Maximum Value Of Stock Employees Are Allowed To Purchase

No definition available.

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- Definition

The period of time after acquiring shares in which the owner can do a cashless exchange.

+ References

No definition available.

+ Details

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- Definition

The period of time over which an award is earned.

+ References

No definition available.

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- Definition

The target number of shares to be awarded under the plan if performance goals are achieved.

+ References

No definition available.

+ Details

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- Definition

The number of shares available for grant under the plan for any type of authorized award.

+ References

No definition available.

+ Details

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- Definition

The maximum vesting term over 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.

+ References

No definition available.

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- 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.

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The amount of expense, net of income tax, 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

No definition available.

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- Definition

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

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- Definition

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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- Definition

Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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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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- Definition

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

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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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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).

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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).

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- Definition

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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- Definition

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

+ References

No definition available.

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- Definition

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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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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No definition available.

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- Definition

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

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- Definition

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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- 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.

+ References

No definition available.

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- Definition

Net number of non-option equity instruments granted to participants.

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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

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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- Definition

For presentations that combine terminations, the number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan or that expired.

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- Definition

Weighted average price of options that were either forfeited or expired.

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- Definition

Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

+ References

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- Definition

Number of options outstanding, including both vested and non-vested options.

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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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No definition available.

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- Definition

Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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- References

No definition available.

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- Definition

Weighted average price at which option holders acquired shares when converting their stock options into shares.

+ References

No definition available.

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- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for vested portions of options outstanding and currently 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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- Definition

Purchase price of common stock expressed as a percentage of its fair value.

+ References

No definition available.

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- Definition

Number of share options (or share units) exercised during the current period.

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Number of shares that have been repurchased during the period and are being held in treasury.

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=84159872&loc=d3e21463-112644

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6405813&loc=d3e23239-112655

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
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Stock-Based Compensation (Details) - USD ($)	12 Months Ended			24 Months Ended	36 Months Ended
Stock-Based Compensation (Details) - USD ($)	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from Stock Options Exercised	$ 4,819,000	$ 8,404,000	$ 3,875,000
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	(930,000)	(924,000)	(1,012,000)
Allocated Share-based Compensation Expense, Net of Tax	1,424,000	1,446,000	1,661,000
Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount	$ 528,000	$ 554,000	$ 661,000
Long Term Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	1,100,000			1,100,000	1,100,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant, Any Award Type	626,960			626,960	626,960
Number of RSUs [Roll Forward]
Nonvested, beginning of period	0
Nonvested, end of period	0	0		0	0	0
Long Term Incentive Plan [Member] \| Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Arrangement by Share Based Payment Award Performance Period	3 years
Share Based Compensation Award Target Share	87,473			87,473	87,473
Unrecognized compensation expense	$ 2,800,000			$ 2,800,000	$ 2,800,000
Unrecognized Compensation Cost, Period for Recognition	through 2019.
Allocated Share-based Compensation Expense	$ 933,000
Weighted Average Price Per LTIP
Nonvested, beginning of period	$ 50.83
Granted	57.05
Vested	52.02
Nonvested, end of period	$ 56.40	$ 50.83		$ 56.40	$ 56.40	$ 50.83
Long Term Incentive Plan [Member] \| Performance Shares [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	174,946			174,946	174,946
Long Term Incentive Plan [Member] \| Performance Shares [Member] \| A 2014 Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted		31,388
Allocated Share-based Compensation Expense		$ 168,000				$ 1,685,000
Long Term Incentive Plan [Member] \| Performance Shares [Member] \| 2015-2017 Grant
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	29,967			29,967	29,967
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted	18,300
Allocated Share-based Compensation Expense	$ (346,000)				$ 1,169,000
Long Term Incentive Plan [Member] \| Performance Shares [Member] \| 2015-2017 Grant \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	59,934			59,934	59,934
Long Term Incentive Plan [Member] \| Performance Shares [Member] \| A 2016 Award [Member] [Domain]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	24,826			24,826	24,826
Allocated Share-based Compensation Expense	$ 337,000			$ 815,000
Long Term Incentive Plan [Member] \| Performance Shares [Member] \| A 2016 Award [Member] [Domain] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	49,652			49,652	49,652
Long Term Incentive Plan [Member] \| Performance Shares [Member] \| A 2017 Award [Member] [Domain] [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	32,680			32,680	32,680
Allocated Share-based Compensation Expense	$ 942,000
Long Term Incentive Plan [Member] \| Performance Shares [Member] \| A 2017 Award [Member] [Domain] [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share Based Compensation Award Target Share	65,360			65,360	65,360
Long Term Incentive Plan [Member] \| Performance Shares [Member] \| A 2013 Award [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted			8,914
Allocated Share-based Compensation Expense			$ 312,000				$ 1,240,000
Long Term Incentive Plan [Member] \| Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense	$ 3,100,000			$ 3,100,000	$ 3,100,000
Unrecognized Compensation Cost, Period for Recognition	through 2022
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	4 years
Allocated Share-based Compensation Expense	$ 1,600,000	$ 1,500,000	$ 1,300,000
Number of RSUs [Roll Forward]
Nonvested, beginning of period	89,973	88,587	70,794	88,587	70,794
Granted	32,168	40,271	37,264
Vested	(35,341)	(29,488)	(19,003)
Forfeit	(2,278)	(9,397)	(468)
Nonvested, end of period	84,522	89,973	88,587	84,522	84,522	89,973	88,587
Weighted Average Price Per LTIP
Nonvested, beginning of period	$ 48.85	$ 44.78	$ 44.00	$ 44.78	$ 44.00
Granted	60.51	54.36	46.29
Vested	47.07	45.56	44.81
Forfeited	53.78	44.59	44.99
Nonvested, end of period	$ 53.90	$ 48.85	44.78	$ 53.90	$ 53.90	$ 48.85	$ 44.78
Restated Stock Option Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from Stock Options Exercised	$ 3,900,000
Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period	10 years 7 days
Share Based Compensation Arrangement By Share Based Payment Award Exchange Period	6 months
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	2 years 5 months 18 days
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense	$ 500,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price	$ 41.15		$ 45.74
Option Shares
Exercised	(88,275)	(172,525)	(62,900)
Forfeited	(200)	0	(500)
Balance outstanding, end of period	91,688	180,163	352,688	91,688	91,688	180,163	352,688
Weighted-Average Price Per Share
Balance outstanding, beginning of period	$ 44.38	$ 44.00	$ 43.40	$ 44.00	$ 43.40
Exercised	44.33	43.61	39.96
Balance outstanding, end of period	$ 44.43	$ 44.38	$ 44.00	$ 44.43	$ 44.43	$ 44.38	$ 44.00
Intrinsic Value balance, beginning of period	$ 2,800,000	$ 2,300,000	$ 2,700,000	$ 2,300,000	$ 2,700,000
Intrinsic value, Exercised	1,800,000	2,000,000	500,000
Intrinsic Value balance, end of period	$ 1,400,000	2,800,000	2,300,000	$ 1,400,000	$ 1,400,000	$ 2,800,000	$ 2,300,000
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percent Of Offering Date Price Employees Are Allowed To Purchase Stock	85.00%
Maximum Value Of Stock Employees Are Allowed To Purchase	$ 21,199
Operations and Maintenance Expense [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense	$ 2,354,000	$ 2,370,000	$ 2,673,000
Stock Repurchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Treasury Stock, Shares, Acquired	0
Stock Repurchase Plan [Member] \| Repurchases Since Plan Inception in Year 2000 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Treasury Stock, Shares, Acquired	2,100,000
Treasury Stock, Value, Acquired, Cost Method	$ 83,300,000