COMMITMENTS AND CONTINGENCIES - Other Commitments - Delivery, operating leases (Details) $ in Millions	3 Months Ended
Mar. 31, 2017 USD ($) Bcf
Non-cancelable operating leases
Future minimum operating lease arrangements	$ 94.3
Natural Gas Sales Contracts [Member]
Delivery Commitments
Volume of gas deliverable (in Bcf) \| Bcf	64.4
Delivery term	19 months
Financial commitment upon nondelivery	$ 169.4
Gas Gathering And Processing Agreements [Member]
Delivery Commitments
Delivery term	9 years
Financial commitment upon nondelivery	$ 242.4
Minimum Volume Agreement [Member]
Delivery Commitments
Financial commitment upon nondelivery	7.4
Accrued liabilities	2.1
Other Transportation, Delivery And Facilities Commitments [Member]
Delivery Commitments
Financial commitment upon nondelivery	$ 41.4

Carrying value as of the balance sheet date of obligations incurred and payable, pertaining to costs that are statutory in nature, are incurred on contractual obligations, or accumulate over time and for which invoices have not yet been received or will not be rendered. Examples include taxes, interest, rent and utilities. Used to reflect the current portion of the liabilities (due within one year or within 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 210.5-02.20)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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

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- Definition

Total amount of product committed to be supplied under existing contracts or agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-K (SK)
-Number 229
-Section 1207
-Paragraph (a)
-Subparagraph (2)

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- Definition

Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 10
-Section 55
-Paragraph 40
-Subparagraph (Note 3)
-URI http://asc.fasb.org/extlink&oid=6584154&loc=d3e38371-112697

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6453985&loc=d3e41502-112717

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- Definition

Total financial obligation resulting from inability to meet short-term or long-term contractual delivery obligations.

+ References

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- Definition

This element represents the period for delivery of oil and gas under terms of contracts and agreements in effect at balance sheet date.

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