OPERATING SEGMENTS Financial Information by Geographic Region (Details) - USD ($) $ in Thousands	12 Months Ended
	Jul. 31, 2019	Jul. 31, 2018
Financial Information by Geographic Region
Sales to unaffiliated customers	$ 277,025	$ 266,000
Net Income (Loss) attributable to Oil-Dr	12,611	8,240
Identifiable assets	205,227	194,682
Domestic Operations
Financial Information by Geographic Region
Sales to unaffiliated customers	264,476	254,158
Sales or transfers between geographic areas	5,097	5,570
Income before income taxes	14,280	14,742
Net Income (Loss) attributable to Oil-Dr	12,456	8,249
Identifiable assets	195,032	185,361
Foreign subsidiaries
Financial Information by Geographic Region
Sales to unaffiliated customers	12,549	11,842
Income before income taxes	268	124
Net Income (Loss) attributable to Oil-Dr	155	(9)
Identifiable assets	$ 10,195	$ 9,321