Financial instruments - Financial assets and liabilities measured at fair value (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jun. 30, 2018
Assets:
Equity securities	$ 14,388
Equity securities		$ 2,956
Derivatives	38,484	14,110
Liabilities:
Derivatives	7,848	5,315
Quoted Prices In Active Markets (Level 1)
Assets:
Equity securities	14,388
Equity securities		2,956
Derivatives	0	0
Liabilities:
Derivatives	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Equity securities	0
Equity securities		0
Derivatives	38,484	14,110
Liabilities:
Derivatives	7,848	5,315
Significant Unobservable Inputs (Level 3)
Assets:
Equity securities	0
Equity securities		0
Derivatives	0	0
Liabilities:
Derivatives	0	0
Measured at Net Asset Value
Assets:
Investments measured at net asset value	$ 9,601	7,208
Corporate bonds
Assets:
Debt securities		5,331
Corporate bonds \| Quoted Prices In Active Markets (Level 1)
Assets:
Debt securities		5,331
Corporate bonds \| Significant Other Observable Inputs (Level 2)
Assets:
Debt securities		0
Corporate bonds \| Significant Unobservable Inputs (Level 3)
Assets:
Debt securities		0
Asset-backed and mortgage-backed securities
Assets:
Debt securities		3,911
Asset-backed and mortgage-backed securities \| Quoted Prices In Active Markets (Level 1)
Assets:
Debt securities		0
Asset-backed and mortgage-backed securities \| Significant Other Observable Inputs (Level 2)
Assets:
Debt securities		3,911
Asset-backed and mortgage-backed securities \| Significant Unobservable Inputs (Level 3)
Assets:
Debt securities		$ 0

Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount of equity securities categorized neither as held-to-maturity nor as trading.

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Fair value, after the effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and not elected to be offset.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

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