| Condensed Consolidated Statements Of Income (USD $) In Thousands, except Per Share data, unless otherwise specified | 3 Months Ended | 6 Months Ended | ||
|---|---|---|---|---|
| Jun. 30, 2013 | Jun. 30, 2012 | Jun. 30, 2013 | Jun. 30, 2012 | |
| Revenues | $ 235,383 | $ 215,513 | $ 494,605 | $ 451,399 | 
| Operating costs and expenses: | ||||
| Lease operating expenses | 68,248 | 60,276 | 127,590 | 116,938 | 
| Production taxes | 1,780 | 1,335 | 3,569 | 2,821 | 
| Gathering and transportation | 4,608 | 4,110 | 9,052 | 8,330 | 
| Depreciation, depletion, amortization and accretion | 99,896 | 85,941 | 208,767 | 174,432 | 
| General and administrative expenses | 19,868 | 14,623 | 40,955 | 44,102 | 
| Derivative gain | (12,840) | (49,872) | (9,473) | (10,238) | 
| Total costs and expenses | 181,560 | 116,413 | 380,460 | 336,385 | 
| Operating income | 53,823 | 99,100 | 114,145 | 115,014 | 
| Interest expense: | ||||
| Incurred | 21,536 | 14,706 | 42,770 | 28,612 | 
| Capitalized | (2,532) | (3,326) | (4,964) | (6,517) | 
| Income before income tax expense | 34,819 | 87,720 | 76,339 | 92,919 | 
| Income tax expense | 12,423 | 34,153 | 27,325 | 36,134 | 
| Net income | $ 22,396 | $ 53,567 | $ 49,014 | $ 56,785 | 
| Basic and diluted earnings per common share | $ 0.29 | $ 0.70 | $ 0.64 | $ 0.75 | 
| Dividends declared per common share | $ 0.09 | $ 0.08 | $ 0.17 | $ 0.16 | 
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- Definition Aggregate dividends declared during the period for each share of common stock outstanding. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Total costs of sales and operating expenses for the period. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Details 
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- Definition The aggregate net amount of depreciation, amortization, and accretion recognized during an accounting period. As a noncash item, the net amount is added back to net income when calculating cash provided by or used in operations using the indirect method. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The amount of net income or loss for the period per each share in instances when basic and diluted earnings per share are the same amount and reported as a single line item on the face of the financial statements. Basic earnings per share is the amount of net income or loss for the period per each share of common stock or unit outstanding during the reporting period. Diluted earnings per share includes the amount of net income or loss for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period. No definition available. 
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- Definition Aggregate net gain (loss) on all derivative instruments recognized in earnings during the period, before tax effects. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Cost incurred related to the gas activities, such as transportation, marketing and processing crude oil, natural gas and refined petroleum products. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The aggregate total of expenses of managing and administering the affairs of an entity, including affiliates of the reporting entity, which are not directly or indirectly associated with the manufacture, sale or creation of a product or product line. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition This element represents the income or loss from continuing operations attributable to the economic entity which may also be defined as revenue less expenses from ongoing operations, after income or loss from equity method investments, but before income taxes, extraordinary items, and noncontrolling interest. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The sum of the current income tax expense or benefit and the deferred income tax expense or benefit pertaining to continuing operations. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition Amount of interest costs capitalized disclosed as an adjusting item to interest costs incurred. No definition available. 
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- Definition Total interest costs incurred during the period and either capitalized or charged against earnings. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Details 
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- Definition Lease expense related to property used in oil and gas production. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The portion of profit or loss for the period, net of income taxes, which is attributable to the parent. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition The net result for the period of deducting operating expenses from operating revenues. No definition available. 
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- Definition A tax assessed on oil and gas production. No definition available. 
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- Definition Aggregate revenue recognized during the period (derived from goods sold, services rendered, insurance premiums, or other activities that constitute an entity's earning process). For financial services companies, also includes investment and interest income, and sales and trading gains. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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