Disaggregated Revenue (Detail) - USD ($) $ in Thousands	3 Months Ended
	Aug. 31, 2019	Aug. 31, 2018
Disaggregation of Revenue [Line Items]
Total Revenues	$ 101,424	$ 99,626
Food Safety
Disaggregation of Revenue [Line Items]
Total Revenues	51,021	52,183
Food Safety | Natural Toxins, Allergens & Drug Residues
Disaggregation of Revenue [Line Items]
Total Revenues	20,115	18,838
Food Safety | Bacterial & General Sanitation
Disaggregation of Revenue [Line Items]
Total Revenues	10,316	10,467
Food Safety | Dehydrated Culture Media & Other
Disaggregation of Revenue [Line Items]
Total Revenues	11,279	12,217
Food Safety | Rodenticides, Insecticides & Disinfectants
Disaggregation of Revenue [Line Items]
Total Revenues	5,449	6,625
Food Safety | Genomics Services
Disaggregation of Revenue [Line Items]
Total Revenues	3,862	4,036
Animal Safety
Disaggregation of Revenue [Line Items]
Total Revenues	50,403	47,443
Animal Safety | Life Sciences
Disaggregation of Revenue [Line Items]
Total Revenues	1,723	2,080
Animal Safety | Veterinary Instruments & Disposables
Disaggregation of Revenue [Line Items]
Total Revenues	11,336	10,404
Animal Safety | Animal Care & Other
Disaggregation of Revenue [Line Items]
Total Revenues	6,405	6,398
Animal Safety | Rodenticides, Insecticides & Disinfectants
Disaggregation of Revenue [Line Items]
Total Revenues	16,718	17,146
Animal Safety | Genomics Services
Disaggregation of Revenue [Line Items]
Total Revenues	$ 14,221	$ 11,415