Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Apr. 30, 2021	Jul. 31, 2020
Allowance for doubtful accounts	$ 6,230	$ 6,085
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Common Class A [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	35,000,000	35,000,000
Common stock, shares issued	3,272,000	3,272,000
Common stock, shares outstanding	1,574,000	1,574,000
Treasury stock, shares	1,698,000	1,698,000
Common Class B [Member]
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	26,343,000	25,961,000
Common stock, shares outstanding	24,151,000	24,345,000
Treasury stock, shares	2,192,000	1,616,000