Subsequent events (Details) - USD ($)	Aug. 15, 2020	Jul. 27, 2020	Aug. 17, 2020
Subsequent Event [Line Items]
Common stock outstanding (in shares)			47,790,146
Subsequent event
Subsequent Event [Line Items]
Proceeds from early termination of derivative contracts		$ 28,237,000
Repayments of lines of credit		$ 24,000,000
Debtor reorganization items, lenders agreed to provide revolving commitments, minimum additional cash	$ 5,000,000
Debtor reorganization items, holders of credit agreement claims term, maximum amount of severance settlement agreements	1,220,000
Debtor reorganization items, existing equityholders term, ratable share of cash to be received	$ 1,200,000
Debtor reorganization items, existing equityholders term, cash amount per share in lieu of warrants	$ 0.01508
Subsequent event | Maximum
Subsequent Event [Line Items]
Plan of reorganization, amount of prepetition obligations to be settled in cash	$ 150,000
Subsequent event | Tranche A
Subsequent Event [Line Items]
Percentage of new common equity of cashless exercise warrants to be received by existing equityholders	5.00%
Cashless exercise warrants for existing equityholders, equity value strike price	$ 300,000,000
Cashless exercise warrants for existing equityholders, period	4 years
Subsequent event | Tranche B
Subsequent Event [Line Items]
Percentage of new common equity of cashless exercise warrants to be received by existing equityholders	5.00%
Cashless exercise warrants for existing equityholders, equity value strike price	$ 350,000,000
Cashless exercise warrants for existing equityholders, period	5 years
Exit Facility | Subsequent event
Subsequent Event [Line Items]
Debtor-in-possession financing, amount	$ 300,000,000
Debtor-in-processing financing, maturity date, period	456 days
Revolving facility | Subsequent event
Subsequent Event [Line Items]
Debtor-in-processing financing, maturity date, period	40 months
Debtor-in-processing financing, initial borrowing base term, period of proved developed producing reserves	6 months
Revolving facility | Subsequent event | Minimum
Subsequent Event [Line Items]
Debtor-in-processing financing, available capacity	$ 20,000,000
Revolving facility | Subsequent event | Maximum
Subsequent Event [Line Items]
Debtor-in-processing financing, available capacity	175,000,000
2L Convertible Notes | Subsequent event
Subsequent Event [Line Items]
Liquidity benchmark to require interest paid in kind with additional principal	20,000,000
2L Convertible Notes | Senior Notes | Subsequent event
Subsequent Event [Line Items]
Debtor-in-possession financing, amount	$ 35,000,000
New Common Stock outstanding percentage	50.00%
Debtor-in-processing financing, term	52 months
Percentage of new common equity to be received in exchange for commitment	10.00%
Required put option premium in cashin lieu of new common stock	$ 2,625,000
Management Incentive Plan term, percentage of new common equity as equity based award	7.00%
Debtor reorganization items, percentage of new common equity to be received by holders of Senior Notes	100.00%
2L Convertible Notes | Senior Notes, paid in cash | Subsequent event
Subsequent Event [Line Items]
Debtor-in-possession financing, interest rate per annum	9.00%
2L Convertible Notes | Payment in Kind (PIK) Note | Subsequent event
Subsequent Event [Line Items]
Debtor-in-possession financing, interest rate per annum	13.00%