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Fair Value Measurements Fair Value Measurement (Details 2) (USD $) | 9 Months Ended |  |  |  |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | --- | ---
Sep. 30, 2014 | Sep. 30, 2014 Net Profit Plan liability [Member] | Sep. 30, 2014 6.625% Senior Notes Due 2019 [Member] | Dec. 31, 2013 6.625% Senior Notes Due 2019 [Member] | Sep. 30, 2014 6.50% Senior Notes Due 2021 [Member] | Dec. 31, 2013 6.50% Senior Notes Due 2021 [Member] | Sep. 30, 2014 6.50% Senior Notes Due 2023 [Member] | Dec. 31, 2013 6.50% Senior Notes Due 2023 [Member] | Sep. 30, 2014 5.0% Senior Notes Due 2024 [Member] | Dec. 31, 2013 5.0% Senior Notes Due 2024 [Member]
Liabiliity measured at fair value using Level 3 inputs |  |  |  |  |  |  |  |  |  |  |
Long-term Debt, Fair Value |  |  |  | $ 364,000,000 | $ 374,290,000 | $ 371,875,000 | $ 373,625,000 | $ 415,500,000 | $ 422,000,000 | $ 492,500,000 | $ 475,315,000
Net Profits Plan |  |  |  |  |  |  |  |  |  |  |
Discount Rate Used to Calculate Currently in Payout Liabilities |  | 12.00% |  |  |  |  |  |  |  |  |
Period Used for Price Assumptions of Strip Prices of Liabilities |  | 1 |  |  |  |  |  |  |  |  |
Percent Change in Commodity Prices for Sensitivity Analysis |  | 5.00% |  |  |  |  |  |  |  |  |
Sensitivity Analysis Change in Liability, Due to Change in Commodity Prices |  | 4,000,000 |  |  |  |  |  |  |  |  |
Percent Change in Discount Rate for Sensitivity Analysis |  | 1.00% |  |  |  |  |  |  |  |  |
Sensitivity Analysis Decrease in Liability Due to Change in Discount Rate |  | 2,000,000 |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract] |  |  |  |  |  |  |  |  |  |  |
Beginning balance |  | 56,985,000 |  |  |  |  |  |  |  |  |
Net increase in liability |  | 1,156,000 | [1] |  |  |  |  |  |  |  |
Net settlements |  | (16,436,000) | [1],[2] |  |  |  |  |  |  |  |
Transfers in (out) of Level 3 |  | 0 |  |  |  |  |  |  |  |  |
Ending balance |  | $ 41,705,000 |  |  |  |  |  |  |  |  |
Proved Oil and Gas Properties |  |  |  |  |  |  |  |  |  |  |
Discount Rate Used for Fair Value of Oil and Gas Properties | 12.00% |  |  |  |  |  |  |  |  |  |
Period of New York Mercantile Exchange Strip Pricing Used for Price Forecast | 5 | 5 |  |  |  |  |  |  |  |  |
[1] | Net changes in the Company’s Net Profits Plan liability are shown in the Change in Net Profits Plan liability line item of the accompanying statements of operations
[2] | Settlements represent cash payments made or accrued under the Net Profits Plan. The Company accrued or made cash payments under the Net Profits Plan of $8.3 million as a result of divestitures during the nine months ended September 30, 2014

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