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Employee Benefit Plans - Defined Contribution Benefits (Details) - USD ($)
$ in Millions
12 Months Ended
Jan. 31, 2020
Jan. 31, 2019
Jan. 31, 2018
Defined Contribution Plan Disclosure [Line Items]      
Deferred compensation liability $ 27.6 $ 22.6  
Retirement Savings Feature      
Defined Contribution Plan Disclosure [Line Items]      
Employees contribution percentage 50.00%    
Matching cash contribution (percentage) 50.00%    
Total compensation contribution match (percentage) 3.00%    
Defined contribution plan cost $ 9.2 8.6 $ 8.2
Employee Profit Sharing and Retirement Savings Plan      
Defined Contribution Plan Disclosure [Line Items]      
Investment in company stock (percentage) 19.00%    
Defined contribution plan cost   4.9 3.9
DCRB Feature of EPSRS Plan      
Defined Contribution Plan Disclosure [Line Items]      
Defined contribution plan cost $ 7.2 $ 4.7 $ 5.2