Revenue Recognition - Summary of net sales by geography and product line (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Jul. 31, 2020	Apr. 30, 2020	Jan. 31, 2020	Oct. 31, 2019	Jul. 31, 2019	Apr. 30, 2019	Jan. 31, 2019	Oct. 31, 2018	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2018
Disaggregation of Revenue [Line Items]
Net sales	$ 233,371	$ 236,933	$ 288,498	$ 257,246	$ 239,476	$ 228,552	$ 224,538	$ 225,589	$ 1,016,048	$ 918,155	$ 871,922
Capital equipment
Disaggregation of Revenue [Line Items]
Net sales									213,723	221,668	240,153
Consumables
Disaggregation of Revenue [Line Items]
Net sales									570,710	569,412	523,073
Product service
Disaggregation of Revenue [Line Items]
Net sales									123,771	122,752	106,764
Instrument
Disaggregation of Revenue [Line Items]
Net sales									104,440	0	0
All other
Disaggregation of Revenue [Line Items]
Net sales									3,404	4,323	1,932
United States
Disaggregation of Revenue [Line Items]
Net sales									742,410	665,661	643,744
Europe/Africa/Middle East
Disaggregation of Revenue [Line Items]
Net sales									167,360	148,334	131,130
Asia/Pacific
Disaggregation of Revenue [Line Items]
Net sales									73,517	66,228	57,108
Canada
Disaggregation of Revenue [Line Items]
Net sales									27,417	32,152	33,524
Latin America/South America
Disaggregation of Revenue [Line Items]
Net sales									$ 5,344	$ 5,780	$ 6,416