v3.20.1
Summary of business and significant accounting policies - Narrative (Details)
 12 Months Ended
Aug. 30, 2019
USD ($)
$ / shares
Jan. 31, 2020
USD ($)
segment
Jan. 31, 2019
USD ($)
Jan. 31, 2018
USD ($)
Feb. 01, 2019
USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Number of segments | segment   1      
Client held funds, included in corporate cash   $ 4,000,000      
Allowance for credit loss   1,200,000 $ 100,000    
Credit losses from trade receivables   1,000,000.0 200,000    
Loss on disposition of intangible assets   700,000      
Impairment of intangible assets   0 0    
Goodwill impairment   0 0    
Capitalized contract cost   21,800,000      
Amortization of capitalized contract costs   1,900,000      
Remaining performance obligation   $ 3,700,000 400,000    
Deferred revenue recognition term   12 months      
Deferred revenue interchange arrangement recognition term   5 years      
Revenue recognized   $ 400,000      
Acquisition costs   40,810,000 2,121,000    
Operating lease liabilities   80,418,000      
Operating lease right-of-use assets   $ 83,178,000      
Acquired HSA Intangible Assets          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Useful life of intangible assets   15 years      
HSA Member          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Capitalized contract cost, amortization period   15 years      
RA Customer Relationship          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Capitalized contract cost, amortization period   7 years      
Other Expense          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Acquisition costs   $ 40,800,000 $ 2,100,000 $ 2,200,000  
Accounting Standards Update 2016-02          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Operating lease liabilities         $ 40,600,000
Operating lease right-of-use assets   $ 38,000,000.0      
Passive custodial funds          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Minimum net worth above custodial assets   2.00%      
Non-passive custodial fund          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Minimum net worth above custodial assets   4.00%      
Minimum | Leasehold improvements          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Useful life of property, plant and equipment (in years)   3 years      
Maximum | Leasehold improvements          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Useful life of property, plant and equipment (in years)   5 years      
WageWorks, Inc.          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Merger related costs, price per share | $ / shares $ 51.35        
Aggregate fair value of WageWorks stock acquired $ 2,000,000,000.0 $ 2,122,100,000      
Client-held funds, non-assets   462,000,000      
Acquisition costs   40,800,000      
WageWorks, Inc.          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Client held funds, total   682,000,000      
Client held funds, included in corporate cash   $ 220,000,000