Deferred Compensation - Additional Information (Detail) - USD ($)	12 Months Ended
	Jan. 31, 2020	Jan. 31, 2019
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Marketable securities	$ 69,000,000.0
Costs to obtain a contract	98,800,000	$ 93,000,000.0
Amortization of costs to obtain a contract	101,600,000	108,800,000
Contract cost impairment loss	0	0
Rabbi Trust
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred compensation liability, current and non-current	69,000,000.0	60,300,000
Deferred compensation liability, current	5,300,000	5,000,000.0
Deferred compensation liability, non-current	$ 63,700,000	$ 55,300,000