Description of Business, Basis of Presentation, and Significant Accounting Policies (Details) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Aug. 31, 2016 USD ($) segment $ / shares	Aug. 31, 2015 USD ($)	May 31, 2016 USD ($)
Accounting Policies [Line Items]
State of incorporation	Delaware
Number of reportable segments | segment	1
Allowance for doubtful accounts	$ 4.7		$ 4.2
Accounts receivable, net of allowance for doubtful accounts	485.6		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	9.1	$ 8.8
Excess tax benefit in income tax expense	$ 13.2
Diluted earnings per share increase | $ / shares	$ 0.035
Trade Receivables [Member]
Accounting Policies [Line Items]
Accounts receivable, net of allowance for doubtful accounts	$ 280.2		221.6
Purchased Receivables [Member]
Accounting Policies [Line Items]
Accounts receivable, net of allowance for doubtful accounts	$ 205.4		$ 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%