Financial instruments - Financial assets and liabilities measured at fair value (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Jun. 30, 2020
Assets:
Equity securities	$ 15,751	$ 7,901
Derivatives	18,755	7,561
Liabilities:
Derivatives	89,735	34,995
Quoted Prices In Active Markets (Level 1)
Assets:
Equity securities	15,751	7,901
Derivatives	0	0
Liabilities:
Derivatives	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Equity securities	0	0
Derivatives	18,755	7,561
Liabilities:
Derivatives	89,735	34,995
Significant Unobservable Inputs (Level 3)
Assets:
Equity securities	0	0
Derivatives	0	0
Liabilities:
Derivatives	$ 0	$ 0