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Supplemental Financial Data (Unaudited) (Details) (USD $) Share data in Thousands, except Per Share data, unless otherwise specified | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2011 | Sep. 30, 2011 | Jun. 30, 2011 | Mar. 31, 2011 | Dec. 31, 2010 | Sep. 30, 2010 | Jun. 30, 2010 | Mar. 31, 2010 | Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Selected Quarterly Financial Information |  |  |  |  |  |  |  |  |  |  |
Total revenues | $ 90,681,000 | $ 103,164,000 | $ 96,532,000 | $ 84,852,000 | $ 77,543,000 | $ 80,752,000 | $ 79,588,000 | $ 63,519,000 | $ 377,683,000 | $ 301,401,000 | $ 256,084,000
Depreciation, depletion and amortization | 13,542,000 | 19,819,000 | 17,435,000 | 14,322,000 |  |  |  |  | 65,118,000 | 56,978,000 | 60,012,000
Income from operations | (5,054,000) | (17,796,000) | 68,670,000 | 55,861,000 | 52,852,000 | 50,344,000 | 51,953,000 | 40,912,000 | 104,135,000 | 196,061,000 | 153,975,000
Net income | (19,357,000) | (30,559,000) | 56,206,000 | 45,282,000 | 42,506,000 | 40,153,000 | 41,611,000 | 30,191,000 | 54,026,000 | 154,461,000 | 114,080,000
Basic and diluted net income per limited partner unit | $ (0.18) | $ (0.28) | $ 0.52 | $ 0.42 | $ 0.39 | $ 0.51 | $ 0.38 | $ 0.24 | $ 0.50 | $ 1.54 | $ 1.17
Weighted average number of units outstanding | 106,028 | 106,028 | 106,028 | 106,028 | 106,028 | 77,896 | 74,028 | 69,451 | 106,028 | 81,917 | 67,702
Selected Quarterly Financial Information (Textuals) [Abstract] |  |  |  |  |  |  |  |  |  |  |
Asset impairments | 70,400,000 | 90,900,000 |  |  |  |  |  |  | 161,336,000 |  |
Asset impairment charges, per unit | $ 0.65 | $ 0.84 |  |  |  |  |  |  |  |  |
Deferred revenue, related to minimum royalties, recorded as revenue in a prior period |  |  |  |  |  |  |  |  | 4,000,000 |  |
Deferred revenue, related to minimum royalties, recorded as revenue in a prior period, per unit |  |  |  |  |  |  |  |  | $ 0.04 |  |
Deferred revenue, related to a prior year, non-material, recorded as revenue in a prior period | 2,500,000 | 800,000 | 700,000 |  |  |  |  |  |  |  |
Deferred revenue, related to a prior year, non-material, recorded as revenue in a prior period, per unit | $ 0.02 |  |  |  |  |  |  |  |  |  |
Increase (decrease) in Net Income |  | (2,100,000) | 3,200,000 |  |  |  |  |  |  |  |
Increase (decrease) in Net Income, per unit |  | $ (0.02) | $ 0.03 |  |  |  |  |  |  |  |
Increase (decrease) in Revenue |  | (600,000) | 5,100,000 |  |  |  |  |  |  |  |
Increase in Depletion Expense |  | 700,000 | 1,300,000 |  |  |  |  |  |  |  |
Increase (decrease) in Income (Loss) from Operations and Net income |  | $ (1,300,000) | $ 3,900,000 |  |  |  |  |  |  |  |

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