Income Taxes - Additional Information (Detail) - USD ($) $ in Millions |
3 Months Ended | |
|---|---|---|
Apr. 30, 2018 |
Apr. 30, 2017 |
|
| Income Tax Contingency [Line Items] | ||
| Effective tax rates | 3.90% | 6.20% |
| Maximum [Member] | ||
| Income Tax Contingency [Line Items] | ||
| Provisional amounts measurement period | 1 year | |
| Effect on Provision for Income Taxes [Member] | ||
| Income Tax Contingency [Line Items] | ||
| Excess tax benefits recognized | $ 9.7 | $ 13.9 |