Represents the period of extension to the maturity of debt instrument.

No definition available.

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- Definition

Represents the number of extensions to the maturity of debt instrument.

+ References

No definition available.

+ Details

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- Definition

Represents the facility fee that is payable quarterly on the full amount of the commitments under the facility based on the entity's current credit ratings.

+ References

No definition available.

+ Details

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- Definition

Represents the amount of additional borrowing capacity under the credit facility.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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- Definition

Represents the amount of the borrowing capacity under the credit facility used to back up outstanding commercial paper borrowings.

+ References

No definition available.

+ Details

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- Definition

Represents the aggregate amount of default by the entity on other indebtedness subject to the cross-default provisions of the credit facility agreement.

+ References

No definition available.

+ Details

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- Definition

Represents the actual interest coverage ratio at the end of the reporting period.

+ References

No definition available.

+ Details

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- Definition

Represents the maximum debt to capital ratio allowable under the financial covenant.

+ References

No definition available.

+ Details

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- Definition

Represents the minimum interest coverage ratio allowable under the financial covenant.

+ References

No definition available.

+ Details

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- Definition

The average effective interest rate on short term debt during the reporting period.

+ References

No definition available.

+ Details

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

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- Definition

Amount borrowed under the credit facility as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

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- Definition

The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 15

-Subparagraph (e)

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than one year or the normal operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 13

-Subparagraph 2, 3

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- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, average borrowings during the period.

+ References

No definition available.

+ Details

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- Definition

For the form of debt having an initial term of less than one year or less than the normal operating cycle, if longer, maximum month-end borrowings during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Industry Guide

-Number 3

-Section VII

-Subsection 2

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- Definition

Weighted average interest rate of short-term debt outstanding.

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-Publisher FASB

-Name Accounting Standards Codification

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-SubTopic 10

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SHORT-TERM BORROWINGS (Details) (USD $)	12 Months Ended			0 Months Ended
SHORT-TERM BORROWINGS (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 20, 2014 item	Oct. 19, 2014
Short-Term Borrowings
Short-term borrowings	$ 44,000,000us-gaap_ShortTermBorrowings	$ 4,000,000us-gaap_ShortTermBorrowings
Average borrowings outstanding	30,000,000	8,700,000
Highest month-end balances	77,000,000	29,000,000
Weighted average interest rate during period (as a percent)	0.38	0.69
Weighted average interest rate at year end (as a percent)	0.44%	0.33%
Debt issuance costs	651,000us-gaap_PaymentsOfDebtIssuanceCosts	1,879,000us-gaap_PaymentsOfDebtIssuanceCosts	1,074,000us-gaap_PaymentsOfDebtIssuanceCosts
Commercial paper
Short-Term Borrowings
Short-term borrowings	44,000,000
Outstanding borrowings	0
Amount of credit facility used to back up outstanding commercial paper borrowings	44,000,000
Unsecured revolving credit facility
Short-Term Borrowings
Unsecured revolving credit facility				200,000,000	150,000,000
Maturity term				5 years
Number of extensions				2
Extension period				1 year
Facility fee is payable quarterly on the full amount of the commitments under the facility based on our current credit ratings (as a percent)	0.175%
Debt issuance costs	300,000
Maximum percentage of total indebtedness to total capitalization under the financial covenants of the credit facility agreement	65.0
Minimum interest coverage ratio based on EBITDA under the financial covenants of the credit facility agreement	0.52
EBITDA coverage ratio over interest charges	1.0
Aggregate amount of default on other indebtedness subject to cross-default under the terms of the credit facility.	25,000,000
Outstanding borrowings	0
Unsecured revolving credit facility \| Federal fund effective rate
Short-Term Borrowings
Margin over the base rate (as a percent)	0.50%
Unsecured revolving credit facility \| One month LIBOR
Short-Term Borrowings
Description of interest rate basis	one month LIBOR
Margin over the base rate (as a percent)	1.00%
Unsecured revolving credit facility \| One month, two month or three month LIBOR
Short-Term Borrowings
Description of interest rate basis	one month, two month, three month or six month LIBOR
Margin over the base rate (as a percent)	1.025%
Letters of credit
Short-Term Borrowings
Unsecured revolving credit facility				20,000,000
Additional borrowing capacity	75,000,000
Swingline loan
Short-Term Borrowings
Unsecured revolving credit facility				$ 20,000,000