Annual report pursuant to Section 13 and 15(d)

Acquisitions and Dispositions (Unaudited Pro Forma Financial Information) (Details)

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Acquisitions and Dispositions (Unaudited Pro Forma Financial Information) (Details) - Central Midland Basin Texas [Member] - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Business Acquisition [Line Items]    
Revenues $ 180,458 $ 151,766
Income from operations 53,526 36,002
Income available to common stockholders $ 33,674 $ 4,033
Basic $ 0.57 $ 0.07
Diluted $ 0.56 $ 0.07