Document and Entity Information	3 Months Ended
	Mar. 31, 2013	Apr. 17, 2013 Common Stock	Apr. 17, 2013 Class A Stock
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, 2013
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		95,908,088	2,058,057