Gas Reserves - Investment - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Reserve Quantities [Line Items]
Gas reserves	$ 8,444	$ 11,409	$ 13,646
Gas reserves, non-current	178,863	175,898	173,661
Less: Accumulated amortization	149,011	141,414	132,202
Total gas reserves	38,296	45,893	55,105
Less: Deferred taxes on gas reserves	8,760	10,572	13,324
Net investment in gas reserves	29,536	35,321	41,781
Jonah Energy LLC
Reserve Quantities [Line Items]
Total Gas Reserves Investment	$ 2,700	$ 3,000	$ 3,400