Standardized measure of future net cash flows related to proved reserves (Details) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Standardized measure of future net cash flows related to proved reserves
Future oil and gas cash inflows	$ 14,326	$ 25,595
Future oil & gas operating expenses	(2,554)	(4,170)
Future development costs	(1,982)	(2,983)
Future tax expense	(998)	(1,666)
Future net cash flows	8,792	16,776
10% discount to reflect timing of cash flows	(2,878)	(5,998)
Future net cash flows related to proved reserves	$ 5,914	$ 10,778