Financial instruments - Financial assets and liabilities measured at fair value (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Jun. 30, 2020
Assets:
Equity securities	$ 8,547	$ 7,901
Derivatives	14,980	7,561
Liabilities:
Derivatives	58,469	34,995
Quoted Prices In Active Markets (Level 1)
Assets:
Equity securities	8,547	7,901
Derivatives	0	0
Liabilities:
Derivatives	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Equity securities	0	0
Derivatives	14,980	7,561
Liabilities:
Derivatives	58,469	34,995
Significant Unobservable Inputs (Level 3)
Assets:
Equity securities	0	0
Derivatives	0	0
Liabilities:
Derivatives	$ 0	$ 0