Annual report pursuant to Section 13 and 15(d)

Summarized Quarterly Financial Information (unaudited) (Schedule of Quarterly Financial Information) (Details)

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Summarized Quarterly Financial Information (unaudited) (Schedule of Quarterly Financial Information) (Details) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 12 Months Ended
Dec. 31, 2015
Sep. 30, 2015
Jun. 30, 2015
Mar. 31, 2015
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Summarized Quarterly Financial Information [Abstract]                      
Total revenues $ 33,563 $ 34,316 $ 39,242 $ 30,391 $ 38,418 $ 39,657 $ 40,502 $ 33,285 $ 137,512 $ 151,862 $ 102,569
Income (loss) from operations (118,542) [1] (83,910) [1] 6,231 [1] (12,889) [1] 7,983 11,562 12,080 6,645 (209,110) 38,270 10,664
Net income (loss) (113,170) [1] (111,805) [1] (4,967) [1] (10,197) [1] 18,962 12,201 4,740 1,863 (240,139) 37,766 4,304
Income (loss) available to common shares $ (115,144) $ (113,779) $ (6,940) $ (12,171) $ 16,988 $ 10,227 $ 2,767 $ (111) $ (248,034) $ 29,871 $ (323)
Basic income (loss) per share $ (1.58) $ (1.72) $ (0.11) $ (0.21) $ 0.31 $ 0.24 $ 0.07 $ 0.00 $ (3.77) $ 0.67 $ (0.01)
Diluted income (loss) per share $ (1.58) $ (1.72) $ (0.11) $ (0.21) $ 0.30 $ 0.23 $ 0.07 $ 0.00 $ (3.77) $ 0.65 $ (0.01)
Write-down of oil and natural gas properties $ 121,134 $ 87,301             $ 208,435    
[1] Loss from operations and net loss for the three months ended September 30, 2015 and December 31, 2015 included write-downs of oil and gas properties of $87,301 and $121,134, respectively.