Financial instruments - Financial assets and liabilities measured at fair value (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021
Assets:
Equity securities	$ 19,169	$ 20,517
Derivatives	10,270	5,486
Liabilities:
Derivatives	63,395	82,134
Quoted Prices In Active Markets (Level 1)
Assets:
Equity securities	19,169	20,517
Derivatives	0	0
Liabilities:
Derivatives	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Equity securities	0	0
Derivatives	10,270	5,486
Liabilities:
Derivatives	63,395	82,134
Significant Unobservable Inputs (Level 3)
Assets:
Equity securities	0	0
Derivatives	0	0
Liabilities:
Derivatives	$ 0	$ 0