Share repurchase program (Details) - $ / shares	3 Months Ended	6 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Oct. 22, 2014
Equity [Abstract]
Number of shares authorized to be repurchased			35,000,000
Shares repurchased	270,501	576,538
Shares repurchased, average price (in USD per share)	$ 184.84	$ 173.45