Segment Information (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016
Segment Reporting Information [Line Items]
Total consolidated net sales		$ 79,071	$ 70,859	$ 155,566	$ 147,509
Total consolidated depreciation and amortization				7,048	7,024
Total consolidated operating income		9,040	6,137	17,720	13,457
Total other income (expense), net		(457)	(103)	(404)	(272)
Income before income taxes		8,583	6,034	17,316	13,185
Operating Segments
Segment Reporting Information [Line Items]
Total consolidated net sales		79,071	70,859	155,566	147,509
Total consolidated depreciation and amortization	[1]	3,496	3,479	7,048	7,024
Total consolidated operating income	[2]	9,040	6,137	17,720	13,457
Total other income (expense), net		(457)	(103)	(404)	(272)
Income before income taxes		8,583	6,034	17,316	13,185
Operating Segments | Electronic Chemicals
Segment Reporting Information [Line Items]
Total consolidated net sales		69,766	62,521	136,688	128,603
Total consolidated depreciation and amortization	[1]	2,793	2,849	5,645	5,764
Total consolidated operating income	[2]	9,583	8,470	17,644	15,744
Operating Segments | Other Chemicals
Segment Reporting Information [Line Items]
Total consolidated net sales		9,305	8,338	18,878	18,906
Total consolidated depreciation and amortization	[1]	285	286	572	583
Total consolidated operating income	[2]	3,023	2,804	6,704	6,568
Other Activities
Segment Reporting Information [Line Items]
Total consolidated depreciation and amortization	[1]	418	344	831	677
Total consolidated operating income	[2]	$ (3,566)	$ (5,137)	$ (6,628)	$ (8,855)

[1] Segment depreciation excludes depreciation for restructuring and realignment.

[2] Segment income from operations includes allocated corporate overhead expenses, but excludes restructuring and realignment charges, which are included in other activities.