Long-Term Debt (Details) (USD $) | 3 Months Ended | 6 Months Ended | | 12 Months Ended | | | | 1 Months Ended | | 12 Months Ended | | | 6 Months Ended | 12 Months Ended | | | 6 Months Ended | 1 Months Ended | | 6 Months Ended |
Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 | Jun. 30, 2013 | Dec. 31, 2013 | Dec. 31, 2012 | Jun. 30, 2014 | Dec. 31, 2013 | Nov. 30, 2011 | 31-May-12 | 17-May-12 | Dec. 31, 2013 | Jun. 30, 2014 | Jan. 31, 2013 | Jun. 30, 2014 | Dec. 31, 2013 | Jun. 30, 2014 | Jul. 26, 2013 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jul. 31, 2014 | Jul. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 | Jun. 30, 2014 |
8.125% Senior Notes due December 2019 | 8.125% Senior Notes due December 2019 | 8.125% Senior Notes due December 2019 | 8.125% Senior Notes due December 2019 | 8.125% Senior Notes due December 2019 Additional | 8.125% Senior Notes due December 2019 Additional | 5.50% Senior Notes due January 2021 | 5.50% Senior Notes due January 2021 | 5.50% Senior Notes due January 2021 | Senior Notes | 5.50% Senior Notes due February 2022 | 5.50% Senior Notes due February 2022 | 5.50% Senior Notes due February 2022 | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsequent Event | Subsequent Event | Debt Instrument Borrowing Base Utilization Less than 25 Percent | Debt Instrument Borrowing Base Utilization Less than 25 Percent | Debt Instrument Borrowing Base Utilization Less than 25 Percent | Debt Instrument Borrowing Base Utilization Less than 25 Percent | Debt Instrument, Borrowing Base Utilization Greater than Equal to 25 Percent and Less than 50 Percent | Debt Instrument, Borrowing Base Utilization Greater than Equal to 25 Percent and Less than 50 Percent | Debt Instrument, Borrowing Base Utilization Greater than Equal to 25 Percent and Less than 50 Percent | Debt Instrument, Borrowing Base Utilization Greater than Equal to 25 Percent and Less than 50 Percent | Debt Instrument, Borrowing Base Utilization Greater than Equal to 25 Percent and Less than 50 Percent | Debt Instrument Borrowing Base Utilization Greater than Equal to 50 Percent and Less than 75 Percent | Debt Instrument Borrowing Base Utilization Greater than Equal to 50 Percent and Less than 75 Percent | Debt Instrument Borrowing Base Utilization Greater than Equal to 50 Percent and Less than 75 Percent | Debt Instrument Borrowing Base Utilization Greater than Equal to 50 Percent and Less than 75 Percent | Debt Instrument Borrowing Base Utilization Greater than Equal to 50 Percent and Less than 75 Percent | Debt Instrument Borrowing Base Utilization Greater than Equal to 75 Percent and Less than 90 Percent | Debt Instrument Borrowing Base Utilization Greater than Equal to 75 Percent and Less than 90 Percent | Debt Instrument Borrowing Base Utilization Greater than Equal to 75 Percent and Less than 90 Percent | Debt Instrument Borrowing Base Utilization Greater than Equal to 75 Percent and Less than 90 Percent | Debt Instrument Borrowing Base Utilization Greater than Equal to 75 Percent and Less than 90 Percent | Debt Instrument, Borrowing Base Utilization Greater than 90 Percent | Debt Instrument, Borrowing Base Utilization Greater than 90 Percent | Debt Instrument, Borrowing Base Utilization Greater than 90 Percent | Debt Instrument, Borrowing Base Utilization Greater than 90 Percent | Before December 1, 2014 | Before January 15, 2016 | Before August 1, 2016 |
| | | | | | | | | | | | | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | Subsidiaries [Member] | 8.125% Senior Notes due December 2019 | 5.50% Senior Notes due January 2021 | 5.50% Senior Notes due February 2022 |
| | | | | | | | | | | | | | Minimum | Maximum | LIBO rate | LIBO rate | Alternate base rate | Alternate base rate | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | Credit Facility due April 2018 | | | |
| | | | | | | | | | | | | | | | Minimum | Maximum | Minimum | Maximum | | | | Maximum | LIBO rate | Alternate base rate | | Minimum | Maximum | LIBO rate | Alternate base rate | | Minimum | Maximum | LIBO rate | Alternate base rate | | Minimum | Maximum | LIBO rate | Alternate base rate | | Minimum | LIBO rate | Alternate base rate | | | |
Long-Term Debt | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Long-term Debt | $2,329,634,000 | ' | $2,329,634,000 | ' | $2,262,976,000 | ' | $800,000,000 | $800,000,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Long-term Debt, Current Maturities | 0 | ' | 0 | ' | 0 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Unamortized Premium on 8.125% Senior Notes | ' | ' | ' | ' | ' | ' | 4,634,000 | 4,976,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Total Long-Term Debt, Net of Current Portion | 2,329,634,000 | ' | 2,329,634,000 | ' | 2,262,976,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Maximum credit amount | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 1,500,000,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Current borrowing base | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 1,350,000,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Number of times the Company may elect a redetermination of the borrowing base during any six month period | 1 | ' | 1 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Spread on variable rate, additional margin or Applicable Margin (as a percent) | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 1.50% | 2.50% | 0.50% | 1.50% | ' | ' | ' | ' | 1.50% | 0.50% | ' | ' | ' | 1.75% | 0.75% | ' | ' | ' | 2.00% | 1.00% | ' | ' | ' | 2.25% | 1.25% | ' | ' | 2.50% | 1.50% | ' | ' | ' |
Commitment fee rate (as a percent) | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 0.38% | 0.50% | ' | ' | ' | ' | ' | ' | 0.38% | ' | ' | ' | 0.38% | ' | ' | ' | ' | 0.50% | ' | ' | ' | ' | 0.50% | ' | ' | ' | ' | 0.50% | ' | ' | ' | ' | ' | ' |
Borrowing base utilization percentage | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 25.00% | ' | ' | ' | 25.00% | 50.00% | ' | ' | ' | 50.00% | 75.00% | ' | ' | ' | 75.00% | 90.00% | ' | ' | ' | 90.00% | ' | ' | ' | ' | ' |
Minimum current ratio | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 1 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Maximum ratio of total debt to EBITDAX | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 4 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Outstanding borrowings under the credit facility | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 775,000,000 | ' | ' | ' | ' | ' | ' | ' | 820,000,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Available credit | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 575,000,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Line of Credit Facility, Increase (Decrease), Net | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 45,000,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Principal amount of senior notes issued | ' | ' | ' | ' | ' | ' | 800,000,000 | ' | 650,000,000 | ' | 150,000,000 | ' | 350,000,000 | 350,000,000 | ' | ' | 400,000,000 | 400,000,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Interest rate, stated percentage | ' | ' | ' | ' | ' | ' | 8.13% | ' | ' | ' | ' | ' | 5.50% | ' | ' | ' | 5.50% | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Proceeds from Issuance of Long-term Debt | ' | ' | ' | ' | ' | 784,200,000 | ' | ' | ' | ' | ' | 343,100,000 | ' | ' | ' | 391,800,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Percentage of principal amount at which the entity issued notes | ' | ' | ' | ' | ' | ' | ' | ' | ' | 104.00% | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Maximum percentage of the aggregate principal amount entitled to be redeemed | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 35.00% | 35.00% | 35.00% |
Redemption price as a percentage of the principal amount of notes, if redeemed | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 108.13% | 105.50% | 105.50% |
Deferred Finance Costs, Noncurrent, Gross | 38,600,000 | ' | 38,600,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Debt Instrument, Redemption Price due to Change of Control as Percentage of Principal Amount | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 101.00% | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Debt Instrument, Redemption Price due to Additional Amounts Owed Related to Tax Witholdings as Percentage of Principal Amount | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | 100.00% | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Deferred Financing Costs | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Amortization of deferred financing costs | 1,600,000 | 1,000,000 | 3,100,000 | 2,100,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Interest Incurred On Long-Term Debt | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Interest expense | 31,800,000 | 22,400,000 | 63,400,000 | 43,800,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Capitalized interest costs | 7,600,000 | 7,400,000 | 16,000,000 | 15,900,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Amortization of bond premium | $172,000 | $160,000 | $341,000 | $317,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |