Nature of operations and summary of significant accounting policies and going concern (Cash and Cash Equivalents and Accounts Receivable) (Details) $ in Thousands	6 Months Ended
Jun. 30, 2020 USD ($) segment	Dec. 31, 2019 USD ($)
Segment Reporting Information [Line Items]
Cash held	$ 55,445
Number of portfolio segments \| segment	4
Components of accounts receivable
Accounts receivable, gross	$ 43,197	$ 50,744
Allowance for credit losses	(4,215)	(1,097)
Accounts receivable, net	38,982	49,647
Joint interests
Components of accounts receivable
Accounts receivable, gross	9,992	16,664
Allowance for credit losses	(4,002)	(1,097)
Commodity sales
Components of accounts receivable
Accounts receivable, gross	14,416	30,819
Allowance for credit losses	$ (213)	0
Commodity sales \| Customer Concentration Risk \| Sales
Components of accounts receivable
Concentration risk, percentage	75.00%
Commodity sales \| Credit evaluations \| Sales
Components of accounts receivable
Concentration risk, percentage	80.00%
Derivative settlements
Components of accounts receivable
Accounts receivable, gross	$ 15,540	717
Allowance for credit losses	0	0
Other
Components of accounts receivable
Accounts receivable, gross	3,249	2,544
Allowance for credit losses	$ 0	$ 0

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