Other Comprehensive Income (Loss) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	$ (248,935)	$ (251,095)	$ (163,067)
Other comprehensive income before reclassifications:
Change in fair value of derivatives		6,654	(4,447)
Income tax effect		(708)	0
Net of tax		5,946	(4,447)
Amounts reclassified from accumulated other comprehensive income:
Oil and gas sales		(1,461)	(1,811)
Income tax effect		543	561
Net of tax		(918)	(1,250)
Net other comprehensive loss		5,028	(5,697)
Ending balance	(262,167)	(248,935)	(251,095)
Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	278	(2,983)	947
Other comprehensive income before reclassifications:
Change in fair value of derivatives	(990)	6,654	(4,447)
Income tax effect	238	(2,475)	1,654
Net of tax	(752)	4,179	(2,793)
Amounts reclassified from accumulated other comprehensive income:
Oil and gas sales	622	(1,461)	(1,811)
Income tax effect	(148)	543	674
Net of tax	474	(918)	(1,137)
Net other comprehensive loss	(278)	3,261	(3,930)
Ending balance	0	278	(2,983)
Change in Valuation Allowance
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	0	(1,767)	0
Other comprehensive income before reclassifications:
Change in fair value of derivatives		0	0
Income tax effect		1,767	(1,654)
Net of tax		1,767	(1,654)
Amounts reclassified from accumulated other comprehensive income:
Oil and gas sales		0	0
Income tax effect		0	(113)
Net of tax		0	(113)
Net other comprehensive loss		1,767	(1,767)
Ending balance		0	(1,767)
Total
Accumulated Other Comprehensive Income [Roll Forward]
Beginning balance	278	(4,750)	947
Amounts reclassified from accumulated other comprehensive income:
Ending balance	$ 0	$ 278	$ (4,750)