Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance			$ (251,095)
Other comprehensive income before reclassifications:
Change in fair value of derivatives	$ 591	$ 101	5,636	$ 307
Income tax effect	(220)	54	(329)	(199)
Net of tax	371	155	5,307	108
Amounts reclassified from accumulated other comprehensive loss:
Oil and gas sales	(618)	144	(404)	(2,043)
Income tax effect	230	(54)	150	760
Net of tax	(388)	90	(254)	(1,283)
Net other comprehensive income (loss)	(17)	245	5,053	(1,175)
Ending balance	(256,204)		(256,204)
Gains and Losses on Cash Flow Hedges
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	320	(297)	(2,983)	947
Other comprehensive income before reclassifications:
Change in fair value of derivatives	591	101	5,636	307
Income tax effect	(220)	(37)	(2,096)	(114)
Net of tax	371	64	3,540	193
Amounts reclassified from accumulated other comprehensive loss:
Oil and gas sales	(618)	144	(404)	(2,043)
Income tax effect	230	(54)	150	760
Net of tax	(388)	90	(254)	(1,283)
Net other comprehensive income (loss)	(17)	154	3,286	(1,090)
Ending balance	303	(143)	303	(143)
Change in Valuation Allowance
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	0	(176)	(1,767)	0
Other comprehensive income before reclassifications:
Change in fair value of derivatives		0		0
Income tax effect		91	1,767	(85)
Net of tax	0	91	1,767	(85)
Amounts reclassified from accumulated other comprehensive loss:
Oil and gas sales	0	0	0	0
Income tax effect	0	0	0	0
Net of tax	0	0	0	0
Net other comprehensive income (loss)	0	91	1,767	(85)
Ending balance	0	(85)	0	(85)
Total
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	320	(473)	(4,750)	947
Amounts reclassified from accumulated other comprehensive loss:
Ending balance	$ 303	$ (228)	$ 303	$ (228)