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Quarterly Financial Data - Unaudited (Results of Operations) (Details) (USD $) | 3 Months Ended | 12 Months Ended
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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
Quarterly Financial Data - Unaudited [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Revenues | $ 116,876,000 | $ 87,596,000 | $ 67,206,000 | $ 58,744,000 | $ 49,147,000 |  | $ 32,978,000 |  | $ 26,734,000 |  | $ 20,068,000 |  |  |  |
Operating income (loss) | 54,336,000 | 40,273,000 | 32,414,000 | 25,544,000 | 12,993,000 |  | 10,831,000 |  | 648,000 |  | (2,479,000) |  | 152,567,000 | 21,993,000 | (9,555,000)
Net income (loss) | (13,401,000) | 66,289,000 | 33,349,000 | (6,847,000) | 1,587,000 | [1] | (1,701,000) | [1] | (26,350,000) | [1] | (3,231,000) | [1] |  |  |
Estimated net deferred tax expense |  |  |  |  |  |  |  |  | 29,200,000 |  |  |  |  |  |
Additional discrete deferred tax expense |  |  |  |  |  |  | $ 6,200,000 |  |  |  |  |  |  |  |
[1] | In connection with the closing of the Company's IPO, it merged into a corporation and became subject to federal and state entity-level taxation. At June 30, 2010, the Company recorded an estimated net deferred tax expense of $29.2 million to recognize a deferred tax liability for the initial book and tax basis differences. At September 30, 2010, the Company recorded an additional $6.2 million discrete deferred tax expense for changes in estimates on its initial deferred tax liability recorded in June. See Note 11.

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