LONG-TERM DEBT - Summary (Details) - USD ($) $ in Thousands	Jun. 30, 2016	Dec. 31, 2015
Debt Instrument
Principal	$ 1,500,000	$ 1,500,000
Unamortized Debt Issuance Costs	13,205	14,380
Senior Notes 5.875% [Member]
Debt Instrument
Principal	750,000	750,000
Unamortized Debt Issuance Costs	$ 6,324	$ 6,978
Interest rate (as a percent)	5.875%	5.875%
Senior Notes 4.375% [Member]
Debt Instrument
Principal	$ 750,000	$ 750,000
Unamortized Debt Issuance Costs	$ 6,881	$ 7,402
Interest rate (as a percent)	4.375%	4.375%

Amount of long-term debt before deduction of unamortized discount or premium. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt, with initial maturities beyond one year or the normal operating cycle, if longer.

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)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 20
-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 16
-Article 9

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- Definition

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

+ 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.

+ References

No definition available.

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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

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