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Cover Page - USD ($)
 12 Months Ended
May 31, 2020
Jun. 30, 2020
Nov. 30, 2019
Cover [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date May 31, 2020    
Document Fiscal Year Focus 2020    
Document Fiscal Period Focus FY    
Current Fiscal Year End Date --05-31    
Entity Interactive Data Current Yes    
Entity Current Reporting Status Yes    
Entity Registrant Name NEOGEN CORP    
Entity Central Index Key 0000711377    
Trading Symbol NEOG    
Entity Filer Category Large Accelerated Filer    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Small Business false    
Document Annual Report true    
Document Transition Report false    
Entity Public Float     $ 3,489,079,000
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Common Stock, Shares Outstanding   52,963,988  
Entity File Number 0-17988    
Title of 12(g) Security COMMON STOCK    
Security Exchange Name NASDAQ    
Entity Incorporation, State or Country Code MI    
Entity Tax Identification Number 38-2367843    
Entity Address, Address Line One 620 Lesher Place    
Local Phone Number 372-9200    
Entity Address, State or Province MI    
Entity Address, City or Town Lansing    
City Area Code 517    
Entity Address, Postal Zip Code 48912