Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jan. 31, 2019	Apr. 30, 2018	Jan. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 44,033	$ 81,813	$ 45,215
Accumulated depreciation and amortization	$ 800,834	$ 745,397	$ 757,809
Common stock, no par value (in usd per share)	$ 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	241,501,278	246,198,878	246,198,878
Treasury stock, shares	36,460,305	36,944,789	37,079,700