Property and equipment - Midstream service assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total midstream service assets, net	$ 96,528	$ 112,697
Depletion, depreciation and amortization	215,355	217,101	$ 265,746
Midstream service assets
Property, Plant and Equipment [Line Items]
Midstream service assets	165,232	181,718
Less accumulated depreciation and impairment	(68,704)	(69,021)
Total midstream service assets, net	96,528	112,697
Retired midstream service assets	18,800
Accumulated depreciation	9,400
Loss on retirement of midstream service assets	9,400
Depletion, depreciation and amortization	$ 9,514	$ 9,838	$ 10,206
Midstream service assets | Minimum
Property, Plant and Equipment [Line Items]
Useful life	10 years
Midstream service assets | Maximum
Property, Plant and Equipment [Line Items]
Useful life	20 years