Financial instruments - Gain (Losses) on Derivative Financial Instruments (Details) - Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Cross-currency swap contracts
Derivative Instruments, Gain (Loss)
Derivative and non derivative instruments gain (loss) recognized in accumulated oher comprehensive income (loss)	$ (1,278)	$ 10,934	$ 3,741	$ 3,140
Foreign denominated debt
Derivative Instruments, Gain (Loss)
Derivative and non derivative instruments gain (loss) recognized in accumulated oher comprehensive income (loss)	$ (11,009)	$ (2,131)	$ (11,005)	$ 2,202