Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jul. 31, 2017	Jul. 31, 2016
Current assets:
Contract receivables, allowance for doubtful accounts and contract adjustments	$ 2,125	$ 6,792
Property, building and equipment, accumulated depreciation	$ 16,994	$ 18,324
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)	3,035,778	3,035,778
Treasury stock (in shares)	27,320	39,272
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)	1,357,947	1,357,947
Treasury stock (in shares)	64,801	64,801