Quarterly report pursuant to Section 13 or 15(d)

Description of Business, Basis of Presentation, and Significant Accounting Policies (Narrative) (Details)

v3.21.1
Description of Business, Basis of Presentation, and Significant Accounting Policies (Narrative) (Details)
$ in Millions
 3 Months Ended 9 Months Ended 12 Months Ended
Feb. 28, 2021
USD ($)
item
Feb. 28, 2021
USD ($)
item
Feb. 29, 2020
USD ($)
item
Feb. 28, 2021
USD ($)
item
segment
Feb. 29, 2020
USD ($)
item
May 31, 2021
USD ($)
May 31, 2020
USD ($)
item
Accounting Policies [Line Items]              
Number of reportable segments | segment       1      
Allowance for doubtful accounts $ 20.3 $ 20.3   $ 20.3     $ 12.5
Advance collections 3.8 3.8   3.8     6.1
Maximum individual health insurance claims liability             0.3
Stock-based compensation expense   12.6 $ 12.7 38.1 $ 36.5    
Forecast [Member]              
Accounting Policies [Line Items]              
Maximum individual health insurance claims liability           $ 0.3  
Trade Receivables [Member]              
Accounting Policies [Line Items]              
Receivables 99.3 99.3   99.3     84.7
Purchased Receivables [Member]              
Accounting Policies [Line Items]              
Receivables $ 615.8 $ 615.8   $ 615.8     $ 311.9
Revenue [Member]              
Accounting Policies [Line Items]              
Number of clients creating a credit concentration | item   0 0 0 0    
Concentration percentage   10.00% 10.00% 10.00% 10.00%    
Accounts Receivable And Unbilled Receivables [Member]              
Accounting Policies [Line Items]              
Number of clients creating a credit concentration | item 1           0
Concentration percentage 13.00%           10.00%
PEO [Member]              
Accounting Policies [Line Items]              
Maximum individual workers' compensation claims liability             $ 1.0
PEO [Member] | Forecast [Member]              
Accounting Policies [Line Items]              
Maximum individual workers' compensation claims liability           $ 1.0