Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jul. 31, 2019	Jul. 31, 2018
Assets
Allowance for doubtful accounts and contract adjustments	$ 1,004	$ 1,284
Property, buildings and equipment, accumulated depreciation	$ 17,066	$ 16,799
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)	3,192,990	3,041,911
Treasury stock (in shares)	64,823	15,789
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)	1,200,735	1,351,814
Treasury stock (in shares)	0	64,801