OPERATING SEGMENTS Financial Information by Geographic Region (Details) - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2018	Jul. 31, 2017
Financial Information by Geographic Region
Sales to unaffiliated customers	$ 266,000	$ 262,307
Net Income (Loss) attributable to Oil-Dr	8,240	10,792
Identifiable assets	194,682	212,575
Domestic Operations
Financial Information by Geographic Region
Sales to unaffiliated customers	254,158	249,772
Sales or transfers between geographic areas	5,570	5,842
Income before income taxes	14,742	14,524
Net Income (Loss) attributable to Oil-Dr	8,249	10,833
Identifiable assets	185,361	204,547
Foreign subsidiaries
Financial Information by Geographic Region
Sales to unaffiliated customers	11,842	12,535
Income before income taxes	124	21
Net Income (Loss) attributable to Oil-Dr	(9)	(41)
Identifiable assets	$ 9,321	$ 8,028