Other Comprehensive Income (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance			$ (163,067)
Amounts reclassified from accumulated other comprehensive loss:
Ending balance	$ (236,810)		(236,810)
Gains and Losses on Cash Flow Hedges
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	(297)	$ 3,564	947	$ 5,420
Other comprehensive income before reclassifications:
Change in fair value of derivatives	101	4,077	307	7,523
Income tax effect	(37)	(1,517)	(114)	(2,799)
Net of tax	64	2,560	193	4,724
Amounts reclassified from accumulated other comprehensive loss:
Oil and gas sales	144	(4,093)	(2,043)	(10,494)
Income tax effect	(54)	1,523	760	3,904
Net of tax	90	(2,570)	(1,283)	(6,590)
Net other comprehensive income (loss)	154	(10)	(1,090)	(1,866)
Ending balance	(143)	$ 3,554	(143)	$ 3,554
Change in Valuation Allowance
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	(176)		0
Other comprehensive income before reclassifications:
Change in fair value of derivatives	0		0
Income tax effect	91		(85)
Net of tax	91		(85)
Amounts reclassified from accumulated other comprehensive loss:
Oil and gas sales	0		0
Income tax effect	0		0
Net of tax	0		0
Net other comprehensive income (loss)	91		(85)
Ending balance	(85)		(85)
Total
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	(473)		947
Other comprehensive income before reclassifications:
Change in fair value of derivatives	101		307
Income tax effect	54		(199)
Net of tax	155		108
Amounts reclassified from accumulated other comprehensive loss:
Oil and gas sales	144		(2,043)
Income tax effect	(54)		760
Net of tax	90		(1,283)
Net other comprehensive income (loss)	245		(1,175)
Ending balance	$ (228)		$ (228)