Acquisitions and Dispositions - Acquisition-Relate Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013
Business Acquisition [Line Items]
Adjustments to fair value of contingent consideration liabilities	$ (5,382)	$ (3,937)	$ (3,727)
Acquisition-related expense, net	(5,167)	(2,657)	(2,141)
Acquisitions in Fiscal 2015
Business Acquisition [Line Items]
Due diligence, professional fees and other transaction costs	215
Adjustments to fair value of contingent consideration liabilities	(5,382)
Acquisition-related expense, net	$ (5,167)
Acquisitions in Fiscal 2014
Business Acquisition [Line Items]
Due diligence, professional fees and other transaction costs		1,280
Adjustments to fair value of contingent consideration liabilities		(3,937)
Acquisition-related expense, net		$ (2,657)
Acquisitions in Fiscal 2013
Business Acquisition [Line Items]
Due diligence, professional fees and other transaction costs			1,586
Adjustments to fair value of contingent consideration liabilities			(3,727)
Acquisition-related expense, net			$ (2,141)