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Summary of Significant Accounting Policies - Additional Information (Detail)			1 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 22, 2017	Dec. 29, 2017	May 31, 2019 USD ($) $ / shares shares	May 31, 2018 USD ($) $ / shares shares	May 31, 2017 USD ($) $ / shares shares	Feb. 28, 2017	May 31, 2016 USD ($)
Significant Accounting Policies [Line Items]
Stock split ratio			1.33
Marketable securities, maturity period				2 years
Finite lived intangible assets, useful life				10 years	11 years
Federal corporate tax rate		35.00%		21.00%	21.00%
Commercial Paper				$ 208,155,000
Short-term domestic certificates of deposit				17,681,000
Marketable securities				225,836,000	$ 127,736,000
Valuation allowance for inventory				2,250,000	2,200,000
Depreciation expense				11,315,000	10,315,000	$ 8,783,000
Cost of goods and services sold				222,266,000	$ 211,658,000	$ 189,353,000
Unremitted earnings of foreign subsidiaries				$ 55,553,000
Weighted-average fair value per share of stock options granted | $ / shares				$ 14.91	$ 14.47	$ 11.89
Cash held at foreign subsidiaries				$ 8,711,000	$ 7,101,000
Cash and cash equivalents				$ 41,688,000	$ 83,074,000	$ 77,567,000		$ 55,257,000
Shares excluded from computations of diluted net income per share | shares				0	0	0
Shipping and Handling
Significant Accounting Policies [Line Items]
Cost of goods and services sold				$ 13,503,000	$ 12,147,000	$ 10,185,000
Advertising Cost
Significant Accounting Policies [Line Items]
Cost of goods and services sold				$ 1,471,000	$ 1,411,000	$ 1,426,000
Customer One
Significant Accounting Policies [Line Items]
Account receivable percentage from major customer				10.00%	10.00%
Neogen Do Brazil
Significant Accounting Policies [Line Items]
Percentage of ownership in subsidiaries							10.00%
Latin America
Significant Accounting Policies [Line Items]
Percentage of ownership in subsidiaries				100.00%	100.00%
Percentage of ownership in subsidiaries before capital contribution	90.00%
Percentage of ownership in subsidiaries Before capital contribution	100.00%
Minimum
Significant Accounting Policies [Line Items]
Marketable securities, maturity period				91 days
Finite lived intangible assets, useful life				5 years
Minimum | Buildings And Improvements
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life				7 years	7 years	7 years
Minimum | Furniture, fixtures, machinery and equipment
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life				3 years
Maximum
Significant Accounting Policies [Line Items]
Finite lived intangible assets, useful life				25 years
Maximum | Buildings And Improvements
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life				39 years	39 years	39 years
Maximum | Furniture, fixtures, machinery and equipment
Significant Accounting Policies [Line Items]
Property, Plant and Equipment, Useful Life				10 years

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