Operating Segments (Details) (USD $)	3 Months Ended		9 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2013	Apr. 30, 2012
Concentration risk
Consolidated net sales	$ 105,009,000	$ 97,238,000	$ 311,053,000	$ 287,797,000
Water Purification and Filtration
Concentration risk
Consolidated net sales	29,473,000	25,955,000	88,099,000	76,505,000
Dialysis
Concentration risk
Consolidated net sales	8,072,000	8,902,000	25,019,000	27,180,000
Healthcare Disposables
Concentration risk
Consolidated net sales	22,674,000	19,336,000	66,968,000	56,668,000
Segment sales | Customer concentration | Water Purification and Filtration | DaVita
Concentration risk
Concentration risk (as a percent)			26.80%
Segment sales | Customer concentration | Water Purification and Filtration | Another large dialysis provider
Concentration risk
Concentration risk (as a percent)			26.30%
Segment sales | Customer concentration | Dialysis | DaVita
Concentration risk
Concentration risk (as a percent)			36.60%
Segment sales | Customer concentration | Healthcare Disposables | Four customers
Concentration risk
Number of customers concentration risk			4
Concentration risk (as a percent)			52.80%
Net sales | Customer concentration | DaVita
Concentration risk
Concentration risk (as a percent)			10.50%
Consolidated net sales			$ 32,785,000
Net sales | Customer concentration | DaVita and another large dialysis provider
Concentration risk
Number of customers concentration risk			2
Concentration risk (as a percent)			18.00%
Net sales | Customer concentration | Four customers
Concentration risk
Concentration risk (as a percent)			11.40%