Fair Value Disclosures - Narrative (Details) - USD ($)	12 Months Ended
	May. 31, 2015	May. 31, 2014	May. 31, 2013	Apr. 30, 2014
Fair Value Disclosures [Abstract]
Amortized cost basis, marketable securities	$ 16,100,000
Marketable securities		$ 0
Marketable securities purchased	179,200,000	48,500,000	$ 167,100,000
Shredding Transaction asset impairment charge	$ 0	$ 16,143,000	$ 0
Information systems assets, fair value				$ 5,400,000