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