Segment Information and Geographic Data (Detail) - USD ($) $ in Thousands		3 Months Ended
		Aug. 31, 2019	Aug. 31, 2018	May 31, 2019
Segment Reporting Information [Line Items]
Product revenues to external customers		$ 101,424	$ 99,626
Operating income (loss)		16,264	16,479
Total assets		721,144	640,926	$ 695,740
Operating Segments | Food Safety
Segment Reporting Information [Line Items]
Product revenues to external customers		51,021	52,183
Operating income (loss)		9,134	10,873
Total assets		207,725	201,727
Operating Segments | Animal Safety
Segment Reporting Information [Line Items]
Product revenues to external customers		50,403	47,443
Operating income (loss)		8,300	6,706
Total assets		222,403	212,786
Product Revenues
Segment Reporting Information [Line Items]
Product revenues to external customers		81,948	82,960
Product Revenues | Operating Segments | Food Safety
Segment Reporting Information [Line Items]
Product revenues to external customers		45,877	46,933
Product Revenues | Operating Segments | Animal Safety
Segment Reporting Information [Line Items]
Product revenues to external customers		36,071	36,027
Service Revenues
Segment Reporting Information [Line Items]
Product revenues to external customers		19,476	16,666
Service Revenues | Operating Segments | Food Safety
Segment Reporting Information [Line Items]
Product revenues to external customers		5,144	5,250
Service Revenues | Operating Segments | Animal Safety
Segment Reporting Information [Line Items]
Product revenues to external customers		14,332	11,416
Corporate and Eliminations | Operating Segments
Segment Reporting Information [Line Items]
Operating income (loss)	[1]	(1,170)	(1,100)
Total assets	[1]	$ 291,016	$ 226,413

[1] Includes corporate assets, consisting principally of cash and cash equivalents, marketable securities, current and deferred tax accounts and overhead expenses not allocated to specific business segments. Also includes the elimination of intersegment transactions.