Quarterly report pursuant to Section 13 or 15(d)

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

v3.7.0.1
Description of Business, Basis of Presentation, and Significant Accounting Policies (Narrative) (Details)
$ / shares in Units, $ in Millions
3 Months Ended 9 Months Ended 12 Months Ended
Feb. 28, 2017
USD ($)
Feb. 29, 2016
USD ($)
Feb. 28, 2017
USD ($)
segment
$ / shares
Feb. 29, 2016
USD ($)
May 31, 2016
USD ($)
Accounting Policies [Line Items]          
State of incorporation     Delaware    
Number of reportable segments | segment     1    
Allowance for doubtful accounts $ 5.3   $ 5.3   $ 4.2
Accounts receivable, net of allowance for doubtful accounts 429.9   429.9   408.6
Maximum individual workers' compensation claims liability     1.3   1.3
Maximum individual health insurance claims liability     0.3   0.3
Stock-based compensation costs recognized 8.9 $ 8.6 26.5 $ 26.1  
Excess tax benefit in income tax expense     $ 17.3    
Diluted earnings per share increase | $ / shares     $ 0.05    
Trade Receivables [Member]          
Accounting Policies [Line Items]          
Accounts receivable, net of allowance for doubtful accounts 212.5   $ 212.5   221.6
Purchased Receivables [Member]          
Accounting Policies [Line Items]          
Accounts receivable, net of allowance for doubtful accounts $ 217.4   $ 217.4   $ 187.0
Germany [Member] | Total Revenue [Member] | Geographic Concentration Risk [Member]          
Accounting Policies [Line Items]          
Percentage of total revenue less than one percent     1.00% 1.00%