Share-Based Compensation, TSR Liability Awards (Details) shares in Thousands, $ in Thousands	12 Months Ended
Dec. 31, 2018 USD ($) Parties shares	Dec. 31, 2017 USD ($) shares	Dec. 31, 2016 USD ($) shares
Equity Instruments Other than Options Activity [Roll Forward]
Granted (in shares)	500	503	522
Equity Instruments Other than Options, Additional Disclosures [Abstract]
Award Vesting Period (in years)	3 years
Number of Utilities in Peer Group \| Parties	22
TSR Liability Awards
Equity Instruments Other than Options Activity [Roll Forward]
Granted (in shares)	239	240	264
Equity Instruments Other than Options, Additional Disclosures [Abstract]
Award Vesting Period (in years)	3 years
Amount of cash used to settle TSR liability awards \| $	$ 8,000
Awards settled (in shares)	482	454	354
Settlement amount (cash and common stock) \| $	$ 21,534	$ 19,083	$ 13,724
TSR Liability Awards \| Minimum
Equity Instruments Other than Options, Additional Disclosures [Abstract]
Percentage payout for TSR liability awards	0.00%
TSR Liability Awards \| Maximum
Equity Instruments Other than Options, Additional Disclosures [Abstract]
Percentage payout for TSR liability awards	200.00%

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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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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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

Aggregate value of cash and stock paid by the entity during the period to settle performance share plan (PSP) awards granted under the Company's long-term incentive plan.

+ References

No definition available.

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Aggregate cash paid by the entity during the period to settle liability instruments granted under share-based payment arrangements.

+ References

No definition available.

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- Definition

Number of Utilities in Peer Group

+ References

No definition available.

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- Definition

Percentage payout for performance share plan (PSP) liability awards.

+ References

No definition available.

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- Definition

The number of units/shares settled under a share-based award plan during the period in cash or stock.

+ References

No definition available.

+ Details

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