Operating Segments (Details) (USD $)	3 Months Ended
	Oct. 31, 2013	Oct. 31, 2012
Concentration risk
Consolidated net sales	$ 118,272,000	$ 99,681,000
Water Purification and Filtration
Concentration risk
Consolidated net sales	39,750,000	33,161,000
Dialysis
Concentration risk
Consolidated net sales	7,309,000	8,187,000
Healthcare Disposables
Concentration risk
Consolidated net sales	26,249,000	19,955,000
Segment sales | Customer concentration | Water Purification and Filtration | DaVita
Concentration risk
Concentration risk (as a percent)	23.10%
Segment sales | Customer concentration | Water Purification and Filtration | Another large dialysis provider
Concentration risk
Concentration risk (as a percent)	23.80%
Segment sales | Customer concentration | Dialysis | DaVita
Concentration risk
Concentration risk (as a percent)	38.50%
Segment sales | Customer concentration | Healthcare Disposables | Four customers
Concentration risk
Number of customers concentration risk	4
Concentration risk (as a percent)	55.60%
Net sales | Customer concentration | DaVita
Concentration risk
Concentration risk (as a percent)	10.10%	10.40%
Consolidated net sales	$ 11,988,000	$ 10,360,000
Net sales | Customer concentration | DaVita and another large dialysis provider
Concentration risk
Number of customers concentration risk	2
Concentration risk (as a percent)	18.10%
Net sales | Customer concentration | Four customers
Concentration risk
Concentration risk (as a percent)	12.30%