Operating Segments - Concentration Risk (Details) - customer	6 Months Ended
	Jan. 31, 2016	Jan. 31, 2015
Concentration risk
Number of customers that each account for 10% or more of the consolidated net sales of the company	0	0
Segment sales | Customer concentration | Water Purification and Filtration
Concentration risk
Number of customers accounting for a percentage of segment net sales	2
Segment sales | Customer concentration | Water Purification and Filtration | Two customers
Concentration risk
Concentration risk within segment (as a percent)	43.20%
Segment sales | Customer concentration | Healthcare Disposables | Four customers
Concentration risk
Number of customers accounting for a percentage of segment net sales	4
Concentration risk within segment (as a percent)	51.00%
Net sales | Customer concentration | Dialysis | Two customers
Concentration risk
Number of customers accounting for a percentage of segment net sales	2
Concentration risk within segment (as a percent)	42.90%