Debt (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jul. 31, 2017	Apr. 30, 2017
Senior Notes 2017 [Member]
Debt Disclosure Details [Line Items]
Prinicipal amount of debt issued	$ 250.0
Redemption date of senior notes	May 06, 2017
Amount paid to redeem senior notes	$ 256.8
Loss on extinguishment of debt	$ 5.4
Senior Notes 2027 [Member]
Debt Disclosure Details [Line Items]
Debt offering date		Apr. 06, 2017
Prinicipal amount of debt issued		$ 300.0
Net proceeds from issuance of long-term debt		$ 296.1
Interest rate on unsecured senior note debt		3.50%
Unsecured senior note debt maturity date		Apr. 06, 2027