Description of Business and Significant Accounting Policies (Details Textual) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Feb. 29, 2012	Feb. 28, 2011	Feb. 29, 2012	Feb. 28, 2011	May 31, 2012	May 31, 2011
Description of Business and Significant Accounting Policies (Textual) [Abstract]
Direct costs billed and incurred	$ 863.9	$ 1,100.0	$ 2,600.0	$ 3,000.0
Maximum individual workers' compensation claims liability					1.0	1.0
Workers' compensation insurance costs in current liabilities	6.6		6.6			7.3
Workers' compensation insurance costs in long-term liabilities	17.9		17.9			20.6
Stock-based compensation costs recognized	$ 5.7	$ 5.3	$ 17.6	$ 18.8