Acquisition and Disposition of Properties - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2017	Mar. 31, 2016
Gas and Oil Acreage [Line Items]
Payment for unproved leasehold	$ 157.8	$ 7.6
Delaware Basin
Gas and Oil Acreage [Line Items]
Payment for unproved leasehold	111.9
Midland Basin
Gas and Oil Acreage [Line Items]
Payment for unproved leasehold	27.1
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	532.6
Purchase price adjustments	19.0
Transaction costs	5.0
Pre-tax gain on disposal	$ 246.0

Disposal Group, Not Discontinued Operation, Purchase Price Adjustments

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Payments To Acquire Unproved Leasehold Properties

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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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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.

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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
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-Section 45
-Paragraph 12
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-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3179-108585

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