Financial instruments - Gain (losses) on derivative and non-derivative financial instruments (Details) - Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended
Sep. 30, 2018	Sep. 30, 2017
Cross-currency swap contracts
Derivative Instruments, Gain (Loss)
Derivative and non derivative instruments gain (loss) recognized in accumulated other comprehensive income (loss)	$ 1,920	$ (6,574)
Foreign denominated debt
Derivative Instruments, Gain (Loss)
Derivative and non derivative instruments gain (loss) recognized in accumulated other comprehensive income (loss)	$ 4,127	$ (16,834)

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