Financial instruments - Financial assets and liabilities measured at fair value (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018
Assets:
Equity securities	$ 22,262
Equity securities		$ 2,956
Derivatives
Liabilities:
Derivative liability	9,851	5,315
Quoted Prices In Active Markets (Level 1)
Assets:
Equity securities	22,262
Equity securities		2,956
Quoted Prices In Active Markets (Level 1) \| Derivatives
Liabilities:
Derivative liability	0	0
Significant Other Observable Inputs (Level 2)
Assets:
Equity securities	0
Equity securities		0
Significant Other Observable Inputs (Level 2) \| Derivatives
Liabilities:
Derivative liability	9,851	5,315
Significant Unobservable Inputs (Level 3)
Assets:
Equity securities	0
Equity securities		0
Significant Unobservable Inputs (Level 3) \| Derivatives
Liabilities:
Derivative liability	0	0
Measured at Net Asset Value
Assets:
Equity securities	9,914
Equity securities		7,208
Corporate bonds
Assets:
Debt securities	4,937	5,331
Corporate bonds \| Quoted Prices In Active Markets (Level 1)
Assets:
Debt securities	4,937	5,331
Corporate bonds \| Significant Other Observable Inputs (Level 2)
Assets:
Debt securities	0	0
Corporate bonds \| Significant Unobservable Inputs (Level 3)
Assets:
Debt securities	0	0
Asset-backed and mortgage-backed securities
Assets:
Debt securities	3,673	3,911
Asset-backed and mortgage-backed securities \| Quoted Prices In Active Markets (Level 1)
Assets:
Debt securities	0	0
Asset-backed and mortgage-backed securities \| Significant Other Observable Inputs (Level 2)
Assets:
Debt securities	3,673	3,911
Asset-backed and mortgage-backed securities \| Significant Unobservable Inputs (Level 3)
Assets:
Debt securities	0	0
Derivatives
Assets:
Derivative asset	16,716	14,110
Derivatives \| Quoted Prices In Active Markets (Level 1)
Assets:
Derivative asset	0	0
Derivatives \| Significant Other Observable Inputs (Level 2)
Assets:
Derivative asset	16,716	14,110
Derivatives \| Significant Unobservable Inputs (Level 3)
Assets:
Derivative asset	$ 0	$ 0

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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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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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