Revenue Recognition - Summary of net sales by geography and product line (Details) - USD ($) $ in Thousands	3 Months Ended
	Oct. 31, 2018	Oct. 31, 2017
Disaggregation of Revenue [Line Items]
Net sales	$ 225,589	$ 212,766
United States
Disaggregation of Revenue [Line Items]
Net sales	168,938	160,940
Europe/Africa/Middle East
Disaggregation of Revenue [Line Items]
Net sales	32,014	28,101
Asia/Pacific
Disaggregation of Revenue [Line Items]
Net sales	15,752	13,607
Canada
Disaggregation of Revenue [Line Items]
Net sales	7,373	8,476
Latin America/South America
Disaggregation of Revenue [Line Items]
Net sales	1,512	1,642
Capital equipment
Disaggregation of Revenue [Line Items]
Net sales	58,132	59,169
Consumables
Disaggregation of Revenue [Line Items]
Net sales	136,821	128,359
Product service
Disaggregation of Revenue [Line Items]
Net sales	29,829	24,801
All other
Disaggregation of Revenue [Line Items]
Net sales	$ 807	$ 437