Share repurchase program (Details) (USD $)	3 Months Ended	6 Months Ended
	Dec. 31, 2012	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased (in shares)	7,500,000	7,500,000
Authorization to repurchase common shares, percentage of shares of common stock outstanding at the end of the prior fiscal year	5.00%
Share repurchased (in shares)	613,785	1,931,762
Average price per share repurchased, including commissions (in usd per share)	$ 81.46	$ 81.36
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock Repurchase Program, Number of Shares Authorized to be Repurchased (in shares)	7,500,000	7,500,000