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 |