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Summary of Significant Accounting Policies - Additional Information (Detail)
 12 Months Ended
Dec. 29, 2017
Dec. 22, 2017
Feb. 28, 2017
May 31, 2018
USD ($)
$ / shares
shares
May 31, 2017
USD ($)
$ / shares
shares
May 31, 2016
USD ($)
$ / shares
shares
May 31, 2015
USD ($)
Significant Accounting Policies [Line Items]              
Stock split ratio 1.33            
Cash and cash equivalents       $ 83,074,000 $ 77,567,000 $ 55,257,000 $ 66,061,000
Cash held at foreign subsidiaries       7,101,000 8,132,000    
Short-term domestic certificates of deposit       27,400,000      
Commercial Paper       100,336,000      
Marketable securities       127,736,000 66,068,000    
Valuation allowance for inventory       2,200,000 2,000,000    
Depreciation expense       $ 10,315,000 $ 8,783,000 $ 7,452,000  
Finite lived intangible assets, useful life       11 years 11 years    
Weighted-average fair value per share of stock options granted | $ / shares       $ 14.47 $ 11.89 $ 9.83  
Percentage of customer credits for sales returns, pricing and other disputes, and other related matters against net revenue       3.00% 3.00% 3.00%  
Cost of goods and services sold       $ 212,000,000 $ 189,626,000 $ 168,211,000  
Unremitted earnings of foreign subsidiaries       $ 43,784,000      
Federal corporate tax rate   35.00%   21.00%      
Deferred tax benefit       $ (6,022,000)      
Current tax expense       $ 1,223,000      
Shares excluded from computations of diluted net income per share | shares       0 0 0  
ASU No. 2016-09              
Significant Accounting Policies [Line Items]              
Increase (decrease) in income tax expense       $ 4,816,000      
Minimum              
Significant Accounting Policies [Line Items]              
Marketable securities, maturity period       91 days      
Finite lived intangible assets, useful life       5 years      
Maximum              
Significant Accounting Policies [Line Items]              
Marketable securities, maturity period       1 year      
Finite lived intangible assets, useful life       25 years      
Buildings And Improvements | Minimum              
Significant Accounting Policies [Line Items]              
Property, plant and equipment estimated useful life       7 years 7 years 7 years  
Buildings And Improvements | Maximum              
Significant Accounting Policies [Line Items]              
Property, plant and equipment estimated useful life       39 years 39 years 39 years  
Furniture, Machinery and Equipment | Minimum              
Significant Accounting Policies [Line Items]              
Property, plant and equipment estimated useful life       3 years 3 years 3 years  
Furniture, Machinery and Equipment | Maximum              
Significant Accounting Policies [Line Items]              
Property, plant and equipment estimated useful life       10 years 10 years 10 years  
Shipping and Handling              
Significant Accounting Policies [Line Items]              
Cost of goods and services sold       $ 12,147,000 $ 10,185,000 $ 9,734,000  
Advertising Cost              
Significant Accounting Policies [Line Items]              
Cost of goods and services sold       $ 1,699,000 $ 1,643,000 $ 1,463,000  
Neogen Do Brazil              
Significant Accounting Policies [Line Items]              
Percentage of ownership in subsidiaries       100.00% 90.00%    
Percentage of ownership in subsidiaries after capital contribution     100.00% 100.00% 100.00%    
Neogen Latin America              
Significant Accounting Policies [Line Items]              
Percentage of ownership in subsidiaries     10.00% 100.00% 100.00%    
Customer one              
Significant Accounting Policies [Line Items]              
Account receivable percentage from major customer       10.00% 10.00%