Acquisitions and Deconsolidations - Aggregate Purchase Price for Businesses Acquired (Details) - USD ($) $ in Thousands	May. 31, 2015	May. 31, 2014	May. 31, 2013
Business Acquisition [Line Items]
Net goodwill recognized	$ 1,195,612	$ 1,267,411	$ 1,517,560
Series of Business Acquisitions
Business Acquisition [Line Items]
Fair value of tangible assets acquired	177	11,415
Net goodwill recognized	8,648	13,865
Total fair value of assets acquired	19,626	32,547
Fair value of liabilities assumed (settled) and incurred	4,131	(894)
Total cash paid for acquisitions	15,495	33,441
Service Contracts | Series of Business Acquisitions
Business Acquisition [Line Items]
Fair value of intangible assets acquired	9,856	6,343
Other Intangibles | Series of Business Acquisitions
Business Acquisition [Line Items]
Fair value of intangible assets acquired	$ 945	$ 924