Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance			$ (163,067)
Amounts reclassified from accumulated other comprehensive income:
Ending balance	$ (224,602)		(224,602)
Gains and Losses on Cash Flow Hedges
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	802	$ 7,018	947	$ 5,420
Other comprehensive income before reclassifications:
Change in fair value of derivatives	(595)	(1,471)	206	3,446
Income tax effect	221	547	(77)	(1,282)
Net of tax	(374)	(924)	129	2,164
Amounts reclassified from accumulated other comprehensive income:
Oil and gas sales	(1,155)	(4,029)	(2,187)	(6,401)
Income tax effect	430	1,499	814	2,381
Net of tax	(725)	(2,530)	(1,373)	(4,020)
Net other comprehensive income (loss)	(1,099)	(3,454)	(1,244)	(1,856)
Ending balance	(297)	$ 3,564	(297)	$ 3,564
Change in Valuation Allowance
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	0		0
Other comprehensive income before reclassifications:
Change in fair value of derivatives	0		0
Income tax effect	(176)		(176)
Net of tax	(176)		(176)
Amounts reclassified from accumulated other comprehensive income:
Oil and gas sales	0		0
Income tax effect	0		0
Net of tax	0		0
Net other comprehensive income (loss)	(176)		(176)
Ending balance	(176)		(176)
Total
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	802		947
Other comprehensive income before reclassifications:
Change in fair value of derivatives	(595)		206
Income tax effect	45		(253)
Net of tax	(550)		(47)
Amounts reclassified from accumulated other comprehensive income:
Oil and gas sales	(1,155)		(2,187)
Income tax effect	430		814
Net of tax	(725)		(1,373)
Net other comprehensive income (loss)	(1,275)		(1,420)
Ending balance	$ (473)		$ (473)