Deferred Compensation (Additional Information) (Details) - USD ($)	3 Months Ended
	Apr. 30, 2020	Apr. 30, 2019	Jan. 31, 2020
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Marketable securities	$ 77,200,000		$ 69,000,000.0
Costs to obtain a contract	91,500,000		98,800,000
Amortization of costs to obtain a contract	22,800,000	$ 24,700,000
Impairment loss	0	$ 0
Rabbi Trust
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation liability	66,200,000		69,000,000.0
Deferred compensation liability, current	4,700,000		5,300,000
Deferred compensation liability, non-current	$ 61,500,000		$ 63,700,000