Acquisition and Disposition of Properties - Additional Information (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016
Gas and Oil Acreage [Line Items]
Payment for unproved leasehold	$ 235.6	$ 27.2
Delaware Basin
Gas and Oil Acreage [Line Items]
Payment for unproved leasehold	185.9
Midland Basin
Gas and Oil Acreage [Line Items]
Payment for unproved leasehold	30.9
Mineral Purchases
Gas and Oil Acreage [Line Items]
Payment for unproved leasehold	18.8
Disposal group \| Permian and San Juan Basin
Gas and Oil Acreage [Line Items]
Amount of consideration received	552.0
Held-for-sale \| Permian and San Juan Basin
Gas and Oil Acreage [Line Items]
Proceeds from sale of oil and gas property and equipment	532.5
Purchase price adjustments	19.0
Transaction costs	5.0
Pre-tax gain on disposal	246.0	$ 161.1
Purchase price adjustments	$ 0.2

Disposal Group, Not Discontinued Operation, Post Closing Adjustment Gain (Loss) on Disposal

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- Definition

Disposal Group, Not Discontinued Operation, Purchase Price Adjustments

+ References

No definition available.

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Disposal Group, Not Discontinued Operation, Transaction Costs

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- Definition

Payments To Acquire Unproved Leasehold Properties

+ References

No definition available.

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- Definition

Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation.

+ References

No definition available.

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- Definition

Amount before tax of gain (loss) recognized on the sale or disposal of a disposal group. Excludes discontinued operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2443-110228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=64862545&loc=d3e2941-110230

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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 cash inflow to dispose of long-lived, physical assets and mineral interests in oil and gas properties used for normal oil and gas operations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Investing Activities
-URI http://asc.fasb.org/extlink&oid=6516133

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 12
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3179-108585

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