Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	$ (251,095)
Other comprehensive income before reclassifications:
Change in fair value of derivatives	2,867
Income tax effect	0
Net of tax	2,867
Amounts reclassified from accumulated other comprehensive loss:
Oil and gas sales	321
Income tax effect	0
Net of tax	321
Net other comprehensive income (loss)	3,188
Ending balance	(252,361)
Gains and Losses on Cash Flow Hedges
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	(2,983)	$ 947
Other comprehensive income before reclassifications:
Change in fair value of derivatives	2,867	801
Income tax effect	(1,066)	(298)
Net of tax	1,801	503
Amounts reclassified from accumulated other comprehensive loss:
Oil and gas sales	321	(1,032)
Income tax effect	(120)	384
Net of tax	201	(648)
Net other comprehensive income (loss)	2,002	(145)
Ending balance	(981)	$ 802
Change in Valuation Allowance
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	(1,767)
Other comprehensive income before reclassifications:
Change in fair value of derivatives	0
Income tax effect	1,066
Net of tax	1,066
Amounts reclassified from accumulated other comprehensive loss:
Oil and gas sales	0
Income tax effect	120
Net of tax	120
Net other comprehensive income (loss)	1,186
Ending balance	(581)
Total
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	(4,750)
Amounts reclassified from accumulated other comprehensive loss:
Ending balance	$ (1,562)