Information as to Reportable Segments and Foreign and Domestic Operations - Operating Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2016	Apr. 30, 2016	Jan. 31, 2016	Oct. 31, 2015	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2015
Segment Reporting Information [Line Items]
Net sales	$ 205,502	$ 192,113	$ 184,817	$ 187,725	$ 179,002	$ 173,703	$ 158,271	$ 153,779	$ 770,157	$ 664,755	$ 565,004
Operating income:									110,410	97,251	80,761
Interest expense, net									4,303	3,320	2,364
Other income									(126)	0	0
Loss on sale of business									0	0	2,206
Income before income taxes									106,233	93,931	76,191
Identifiable assets:	786,373				694,532				786,373	694,532	584,031
Capital expenditures:									27,065	18,889	12,760
Depreciation and amortization:									33,452	25,084	23,957
Operating Segment
Segment Reporting Information [Line Items]
Operating income:									142,753	124,034	99,240
General corporate
Segment Reporting Information [Line Items]
Operating income:									32,343	26,783	18,479
Identifiable assets:	44,537				31,629				44,537	31,629	35,320
Capital expenditures:									5,772	941	234
Depreciation and amortization:									518	268	157
Endoscopy
Segment Reporting Information [Line Items]
Net sales									398,773	341,752	248,654
Endoscopy | Operating Segment
Segment Reporting Information [Line Items]
Operating income:									73,440	61,021	40,863
Identifiable assets:	368,820				347,107				368,820	347,107	238,799
Capital expenditures:									13,816	11,299	7,042
Depreciation and amortization:									18,245	14,333	10,729
Water Purification and Filtration
Segment Reporting Information [Line Items]
Net sales									196,446	177,669	173,834
Water Purification and Filtration | Operating Segment
Segment Reporting Information [Line Items]
Operating income:									33,159	30,620	30,606
Identifiable assets:	147,477				137,731				147,477	137,731	138,069
Capital expenditures:									3,689	3,376	2,984
Depreciation and amortization:									5,706	5,441	5,257
Healthcare Disposables
Segment Reporting Information [Line Items]
Net sales									144,457	112,584	106,920
Healthcare Disposables | Operating Segment
Segment Reporting Information [Line Items]
Operating income:									28,000	24,486	19,904
Identifiable assets:	208,328				157,918				208,328	157,918	145,391
Capital expenditures:									2,492	2,606	1,587
Depreciation and amortization:									8,556	4,361	6,354
Dialysis
Segment Reporting Information [Line Items]
Net sales									30,481	32,750	31,240
Dialysis | Operating Segment
Segment Reporting Information [Line Items]
Operating income:									8,154	7,907	6,749
Identifiable assets:	$ 17,211				$ 20,147				17,211	20,147	26,452
Capital expenditures:									1,296	667	894
Depreciation and amortization:									427	681	1,382
Other
Segment Reporting Information [Line Items]
Net sales									0	0	4,356
Other | Operating Segment
Segment Reporting Information [Line Items]
Operating income:									0	0	1,118
Capital expenditures:									0	0	19
Depreciation and amortization:									$ 0	$ 0	$ 78