Financial instruments - Gain (losses) on derivative and non-derivative financial instruments recorded in accumulated other comprehensive (loss) (Details) - Designated as Hedging Instrument - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Cross-currency swap contracts
Derivative Instruments, Gain (Loss) [Line Items]
Derivative and non-derivative instruments gain (loss) recognized in accumulated other comprehensive income (loss)	$ 5,821	$ 6,748	$ 12,372	$ 14,367
Foreign denominated debt
Derivative Instruments, Gain (Loss) [Line Items]
Derivative and non-derivative instruments gain (loss) recognized in accumulated other comprehensive income (loss)	$ 9,574	$ 13,287	$ 17,898	$ 24,558