v3.5.0.2
Document and Entity Information - shares
9 Months Ended
Sep. 30, 2016
Oct. 20, 2016
Entity Information [Line Items]    
Entity Registrant Name REGENERON PHARMACEUTICALS INC  
Entity Central Index Key 0000872589  
Current Fiscal Year End Date --12-31  
Entity Filer Category Large Accelerated Filer  
Document Type 10-Q  
Document Period End Date Sep. 30, 2016  
Document Fiscal Year Focus 2016  
Document Fiscal Period Focus Q3  
Amendment Flag false  
Common Stock    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   103,558,843
Class A Stock    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   1,911,456