Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Accumulated other Comprehensive Income [Roll Forward]
Balance at beginning of period	$ 5,420	$ (1,096)
Change in fair value of derivatives	4,917	(6,821)
Income tax effect	(1,829)	0
Net of tax	3,088	(6,821)
Oil and gas sales	(2,372)	3,403
Income tax effect	882	0
Net of tax	(1,490)	3,403
Net other comprehensive income	1,598	(3,418)
Balance at end of period	7,018	(4,514)
Gains and Losses on Cash Flow Hedges
Accumulated other Comprehensive Income [Roll Forward]
Balance at beginning of period	5,420	(688)
Change in fair value of derivatives	4,917	(6,821)
Income tax effect	(1,829)	2,538
Net of tax	3,088	(4,283)
Oil and gas sales	(2,372)	3,403
Income tax effect	882	(1,266)
Net of tax	(1,490)	2,137
Net other comprehensive income	1,598	(2,146)
Balance at end of period	7,018	(2,834)
Change in Valuation Allowance
Accumulated other Comprehensive Income [Roll Forward]
Balance at beginning of period	0	(408)
Change in fair value of derivatives	0	0
Income tax effect	0	(2,538)
Net of tax	0	(2,538)
Oil and gas sales	0	0
Income tax effect	0	1,266
Net of tax	0	1,266
Net other comprehensive income	0	(1,272)
Balance at end of period	$ 0	$ (1,680)