Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Accumulated other Comprehensive Income [Roll Forward]
Balance as of December 31	$ (1,096)	$ 521
Change in fair value of derivatives	(6,821)	(3,523)
Income tax effect	0	0
Other comprehensive loss before reclassifications	(6,821)	(3,523)
Oil and gas sales	3,403	(387)
Amounts reclassified from accumulated other comprehensive income (loss)	3,403	(387)
Net other comprehensive loss	(3,418)	(3,910)
Balance as of March 31	(4,514)	(3,389)
Gains and Losses on Cash Flow Hedges
Accumulated other Comprehensive Income [Roll Forward]
Balance as of December 31	(688)	521
Change in fair value of derivatives	(6,821)	(3,523)
Income tax effect	2,538	1,261
Other comprehensive loss before reclassifications	(4,283)	(2,262)
Oil and gas sales	3,403	(387)
Income tax effect	(1,266)	0
Amounts reclassified from accumulated other comprehensive income (loss)	2,137	(387)
Net other comprehensive loss	(2,146)	(2,649)
Balance as of March 31	(2,834)	(2,128)
Change in Valuation Allowance
Accumulated other Comprehensive Income [Roll Forward]
Balance as of December 31	(408)	0
Change in fair value of derivatives	0	0
Income tax effect	(2,538)	(1,261)
Other comprehensive loss before reclassifications	(2,538)	(1,261)
Oil and gas sales	0	0
Income tax effect	1,266	0
Amounts reclassified from accumulated other comprehensive income (loss)	1,266	0
Net other comprehensive loss	(1,272)	(1,261)
Balance as of March 31	$ (1,680)	$ (1,261)