Nature of operations and summary of significant accounting policies (Cash and Accounts Receivable) (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Mar. 21, 2017	Dec. 31, 2016	May 31, 2016
Cash and accounts receivable
Restricted cash	$ 0
Components of accounts receivable
Joint interests	25,868
Accrued commodity sales	33,279
Derivative settlements	3,814
Other	1,581
Allowance for doubtful accounts	(590)
Accounts receivable, net	63,952	$ 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	$ 17,956