Shareholders' Equity | Company's Common Share Repurchase and Issuance Activity (Details) - $ / shares	9 Months Ended
	Oct. 31, 2019	Jan. 31, 2019
Change in Treasury Stock
Treasury stock balance at January 31, 2019	22,305,464
Shares of treasury stock repurchased	1,697,609
Treasury Stock Acquired, Average Cost Per Share	$ 98.37
Shares of Treasury Stock Reissued for Equity Incentive Plans	205,036
Treasury stock balance at October 31, 2019	23,798,037
Treasury Stock Held, Average Cost Per Share	$ 50.22	$ 46.53