Document and Entity Information	3 Months Ended
	Mar. 31, 2015	Apr. 16, 2015
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, 2015
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Amendment Flag	false
Common Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		101,305,623
Class A Stock
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		1,971,868