v3.8.0.1
Document and Entity Information - shares
3 Months Ended
Mar. 31, 2018
Apr. 12, 2018
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, 2018  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q1  
Amendment Flag false  
Common Stock    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   105,949,824
Class A Stock    
Entity Information [Line Items]    
Entity Common Stock, Shares Outstanding   1,911,354