Changes in total proved undeveloped reserves (Details)	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Gas (MMCF)
Proved undeveloped reserves - Gas	2,168	2,168	2,168
Revaluation of undeveloped reserves - Gas	0	0	0
Conversion to proved developed reserves - Gas	0	0	0
Oil (MBBLS)
Proved undeveloped reserves - Oil	68	0	68
Revaluation of undeveloped reserves - Oil	0	68	(68)
Conversion to proved developed reserves - Oil	0	0	0