Legal proceedings/contingencies and other obligations (Details) R$ in Millions, $ in Millions	1 Months Ended
	Apr. 30, 2019 USD ($)	Apr. 30, 2019 BRL (R$)	Jan. 31, 2019 USD ($)	Jan. 31, 2019 BRL (R$)	Mar. 31, 2019 USD ($)
Loss Contingencies [Line Items]
Purchase obligations					$ 41.1
SEMAG | Pending Litigation | Wastewater Discharge
Loss Contingencies [Line Items]
Proposed penalty			$ 0.5	R$ 2.0
Subsequent Event | SEMAG | Pending Litigation | Wastewater Discharge
Loss Contingencies [Line Items]
Proposed penalty	$ 0.6	R$ 2.2