Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	May 31, 2018	May 31, 2017
Statement of Financial Position [Abstract]
Allowance on accounts receivable	$ 33,510	$ 20,525
Preferred stock, shares authorized (in shares)	100,000	100,000
Preferred stock, shares outstanding ( in shares)	0	0
Common stock, shares authorized (in shares)	425,000,000	425,000,000
Common stock, shares issued (in shares)	182,723,471	180,992,605
Common stock, shares outstanding (in shares)	106,326,383	105,400,629
Treasury stock, shares (in shares)	76,397,088	75,591,976