Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Oct. 31, 2017	Apr. 30, 2017	Oct. 31, 2016
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 55,265	$ 55,296	$ 56,062
Allowance for loan losses	0	0	5,484
Accumulated depreciation and amortization	$ 728,811	$ 678,161	$ 647,689
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	246,198,878	246,198,878	250,578,382
Treasury stock, shares	37,130,454	39,027,573	39,085,220