Deferred Compensation (Additional Information) (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019	Jan. 31, 2020
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Marketable securities	$ 79,700,000		$ 79,700,000		$ 69,000,000.0
Costs to obtain a contract	88,300,000		88,300,000		98,800,000
Amortization of costs to obtain a contract	23,600,000	$ 25,500,000	46,400,000	$ 50,200,000
Impairment loss			0	$ 0
Rabbi Trust
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation liability	73,700,000		73,700,000		69,000,000.0
Deferred compensation liability, current	5,500,000		5,500,000		5,300,000
Deferred compensation liability, non-current	$ 68,200,000		$ 68,200,000		$ 63,700,000