Financial instruments - Gain (losses) on derivative and non-derivative financial instruments (Details) - Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017
Cross-currency swap contracts
Derivative Instruments, Gain (Loss)
Derivative and non derivative instruments gain (loss) recognized in accumulated other comprehensive income (loss)	$ 5,700	$ (2,725)	$ 7,619	$ (9,298)
Foreign denominated debt
Derivative Instruments, Gain (Loss)
Derivative and non derivative instruments gain (loss) recognized in accumulated other comprehensive income (loss)	$ 7,144	$ (10,893)	$ 11,271	$ (27,727)