Supplemental Financial Data - Oil and Gas Producing Activities (unaudited) (Details 4) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) MMcf	Dec. 31, 2017 USD ($) MMcf
Revenue:
Oil and gas sales, including commodity derivative gains and losses	$ 52,946	$ 22,439
Expenses:
Production expenses	22,226	9,589
Depletion expense	7,305	2,157
Accretion of asset retirement obligations	868	307
Total expenses	30,399	12,053
Results of operations from oil and gas producing activities	$ 22,547	$ 10,386
Depletion rate per Mcfe | MMcf	0.89	0.4