition
Percentage Earned Based On Cumulative Total Earning Before Tax
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| - Definition
Percentage Earned Based On Maintaining An Average Ratio Of Operations And Maintenance Expenses
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| - Definition
Percentage Earned Based On Total Shareholder Return
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| - Definition
Percentage of target award amount the participant may earn
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| - Definition
Performance Period Specified In Grant
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| - Definition
Share based compensation arrangement by share based payment award amortization period of fair value of shares
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| - Definition
Share Based Compensation Arrangement By Share Based Payment Award Equity Instruments Other Than Options Total Intrinsic Value
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| - Definition
Share based compensation arrangement by share based payment award equity instruments other than options vested in period total intrinsic value
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No definition available.
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| - Definition
Share Based Compensation Arrangement By Share Based Payment Award Maximum Number Of Shares Available For Issuance May Be Issued As Restricted Stock
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No definition available.
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| - Definition
Share Based Compensation Arrangement By Share Based Payment Award Percentage Of Options Exercisable Annually
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