Consolidated Balance Sheets (Parenthetical) - $ / shares	Jul. 31, 2018	Jul. 31, 2017
Shareholders' equity:
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, shares authorized (in shares)	2,000,000	2,000,000
Preferred stock, shares issued (in shares)	0	0
Class A [Member]
Shareholders' equity:
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	6,000,000	6,000,000
Common stock, shares issued (in shares)	3,041,911	3,035,778
Treasury stock (in shares)	15,789	27,320
Class B [Member]
Shareholders' equity:
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	10,000,000	10,000,000
Common stock, shares issued (in shares)	1,351,814	1,357,947
Treasury stock (in shares)	64,801	64,801