Nature of operations and summary of significant accounting policies and going concern (Credit Loss) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Total			$ 46,085		$ 50,744
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at January 1, 2020	$ 2,768		2,768		1,097
Cumulative effect of accounting standard adoption				$ 154
Credit losses	1,517	$ (258)
Write-offs	0
Recoveries	0
Balance at March 31, 2020	2,768
Commodity sales
Segment Reporting Information [Line Items]
Total			19,818		30,819
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at January 1, 2020	198		198		0
Cumulative effect of accounting standard adoption				154
Credit losses	44
Write-offs	0
Recoveries	0
Balance at March 31, 2020	198
Joint interests
Segment Reporting Information [Line Items]
Accounts which have sufficient related revenue distributions payable to offset entire receivable balance			1,895
Accounts which have related revenue distributions payable but not sufficient to offset entire receivable balance			10,286
Accounts without related revenue distributions payable			4,181
Total			16,362		16,664
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at January 1, 2020	2,570		2,570		1,097
Cumulative effect of accounting standard adoption				0
Credit losses	1,473
Write-offs	0
Recoveries	0
Balance at March 31, 2020	2,570
Derivatives
Segment Reporting Information [Line Items]
Total			8,009		717
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at January 1, 2020	0		0		0
Cumulative effect of accounting standard adoption				0
Credit losses	0
Write-offs	0
Recoveries	0
Balance at March 31, 2020	0
Other
Segment Reporting Information [Line Items]
Total			1,896		2,544
Accounts Receivable, Allowance for Credit Loss [Roll Forward]
Balance at January 1, 2020	0		$ 0		$ 0
Cumulative effect of accounting standard adoption				$ 0
Credit losses	0
Write-offs	0
Recoveries	0
Balance at March 31, 2020	$ 0