COMMITMENTS AND CONTINGENCIES - Narrative (Details) $ in Millions	6 Months Ended
Jun. 30, 2018 USD ($) Bcf
Minimum
Construction, Drilling and Purchase Commitments
Oil and gas delivery commitments and contracts, period	1 month
Drilling Commitments
Construction, Drilling and Purchase Commitments
Commitments for purchases and other expenditures	$ 154.4
Gathering System Construction
Construction, Drilling and Purchase Commitments
Commitments for purchases and other expenditures	$ 14.4
Natural Gas Sales Contracts
Construction, Drilling and Purchase Commitments
Oil and gas delivery commitments and contracts, remaining contractual volume (bcf) \| Bcf	330.7
Oil and gas delivery commitments and contracts, period	6 years 7 months
Maximum financial commitment resulting from inability to meet gas delivery commitments	$ 659.9
Gas Gathering And Processing Agreements
Construction, Drilling and Purchase Commitments
Oil and gas delivery commitments and contracts, period	9 years 6 months
Maximum financial commitment resulting from inability to meet gas delivery commitments	$ 351.0
Minimum Volume Agreement
Construction, Drilling and Purchase Commitments
Maximum financial commitment resulting from inability to meet gas delivery commitments	7.4
Commitment liability	2.5
Other Transportation And Delivery Commitments And Facilities Commitments
Construction, Drilling and Purchase Commitments
Maximum financial commitment resulting from inability to meet gas delivery commitments	$ 26.6
Office Space
Construction, Drilling and Purchase Commitments
Operating lease term	8 years 2 months 1 day
Future minimum payments due on operating leases	$ 80.9
Compressor Equipment
Construction, Drilling and Purchase Commitments
Future minimum payments due on operating leases	$ 9.3
Compressor Equipment \| Minimum
Construction, Drilling and Purchase Commitments
Operating lease term	2 months
Compressor Equipment \| Maximum
Construction, Drilling and Purchase Commitments
Operating lease term	24 months

Term of lessee's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)(3)
-URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918673-209980

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Data Type:	xbrli:durationItemType
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Period Type:	instant

- Definition

The minimum amount the entity agreed to spend under the long-term purchase commitment.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of loss contingency liability.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 10
-Section 55
-Paragraph 40
-Subparagraph (Note 3)
-URI http://asc.fasb.org/extlink&oid=82846649&loc=d3e38371-112697

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 840
-SubTopic 20
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77902758&loc=d3e41502-112717

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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

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

+ References

No definition available.

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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.

+ References

No definition available.

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