Variable Interest Entities and Equity Method Investment, Variable Interest Entities (Details) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 26, 2019 USD ($) Subsidiary	Jan. 27, 2018 USD ($)	Jan. 26, 2019 USD ($) Subsidiary	Jan. 27, 2018 USD ($)	Jul. 31, 2018 USD ($) Subsidiary
Variable Interest Entity [Abstract]
Current assets	$ 42,641		$ 42,641		$ 43,590
Total assets	51,529		51,529		52,829
Current liabilities	15,576		15,576		16,328
Total Ecology and Environment Inc. shareholder's equity	35,435		35,435		35,783
Noncontrolling interests shareholders' equity	484		484		664
Total shareholders' equity	35,919		35,919		36,447
Total liabilities and shareholders' equity	$ 51,529		$ 51,529		$ 52,829
Number of majority owned subsidiaries | Subsidiary	1		1		1
Total gross revenue of consolidated variable interest entities	$ 20,252	$ 21,289	$ 42,004	$ 47,394
Variable Interest Entity [Member]
Variable Interest Entity [Abstract]
Current assets	2,525		2,525		$ 2,359
Noncurrent assets	696		696		878
Total assets	3,221		3,221		3,237
Current liabilities	5,168		5,168		5,408
Noncurrent liabilities	23		23		32
Total liabilities	5,191		5,191		5,440
Total Ecology and Environment Inc. shareholder's equity	(864)		(864)		(1,051)
Noncontrolling interests shareholders' equity	(1,106)		(1,106)		(1,152)
Total shareholders' equity	(1,970)		(1,970)		(2,203)
Total liabilities and shareholders' equity	3,221		3,221		3,237
Total gross revenue of consolidated variable interest entities			5,000	$ 4,600
Restricted cash	$ 300		$ 300		$ 300