LONG-TERM DEBT (Details) - USD ($)	3 Months Ended
Mar. 31, 2016	Dec. 31, 2015
Debt Instrument
Unamortized debt issuance costs	$ 13,789,000	$ 14,380,000
Revolving Credit Facility [Member]
Debt Instrument
Unamortized debt issuance costs	5,400,000	5,700,000
Credit facility amount	1,000,000,000
Credit facility, increase amount option	1,250,000,000
Borrowings outstanding	0
Letters of credit outstanding under the credit facility	2,500,000
Unused borrowing availability	$ 997,500,000
Debt-to-Capital ratio	65.00%
Revolving Credit Facility [Member] \| Minimum [Member]
Debt Instrument
Commitment fee percentage	0.125%
Revolving Credit Facility [Member] \| Maximum [Member]
Debt Instrument
Commitment fee percentage	0.35%
Senior Notes 4.375% [Member]
Debt Instrument
Unamortized debt issuance costs	$ 7,140,000	$ 7,402,000
Interest rate (as a percent)	4.375%	4.375%
Effective rate	4.50%
Senior Notes 5.875% [Member]
Debt Instrument
Unamortized debt issuance costs	$ 6,649,000	$ 6,978,000
Interest rate (as a percent)	5.875%	5.875%
Effective rate	6.04%
London Interbank Offered Rate (LIBOR) [Member] \| Revolving Credit Facility [Member] \| Minimum [Member]
Debt Instrument
Interest rate margin (as a percent)	1.125%
London Interbank Offered Rate (LIBOR) [Member] \| Revolving Credit Facility [Member] \| Maximum [Member]
Debt Instrument
Interest rate margin (as a percent)	2.00%
Base Rate [Member] \| Revolving Credit Facility [Member] \| Minimum [Member]
Debt Instrument
Interest rate margin (as a percent)	0.125%
Base Rate [Member] \| Revolving Credit Facility [Member] \| Maximum [Member]
Debt Instrument
Interest rate margin (as a percent)	1.00%

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

No definition available.

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

+ Details

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

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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.

+ Details

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- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

+ Details

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- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

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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

+ Details

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- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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- Definition

The fee, expressed as a percentage of the line of credit facility, for available but unused credit capacity under the credit facility.

+ References

No definition available.

+ Details

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- Definition

The remaining balance of debt issuance expenses that were capitalized and are being amortized against income over the lives of the respective bond issues. This does not include the amounts capitalized as part of the cost of the utility plant or asset.

+ References

+ Details

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- Definition

Debt To Capital Ratio

+ References

No definition available.

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