Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jul. 31, 2019	Apr. 30, 2019	Jul. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 66,652	$ 67,228	$ 65,445
Accumulated depreciation and amortization	$ 764,891	$ 745,761	$ 768,302
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	236,744,360	238,336,760	242,026,278
Treasury stock, shares	35,785,391	36,377,441	36,517,685