Nature of operations and summary of significant accounting policies and going concern (Revenue Recognition) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Gross commodity sales	$ 19,966	$ 72,491	$ 75,329	$ 125,716
Transportation and processing	(4,086)	(5,784)	(10,598)	(10,390)
Net commodity sales	15,880	66,707	64,731	115,326
Oil
Disaggregation of Revenue [Line Items]
Gross commodity sales	10,384	50,990	47,410	83,792
Natural gas
Disaggregation of Revenue [Line Items]
Gross commodity sales	5,679	10,476	14,334	21,682
Natural gas liquids
Disaggregation of Revenue [Line Items]
Gross commodity sales	$ 3,903	$ 11,025	$ 13,585	$ 20,242