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Long-Term Debt - Additional Information (Detail) (USD $) | 3 Months Ended | 6 Months Ended | 24 Months Ended | 6 Months Ended |  |  | 6 Months Ended | 0 Months Ended | 24 Months Ended |
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Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 Senior Unsecured Debt [Member] | Dec. 31, 2012 Senior Unsecured Debt [Member] | Jun. 30, 2014 Second Amended Credit Facility [Member] | Mar. 27, 2014 Second Amended Credit Facility [Member] | Apr. 05, 2013 Second Amended Credit Facility [Member] | Jun. 30, 2014 Current Ratio [Member] Second Amended Credit Facility [Member] | Jun. 30, 2014 Minimum [Member] Second Amended Credit Facility [Member] | Sep. 24, 2013 2022 Notes [Member] Senior Unsecured Debt [Member] | Dec. 31, 2012 2019 Notes [Member] Senior Unsecured Debt [Member] | Dec. 31, 2012 2021 Notes [Member] Senior Unsecured Debt [Member] | Dec. 31, 2012 2023 Notes [Member] Senior Unsecured Debt [Member] | Dec. 31, 2013 2023 Notes [Member] Senior Unsecured Debt [Member]
Debt Disclosure [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Principal debt amount |  |  |  |  |  |  |  |  |  |  |  | $ 1,000,000,000.0 | $ 400,000,000.0 | $ 400,000,000.0 |  | $ 400,000,000.0
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  | 6.875% | 7.25% | 6.50% |  | 6.875%
Debt instrument, maturity date |  |  |  |  |  |  | Apr. 05, 2018 |  |  |  |  | Mar. 15, 2022 | Feb. 01, 2019 | Nov. 01, 2021 | Jan. 15, 2023 |
Net proceeds from issuance of notes |  |  |  |  |  | 1,175,800,000 |  |  |  |  |  | 983,600,000 |  |  |  |
Exchange term |  |  |  |  |  |  |  |  |  |  |  | 360 days |  |  |  |
Exchange increase in interest rate |  |  |  |  |  |  |  |  |  |  |  | 1.00% |  |  |  |
Line of credit facility maximum increase to aggregate commitments |  |  |  |  |  |  |  | 1,750,000,000 | 1,500,000,000 |  |  |  |  |  |  |
Senior unsecured notes payment frequency |  |  |  |  | semi-annually |  |  |  |  |  |  |  |  |  |  |
Redemption percentage, maximum |  |  |  |  | 35.00% |  |  |  |  |  |  |  |  |  |  |
Redemption term |  |  |  |  | 180 days |  |  |  |  |  |  |  |  |  |  |
Percentage of minimum outstanding principal amount |  |  |  |  | 65.00% |  |  |  |  |  |  |  |  |  |  |
Event of default by payment default ($10.0 million or more) |  |  |  |  | 10,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Event of default by final judgments (in excess of $10.0 million) |  |  |  |  | 10,000,000.0 |  |  |  |  |  |  |  |  |  |  |
Line of credit facility, maximum borrowing capacity |  |  |  |  |  |  |  | 1,500,000,000.0 |  |  |  |  |  |  |  |
Line of credit facility, capacity available for specific purpose other than for trade purchases |  |  |  |  |  |  | 2,500,000,000 |  |  |  |  |  |  |  |  |
Percentage of the reserve value of assets as determined by reserve reports (at least 80%) |  |  |  |  |  |  |  |  |  |  | 80.00% |  |  |  |  |
Commitment fee of borrowing base capacity not utilized |  |  |  |  |  |  | 0.375% |  |  |  |  |  |  |  |  |
Ratio of EBITDAX to interest expense necessary to maintain covenants |  |  |  |  |  |  |  |  |  |  | 2.5 |  |  |  |  |
Minimum current ratio |  |  |  |  |  |  |  |  |  | 1.0 |  |  |  |  |  |
Line of credit facility, amount outstanding |  |  |  |  |  |  | 100,000,000 |  |  |  |  |  |  |  |  |
Outstanding letters of credit |  |  |  |  |  |  | 5,200,000 |  |  |  |  |  |  |  |  |
Line of credit facility, remaining borrowing capacity |  |  |  |  |  |  | 1,394,800,000 |  |  |  |  |  |  |  |  |
Weighted average interest rate |  |  |  |  |  |  | 1.70% |  |  |  |  |  |  |  |  |
Deferred financing costs | 38,700,000 |  | 38,700,000 |  |  |  |  |  |  |  |  |  |  |  |  |
Amortization of deferred financing costs | $ 1,600,000 | $ 1,000,000 | $ 3,200,000 | $ 1,900,000 |  |  |  |  |  |  |  |  |  |  |  |

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- Definition Date when the debt instrument is scheduled to be fully repaid, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(2)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition For an unclassified balance sheet, the carrying amount (net of accumulated amortization) as of the balance sheet date of capitalized costs associated with the issuance of debt instruments (for example, legal, accounting, underwriting, printing, and registration costs) that will be charged against earnings over the life of the debt instruments to which such costs pertain. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28555-108399 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.17) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 17 -Article 5 + Details
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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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.16) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 20, 22 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-03.16) -URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910 + Details
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- Definition Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility. + References 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 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
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- Definition Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding). + References 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 210.5-02.19(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
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- Definition The cash inflow from the issuance of long-term debt that is not secured by collateral. Excludes proceeds from tax exempt unsecured debt. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585 + Details
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