Common Stock (Details) - USD ($) $ / shares in Units, shares in Millions		3 Months Ended
	Apr. 30, 2015	Jul. 31, 2015	Sep. 02, 2015	Sep. 05, 2012
Share repurchase program approved September 5, 2012
Equity, Class of Treasury Stock [Line Items]
Share repurchase program authorized amount				$ 50,000,000
Shares repurchased, retired, and returned to an authorized by unissued status during the period		0.4
Average price of common shares repurchased (in usd per share)		$ 32.46
Shares repurchased, retired, and returned to an authorized by unissued status during the period, value	$ 2,100,000	$ 12,100,000
Subsequent Event | Share repurchase program approved September 2, 2015
Equity, Class of Treasury Stock [Line Items]
Share repurchase program authorized amount			$ 200,000,000