Other Comprehensive Income (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Other comprehensive income before reclassifications:
Change in fair value of cash flow derivatives	$ (545)
Income tax effect	0
Net of tax	(545)
Amounts reclassified from accumulated other comprehensive income:
Oil and gas sales	(540)
Income tax effect	89
Net of tax	(451)
Net other comprehensive income (loss)	(996)
Gains and Losses on Cash Flow Hedges
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	278
Other comprehensive income before reclassifications:
Change in fair value of cash flow derivatives	(545)
Income tax effect	131
Net of tax	(414)
Amounts reclassified from accumulated other comprehensive income:
Oil and gas sales	(540)
Income tax effect	130
Net of tax	(410)
Net other comprehensive income (loss)	(824)
Ending balance	(546)
Change in Valuation Allowance
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	0
Other comprehensive income before reclassifications:
Change in fair value of cash flow derivatives	0
Income tax effect	(131)
Net of tax	(131)
Amounts reclassified from accumulated other comprehensive income:
Oil and gas sales	0
Income tax effect	(41)
Net of tax	(41)
Net other comprehensive income (loss)	(172)
Ending balance	(172)
Total
Accumulated other Comprehensive Income [Roll Forward]
Beginning balance	278
Amounts reclassified from accumulated other comprehensive income:
Ending balance	$ (718)