Name:	regn_EquitySecurityFairValueDisclosure
Namespace Prefix:	regn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. This item represents available-for-sale securities which consist of investments in mortgage-backed securities neither classified as trading or held-to-maturity securities.

No definition available.

Name:	regn_MortgageBackedSecuritiesFairValueDisclosure
Namespace Prefix:	regn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. This item represents available-for-sale securities which consist of investments in municipal bonds neither classified as trading or held-to-maturity securities.

No definition available.

Name:	regn_MunicipalBondsFairValueDisclosure
Namespace Prefix:	regn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Disclosure of the number of marketable securities held as of the reporting date.

No definition available.

Name:	regn_NumberOfMarketableSecuritiesHeld
Namespace Prefix:	regn_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. This item represents available-for-sale securities which consist of investments in U.S. government guaranteed collateralized mortgage obligations neither classified as trading or held-to-maturity securities.

No definition available.

Name:	regn_USGovernmentGuaranteedCollateralizedMortgageObligationsFairValueDisclosure
Namespace Prefix:	regn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. This item represents available-for-sale securities which consist of investments in U.S. government guaranteed corporate bonds neither classified as trading or held-to-maturity securities.

No definition available.

Name:	regn_USGovernmentGuaranteedCorporateBondsFairValueDisclosure
Namespace Prefix:	regn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. This item represents available-for-sale securities which consist of investments in U.S. government obligations neither classified as trading or held-to-maturity securities.

No definition available.

Name:	regn_USGovernmentObligationsFairValueDisclosure
Namespace Prefix:	regn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AvailableForSaleSecuritiesAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item represents Available-for-sale Securities which consist of all investments in certain debt and equity securities neither classified as trading or held-to-maturity securities. A debt security represents a creditor relationship with an enterprise. Debt securities include, among other items, US Treasury securities, US government securities, municipal securities, corporate bonds, convertible debt, commercial paper, and all securitized debt instruments. An equity security represents an ownership interest in an enterprise or the right to acquire or dispose of an ownership interest in an enterprise at fixed or determinable prices. Equity securities include, among other things, common stock, certain preferred stock, warrant rights, call options, and put options, but do not include convertible debt. An entity may opt to provide the reader with additional narrative text to better understand the nature of investments in debt and equity securities which are categorized as Available-for-sale.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

-Paragraph 12

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6379932&loc=d3e22054-111558

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Available-for-Sale Securities

-URI http://asc.fasb.org/extlink&oid=6505594