Revenue Recognition (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Natural gas sales	$ 16,018	$ 15,298
Natural gas liquids sales	1,143
Oil sales	30,891	4,213
Total natural gas, natural gas liquids, and oil revenue	48,052	19,511
Appalachia and Illinois Basin [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Natural gas sales	14,768	15,298
Natural gas liquids sales
Oil sales	4,963	4,213
Total natural gas, natural gas liquids, and oil revenue	19,731	19,511
Ventura Basin [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Natural gas sales	1,250
Natural gas liquids sales	1,143
Oil sales	25,928
Total natural gas, natural gas liquids, and oil revenue	$ 28,321