Quarterly report [Sections 13 or 15(d)]

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

v3.26.3
Description of Business, Basis of Presentation, and Significant Accounting Policies (Narrative) (Details)
$ in Millions
 3 Months Ended 12 Months Ended
Aug. 31, 2026
USD ($)
Segment
Item
Aug. 31, 2025
USD ($)
Item
May 31, 2027
USD ($)
May 31, 2026
USD ($)
Item
Accounting Policies [Line Items]        
Number of reportable segments | Segment 1      
Workers' Compensation Liability, Current $ 88.8     $ 80.7
Workers' Compensation Liability, Noncurrent 160.5     157.0
Advance collections 3.1     1.1
Maximum individual health insurance claims liability       0.5
PEO accrued health insurance and dental and vision plan reserves in current liabilities 67.0     $ 64.3
Stock-based compensation costs recognized $ 19.3 $ 26.8    
Change in accounting principle, accounting standards update, adoption date Jun. 01, 2026      
Change in accounting principle, accounting standards update, adopted [true false] true      
Change in accounting principle, accounting standards update, immaterial effect [true false] true      
Accounting Standards Update [Extensible Enumeration] us-gaap:AccountingStandardsUpdate202505Member      
Forecast [Member]        
Accounting Policies [Line Items]        
Maximum individual health insurance claims liability     $ 0.5  
Accounts And Unbilled Receivables [Member]        
Accounting Policies [Line Items]        
Number of clients creating a credit concentration | Item 0     0
Revenue [Member]        
Accounting Policies [Line Items]        
Number of clients creating a credit concentration | Item 0 0    
PEO Aggregate Claims Exceeding $1.0M [Member] | Minimum [Member]        
Accounting Policies [Line Items]        
Maximum individual workers' compensation claims liability       $ 1.0
Individual workers' compensation claims liability       1.0
PEO Aggregate Claims Exceeding $1.0M [Member] | Maximum [Member]        
Accounting Policies [Line Items]        
Maximum individual workers' compensation claims liability       $ 1.0
PEO Aggregate Claims Exceeding $1.0M [Member] | Maximum [Member] | Forecast [Member]        
Accounting Policies [Line Items]        
Maximum individual workers' compensation claims liability     $ 1.0