Quarterly report pursuant to Section 13 or 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
 3 Months Ended 6 Months Ended
Nov. 30, 2018
USD ($)
ft²
Nov. 30, 2017
USD ($)
item
Nov. 30, 2018
USD ($)
ft²
Nov. 30, 2017
USD ($)
May 31, 2018
USD ($)
Property, Plant and Equipment [Line Items]          
Depreciation expense $ 30.2 $ 28.4   $ 56.5  
Cost of building purchased     $ 60.8 $ 95.5 [1]  
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      
Remaining balance in escrow $ 1.5   $ 1.5   $ 14.2
Multi-Building Campus [Member] | Rochester, NY [Member] | Minimum [Member]          
Property, Plant and Equipment [Line Items]          
Renovation square feet | ft² 300,000   300,000    
[1] Amounts have been adjusted to reflect the adoption of ASC Topic 606.