Nature of operations and summary of significant accounting policies (Cash and Accounts Receivable) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Mar. 21, 2017	Dec. 31, 2016	May 31, 2016
Cash and accounts receivable
Restricted cash	$ 0
Period within which joint interest accounts receivable are due	30 days
Period within which joint interest accounts receivable are past due	60 days
Components of accounts receivable
Joint interests	$ 29,032
Accrued commodity sales	26,516
Derivative settlements	157
Other	5,326
Allowance for doubtful accounts	(668)
Accounts receivable, net	60,363	$ 46,837
Predecessor
Cash and accounts receivable
Restricted cash			$ 1,400
Components of accounts receivable
Joint interests			13,818
Accrued commodity sales			31,304
Derivative settlements				$ 119,303
Other			1,657
Allowance for doubtful accounts			(553)
Accounts receivable, net		$ 46,837	$ 46,226
JP Morgan Chase Bank, N.A.
Cash and accounts receivable
Cash held	$ 26,165