Annual report pursuant to Section 13 and 15(d)

Service Revenue (Narrative) (Details)

v3.19.2
Service Revenue (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
May 31, 2019
May 31, 2018
May 31, 2017
Service Revenue [Line Items]      
Direct pass-through costs for payroll wages and payroll taxes $ 14.5 $ 7.7 $ 5.7
Direct pass-through costs related to state unemployment insurance 82.3 47.5 34.0
Direct pass-through costs related to guaranteed cost benefit plans $ 451.8 $ 274.2 $ 224.8
Revenue performance obligations timing the Company defers revenue associated with these performance obligations, which exceed one year, and subsequently recognizes these as future services are provided, over approximately three to four years    
Capitalized contract cost, amortization period 8 years    
Impairment loss $ 0.0    
Minimum [Member]      
Service Revenue [Line Items]      
Revenue performance obligations timing, years 3 years    
Maximum [Member]      
Service Revenue [Line Items]      
Revenue performance obligations timing, years 4 years