Revenue Recognition - Summary of net sales by geography and product line (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Apr. 30, 2019	Apr. 30, 2018	Apr. 30, 2019	Apr. 30, 2018
Disaggregation of Revenue [Line Items]
Net sales	$ 228,552	$ 217,268	$ 678,679	$ 643,068
Capital equipment
Disaggregation of Revenue [Line Items]
Net sales	51,351	58,935	166,870	177,175
Consumables
Disaggregation of Revenue [Line Items]
Net sales	144,515	130,155	417,067	385,963
Product service
Disaggregation of Revenue [Line Items]
Net sales	31,074	27,407	91,428	78,758
All other
Disaggregation of Revenue [Line Items]
Net sales	1,612	771	3,314	1,172
United States
Disaggregation of Revenue [Line Items]
Net sales	163,367	159,375	497,469	478,024
Europe/Africa/Middle East
Disaggregation of Revenue [Line Items]
Net sales	39,949	33,702	106,278	94,254
Asia/Pacific
Disaggregation of Revenue [Line Items]
Net sales	15,140	14,341	46,476	41,190
Canada
Disaggregation of Revenue [Line Items]
Net sales	8,555	7,842	24,064	24,638
Latin America/South America
Disaggregation of Revenue [Line Items]
Net sales	$ 1,541	$ 2,008	$ 4,392	$ 4,962