Nature of operations and summary of significant accounting policies (Unevaluated Oil and Natural Gas Properties) (Details) - USD ($) $ in Thousands		Sep. 30, 2017	Mar. 21, 2017	Dec. 31, 2016
Capitalized costs of unproved properties excluded from amortization
Leasehold acreage		$ 584,765
Capitalized interest	[1]	1,239
Wells and facilities in progress of completion		13,881
Total unevaluated oil and natural gas properties excluded from amortization		$ 599,885	$ 585,574
Predecessor
Capitalized costs of unproved properties excluded from amortization
Leasehold acreage				$ 15,455
Capitalized interest	[1]			1,894
Wells and facilities in progress of completion				3,004
Total unevaluated oil and natural gas properties excluded from amortization			$ 26,039	$ 20,353

[1] As of September 30, 2017, this amount reflects the cumulative interest capitalized on the historical acquisition cost of leasehold acreage subsequent to our establishing opening balances under fresh start accounting. Interest is not capitalized on amounts related to the fair value increase to leasehold acreage as a result of applying fresh start accounting.