Financial instruments - Gain (Losses) on Derivative and Non-Derivative Financial Instruments (Details) - Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Cross-currency swap contracts
Derivative Instruments, Gain (Loss)
Derivative and non derivative instruments gain (loss) recognized in accumulated other comprehensive income (loss)	$ (13,374)	$ (1,278)	$ (22,672)	$ 3,741
Foreign denominated debt
Derivative Instruments, Gain (Loss)
Derivative and non derivative instruments gain (loss) recognized in accumulated other comprehensive income (loss)	$ (15,423)	$ (11,009)	$ (43,150)	$ (11,005)