Information as to Operating Segments and Foreign and Domestic Operations (Details) (USD $)	3 Months Ended								12 Months Ended
	Jul. 31, 2013	Apr. 30, 2013	Jan. 31, 2013	Oct. 31, 2012	Jul. 31, 2012	Apr. 30, 2012	Jan. 31, 2012	Oct. 31, 2011	Jul. 31, 2013	Jul. 31, 2012	Jul. 31, 2011
Concentration risk
Consolidated net sales	$ 113,973,000	$ 105,009,000	$ 106,363,000	$ 99,681,000	$ 98,693,000	$ 97,238,000	$ 97,297,000	$ 93,262,000	$ 425,026,000	$ 386,490,000	$ 321,651,000
Water Purification and Filtration
Concentration risk
Consolidated net sales									134,196,000	114,609,000	104,308,000
Dialysis
Concentration risk
Consolidated net sales									33,148,000	35,644,000	38,055,000
Healthcare Disposables
Concentration risk
Consolidated net sales									90,904,000	76,229,000	70,202,000
Segment sales | Customer concentration | Water Purification and Filtration | DaVita
Concentration risk
Concentration risk (as a percent)									23.90%
Segment sales | Customer concentration | Water Purification and Filtration | Another large dialysis provider
Concentration risk
Concentration risk (as a percent)									24.60%
Segment sales | Customer concentration | Dialysis | DaVita
Concentration risk
Concentration risk (as a percent)									36.40%
Segment sales | Customer concentration | Healthcare Disposables | Four customers
Concentration risk
Number of customers concentration risk									4
Concentration risk (as a percent)									54.00%
Net sales | Customer concentration | DaVita
Concentration risk
Concentration risk (as a percent)									10.40%	10.20%
Consolidated net sales									$ 44,204,000	$ 39,300,000
Net sales | Customer concentration | DaVita and another large dialysis provider
Concentration risk
Number of customers concentration risk									2
Concentration risk (as a percent)									18.20%
Net sales | Customer concentration | Four customers
Concentration risk
Concentration risk (as a percent)									11.60%