v3.3.1.900
Document and Entity Information - shares
3 Months Ended
Mar. 31, 2016
Apr. 14, 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 Mar. 31, 2016  
Document Fiscal Year Focus 2016  
Document Fiscal Period Focus Q1  
Amendment Flag false  
Common Stock    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   103,165,457
Class A Stock    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   1,913,136