Annual report pursuant to Section 13 and 15(d)

Property and Equipment, Net of Accumulated Depreciation (Narrative) (Details)

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Property and Equipment, Net of Accumulated Depreciation (Narrative) (Details)
$ in Millions
 1 Months Ended 3 Months Ended 12 Months Ended
Sep. 30, 2017
Nov. 30, 2017
USD ($)
May 31, 2018
USD ($)
May 31, 2017
USD ($)
May 31, 2016
USD ($)
Aug. 31, 2017
ft²
item
Property, Plant and Equipment [Line Items]            
Depreciation expense     $ 116.9 $ 108.8 $ 99.2  
Cost of building purchased     154.0 $ 94.3 $ 97.7  
Multi-Building Campus [Member] | Rochester, NY [Member]            
Property, Plant and Equipment [Line Items]            
Number of buildings purchased | item           5
Cost of building purchased   $ 34.7        
Construction in progress     32.0      
Escrow for building renovations   $ 16.0 $ 14.2      
Multi-Building Campus [Member] | Rochester, NY [Member] | Minimum [Member]            
Property, Plant and Equipment [Line Items]            
Renovation square feet | ft²           300,000
Multi-Building Campus [Member] | Rochester, NY [Member] | County Of Monroe Industrial Development Agency [Member]            
Property, Plant and Equipment [Line Items]            
Public benefits and inducements expiration date Dec. 31, 2039