Information as to Operating Segments and Foreign and Domestic Operations - Operating Segment (Details) - USD ($)	3 Months Ended								12 Months Ended
	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2015	Apr. 30, 2015	Jan. 31, 2015	Oct. 31, 2014	Jul. 31, 2016	Jul. 31, 2015	Jul. 31, 2014
Information as to operating segments
Net sales	$ 179,002,000	$ 173,703,000	$ 158,271,000	$ 153,779,000	$ 151,255,000	$ 141,508,000	$ 135,430,000	$ 136,811,000	$ 664,755,000	$ 565,004,000	$ 488,749,000
Operating income									97,251,000	80,761,000	70,928,000
Interest expense, net									(3,320,000)	(2,364,000)	(2,317,000)
Loss on sale of business										(2,206,000)
Other expense										(2,206,000)
Income before income taxes									93,931,000	76,191,000	68,611,000
Identifiable assets	694,532,000				584,031,000				694,532,000	584,031,000	536,145,000
Capital expenditures									18,889,000	12,760,000	13,541,000
Depreciation and amortization									25,084,000	23,957,000	18,886,000
Operating Segment
Information as to operating segments
Operating income									124,034,000	99,240,000	87,026,000
General corporate
Information as to operating segments
Operating income									(26,783,000)	(18,479,000)	(16,098,000)
Identifiable assets	31,629,000				35,320,000				31,629,000	35,320,000	33,190,000
Capital expenditures									941,000	234,000	558,000
Depreciation and amortization									268,000	157,000	65,000
Endoscopy
Information as to operating segments
Net sales									341,752,000	248,654,000	190,440,000
Endoscopy | Operating Segment
Information as to operating segments
Operating income									61,021,000	40,863,000	34,194,000
Identifiable assets	347,107,000				238,799,000				347,107,000	238,799,000	203,582,000
Capital expenditures									11,299,000	7,042,000	6,820,000
Depreciation and amortization									14,333,000	10,729,000	7,001,000
Water Purification and Filtration
Information as to operating segments
Net sales									177,669,000	173,834,000	159,505,000
Water Purification and Filtration | Operating Segment
Information as to operating segments
Operating income									30,620,000	30,606,000	25,750,000
Identifiable assets	137,731,000				138,069,000				137,731,000	138,069,000	126,397,000
Capital expenditures									3,376,000	2,984,000	3,318,000
Depreciation and amortization									5,441,000	5,257,000	4,416,000
Healthcare Disposables
Information as to operating segments
Net sales									112,584,000	106,920,000	101,809,000
Healthcare Disposables | Operating Segment
Information as to operating segments
Operating income									24,486,000	19,904,000	18,720,000
Identifiable assets	157,918,000				145,391,000				157,918,000	145,391,000	138,240,000
Capital expenditures									2,606,000	1,587,000	1,367,000
Depreciation and amortization									4,361,000	6,354,000	5,968,000
Dialysis
Information as to operating segments
Net sales									32,750,000	31,240,000	30,926,000
Dialysis | Operating Segment
Information as to operating segments
Operating income									7,907,000	6,749,000	7,547,000
Identifiable assets	$ 20,147,000				$ 26,452,000				20,147,000	26,452,000	25,420,000
Capital expenditures									667,000	894,000	1,444,000
Depreciation and amortization									$ 681,000	1,382,000	1,142,000
Other.
Information as to operating segments
Net sales										4,356,000	6,069,000
Other. | Operating Segment
Information as to operating segments
Operating income										1,118,000	815,000
Identifiable assets											9,316,000
Capital expenditures										19,000	34,000
Depreciation and amortization										$ 78,000	$ 294,000