Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Oct. 31, 2018	Apr. 30, 2018	Oct. 31, 2017
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 65,409	$ 81,813	$ 55,265
Accumulated depreciation and amortization	$ 787,978	$ 745,397	$ 728,811
Common stock, no par value	$ 0	$ 0	$ 0
Common stock, stated value per share	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized	800,000,000	800,000,000	800,000,000
Common stock, shares issued	242,026,278	246,198,878	246,198,878
Treasury stock, shares	36,499,002	36,944,789	37,130,454