Intangible Assets (Details) (USD $)	3 Months Ended		9 Months Ended
	Feb. 28, 2014	Feb. 28, 2013	Feb. 28, 2014	Feb. 28, 2013	May 31, 2013
Intangible assets
Gross Amount	$ 104,527,000		$ 104,527,000		$ 97,501,000
Accumulated Amortization	(52,347,000)		(52,347,000)		(45,509,000)
Net Carrying	52,180,000		52,180,000		51,992,000
Amortization expense	2,400,000	2,200,000	6,700,000	5,700,000
Customer relationships
Intangible assets
Gross Amount	74,292,000		74,292,000		69,901,000
Accumulated Amortization	(32,466,000)		(32,466,000)		(27,422,000)
Net Carrying	41,826,000		41,826,000		42,479,000
Customer relationships | Minimum
Intangible assets
Useful Life			5 years
Customer relationships | Maximum
Intangible assets
Useful Life			13 years
Software/Technology
Intangible assets
Gross Amount	14,969,000		14,969,000		14,336,000
Accumulated Amortization	(8,694,000)		(8,694,000)		(7,629,000)
Net Carrying	6,275,000		6,275,000		6,707,000
Software/Technology | Minimum
Intangible assets
Useful Life			3 years
Software/Technology | Maximum
Intangible assets
Useful Life			15 years
Covenants not to compete
Intangible assets
Gross Amount	8,523,000		8,523,000		8,069,000
Accumulated Amortization	(7,724,000)		(7,724,000)		(7,523,000)
Net Carrying	799,000		799,000		546,000
Covenants not to compete | Minimum
Intangible assets
Useful Life			2 years
Covenants not to compete | Maximum
Intangible assets
Useful Life			5 years
Other
Intangible assets
Gross Amount	6,743,000		6,743,000		5,195,000
Accumulated Amortization	(3,463,000)		(3,463,000)		(2,935,000)
Net Carrying	$ 3,280,000		$ 3,280,000		$ 2,260,000
Other | Minimum
Intangible assets
Useful Life			2 years
Other | Maximum
Intangible assets
Useful Life			5 years