Shareholders' Equity | Company's Common Share Repurchase and Issuance Activity (Details) - $ / shares |
3 Months Ended | |
|---|---|---|
Apr. 30, 2018 |
Jan. 31, 2018 |
|
| Increase (Decrease) in Treasury Stock | ||
| Treasury stock balance at January 31, 2018 | 21,083,972 | |
| Shares repurchased | 0 | |
| Treasury stock balance at April 30, 2018 | 20,927,954 | |
| Treasury Stock Held, Average Cost Per Share | $ 44.59 | $ 44.59 |
| Equity Incentive Plans | ||
| Increase (Decrease) in Treasury Stock | ||
| Shares of treasury stock reissued for equity incentive plans | 156,018 |