Fair value measurements (Fair Value of Other Financial Instruments) (Details) - Significant Other Observable Inputs (Level 2) - USD ($) $ in Thousands		Dec. 31, 2017	Dec. 31, 2016
Carrying Value
Fair Value of Other Financial Instruments
New credit facility, opening balance	[1]	$ 127,100
Estimated Fair Value
Fair Value of Other Financial Instruments
New credit facility, opening balance		127,100
9.875% Senior Notes due 2020 | Carrying Value | Predecessor
Fair Value of Other Financial Instruments
Senior Notes	[1]		$ 298,000
9.875% Senior Notes due 2020 | Estimated Fair Value | Predecessor
Fair Value of Other Financial Instruments
Senior Notes			268,200
8.25% Senior Notes due 2021 | Carrying Value | Predecessor
Fair Value of Other Financial Instruments
Senior Notes	[1]		384,045
8.25% Senior Notes due 2021 | Estimated Fair Value | Predecessor
Fair Value of Other Financial Instruments
Senior Notes			344,680
7.625% Senior Notes due 2022 | Carrying Value | Predecessor
Fair Value of Other Financial Instruments
Senior Notes	[1]		525,910
7.625% Senior Notes due 2022 | Estimated Fair Value | Predecessor
Fair Value of Other Financial Instruments
Senior Notes			470,689
Secured Debt | Carrying Value
Fair Value of Other Financial Instruments
Other secured debt	[1]	9,177
Secured Debt | Carrying Value | Predecessor
Fair Value of Other Financial Instruments
Other secured debt	[1]		10,029
Secured Debt | Estimated Fair Value
Fair Value of Other Financial Instruments
Other secured debt		$ 9,177
Secured Debt | Estimated Fair Value | Predecessor
Fair Value of Other Financial Instruments
Other secured debt			$ 10,029

[1] The carrying value excludes deductions for debt issuance costs and discounts.