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Fair Value Measurements - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net derivative asset	$ (300,000)	$ (600,000)
Fair value, assets, level 1 to 2 transfer, amount	0	0
Fair value, assets, level 2 to 1 transfer, amount	0	0
Long-term debt, carrying value	2,302,584,000	2,670,664,000
Asset retirement obligation, carrying value	35,812,000	42,549,000	$ 36,458,000
Impairment of oil and gas properties	$ 46,109,000	47,238,000	1,168,000
Proved oil and gas properties
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impairment of oil and gas properties		40,000,000	0
Number of years where NYMEX forward swap prices were used	5 years
Inflation factor for estimated future cash flows after five years	3.00%
Inflation factor applied to the future operating and development costs after five years	3.00%
Number of years for use of inflation factor to determine the future operating and development costs	5 years
Proved oil and gas properties | Assets held for sale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impairment of oil and gas properties	$ 9,400,000
Unproved oil and gas properties
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Impairment of oil and gas properties	36,600,000	7,300,000	$ 1,200,000
Carrying value | Proved oil and gas properties
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of property	25,900,000	76,400,000
Fair value | Proved oil and gas properties
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value of property	16,500,000	$ 36,400,000
Senior unsecured notes
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term, unsecured notes and borrowings	2,200,000,000
Long-term debt, fair value	1,440,000,000
Amended credit facility
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term line of credit	$ 138,000,000

X

- Definition

Fair Value Input, Inflation Factor For Estimated Cash flows

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Fair Value Input, Inflation Factor For Estimated Operating and Development Costs

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- Definition

Fair Value Input, Number of Years For Use of Inflation Factor

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No definition available.

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- Definition

Fair Value Input, Number of Years Using NYMEX Forward Swap Prices

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No definition available.

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- Definition

The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 410
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (c)
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=6505190

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Amount of credit risk valuation adjustment to derivative assets to properly reflect the credit quality of the counterparties.

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No definition available.

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- Definition

Amount of transfers of assets measured on a recurring basis out of Level 1 of the fair value hierarchy into Level 2.

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bb)
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Amount of transfers of assets measured on a recurring basis out of Level 2 of the fair value hierarchy into Level 1.

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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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- Definition

The expense recorded to reduce the value of oil and gas assets consisting of proved properties and unproved properties as the estimate of future successful production from these properties is reduced.

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-Publisher FASB
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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

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Carrying amount of long-term debt, net of unamortized discount or premium, including current and noncurrent amounts. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Fair value portion of physical assets used in the normal conduct of business to produce goods and services and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, and furniture and fixtures.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
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