Revenue Recognition - Summary of net sales by geography and product line (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Disaggregation of Revenue [Line Items]
Net sales	$ 224,538	$ 213,034	$ 450,127	$ 425,800
United States
Disaggregation of Revenue [Line Items]
Net sales	165,164	157,708	334,102	318,648
Europe/Africa/Middle East
Disaggregation of Revenue [Line Items]
Net sales	34,319	32,498	66,333	60,553
Asia/Pacific
Disaggregation of Revenue [Line Items]
Net sales	15,568	12,987	31,320	26,849
Canada
Disaggregation of Revenue [Line Items]
Net sales	8,138	8,318	15,509	16,796
Latin America/South America
Disaggregation of Revenue [Line Items]
Net sales	1,349	1,523	2,863	2,954
Capital equipment
Disaggregation of Revenue [Line Items]
Net sales	57,387	59,071	115,519	118,240
Consumables
Disaggregation of Revenue [Line Items]
Net sales	135,731	127,413	272,552	255,807
Product service
Disaggregation of Revenue [Line Items]
Net sales	30,525	$ 26,550	60,354	51,351
All other
Disaggregation of Revenue [Line Items]
Net sales	$ 895		$ 1,702	$ 402