Reportable Segments - Operating Segment (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Jul. 31, 2018	Apr. 30, 2018	Jan. 31, 2018	Oct. 31, 2017	Jul. 31, 2017	Apr. 30, 2017	Jan. 31, 2017	Oct. 31, 2016	Jul. 31, 2018	Jul. 31, 2017	Jul. 31, 2016
Segment Reporting Information [Line Items]
Net sales	$ 228,854	$ 217,268	$ 213,034	$ 212,766	$ 205,502	$ 192,113	$ 184,817	$ 187,725	$ 871,922	$ 770,157	$ 664,755
Income from operations:									121,664	110,410	97,251
Interest expense, net									5,289	4,303	3,320
Other income									(1,138)	(126)	0
Income before income taxes									117,513	106,233	93,931
Identifiable assets:	963,708				786,373				963,708	786,373	694,532
Capital expenditures:									37,698	27,065	18,889
Depreciation and amortization:									34,830	33,452	25,084
Operating Segment
Segment Reporting Information [Line Items]
Income from operations:									161,020	142,753	124,034
General corporate
Segment Reporting Information [Line Items]
Income from operations:									39,356	32,343	26,783
Identifiable assets:	88,101				44,537				88,101	44,537	31,629
Capital expenditures:									11,208	5,772	941
Depreciation and amortization:									733	518	268
Endoscopy
Segment Reporting Information [Line Items]
Net sales									473,937	398,773	341,752
Endoscopy | Operating Segment
Segment Reporting Information [Line Items]
Income from operations:									86,833	73,440	61,021
Identifiable assets:	490,702				368,820				490,702	368,820	347,107
Capital expenditures:									18,996	13,816	11,299
Depreciation and amortization:									19,002	18,245	14,333
Water Purification and Filtration
Segment Reporting Information [Line Items]
Net sales									211,209	196,446	177,669
Water Purification and Filtration | Operating Segment
Segment Reporting Information [Line Items]
Income from operations:									35,100	33,159	30,620
Identifiable assets:	151,460				147,477				151,460	147,477	137,731
Capital expenditures:									4,409	3,689	3,376
Depreciation and amortization:									5,628	5,706	5,441
Healthcare Disposables
Segment Reporting Information [Line Items]
Net sales									155,180	144,457	112,584
Healthcare Disposables | Operating Segment
Segment Reporting Information [Line Items]
Income from operations:									31,707	28,000	24,486
Identifiable assets:	210,831				208,328				210,831	208,328	157,918
Capital expenditures:									2,441	2,492	2,606
Depreciation and amortization:									8,756	8,556	4,361
Dialysis
Segment Reporting Information [Line Items]
Net sales									31,596	30,481	32,750
Dialysis | Operating Segment
Segment Reporting Information [Line Items]
Income from operations:									7,380	8,154	7,907
Identifiable assets:	$ 22,614				$ 17,211				22,614	17,211	20,147
Capital expenditures:									644	1,296	667
Depreciation and amortization:									$ 711	$ 427	$ 681