Nature of operations and summary of significant accounting policies (Cash and Accounts Receivable) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Components of accounts receivable
Joint interests	$ 28,867	$ 29,032
Accrued commodity sales	34,381	26,516
Derivative settlements	0	157
Other	3,338	5,326
Allowance for doubtful accounts	(806)	(668)
Accounts receivable, net	65,780	$ 60,363
JP Morgan Chase Bank, N.A.
Cash and accounts receivable
Cash held	$ 46,640

Accrued oil and natural gas sales receivable.

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- Definition

Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]

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Derivative settlements receivable.

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- Definition

A valuation allowance for trade and other receivables due to an Entity within one year (or the normal operating cycle, whichever is longer) that are expected to be uncollectible.

+ References

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This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties.

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- Definition

Current portion of accounts receivable attributable to joint interest partners in oil and gas properties. These are billings to the non-operators associated with the operation of wells and are based on those owners' working interests in the wells. For classified balance sheets, represents the current amount receivable, that is amounts expected to be collected within one year or the normal operating cycle, if longer.

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Amount, before allowance, of receivables classified as other, due within one year or the operating cycle, if longer.

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The total amount due to the entity within one year of the balance sheet date (or one operating cycle, if longer) from outside sources, including trade accounts receivable, notes and loans receivable, as well as any other types of receivables, net of allowances established for the purpose of reducing such receivables to an amount that approximates their net realizable value.

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