Shareholders' Equity | Company's Common Share Repurchase and Issuance Activity (Details) - $ / shares	3 Months Ended
	Apr. 30, 2020	Jan. 31, 2020
Change in Treasury Stock
Treasury stock balance at January 31, 2020	23,819,230
Shares of Treasury Stock Reissued for Equity Incentive Plans	232,030
Treasury stock balance at April 30, 2020	23,587,200
Treasury Stock Held, Average Cost Per Share	$ 50.30	$ 50.30