Collaboration Agreements - Sanofi, Antibody Narrative (Details) - USD ($)		3 Months Ended
Apr. 01, 2020	Mar. 31, 2020
Sanofi Collaboration Agreement, Antibody
Disaggregation of Revenue [Line Items]
Percentage of Trial Costs borne by collaborating party		80.00%
Percentage of Trial Costs borne by entity		20.00%
Maximum amount of sales milestone payments if total sales achieve specific levels		$ 250,000,000.0
Levels of twelve month sales at which sales milestone payments would be received		$ 1,000,000,000.0
Period for achieving sales target for milestone payment, rolling basis		12 months
Praluent Agreement
Disaggregation of Revenue [Line Items]
Percentage of damages company is responsible for		50.00%
Subsequent Event \| Praluent Agreement
Disaggregation of Revenue [Line Items]
Royalty percentage to be received on net product sales outside of the United States	5.00%
Sanofi \| Praluent Agreement
Disaggregation of Revenue [Line Items]
Percentage of royalty payment that can be used to offset litigation proceedings		50.00%

Aggregate amount of twelve month sales upon which sales milestone would be received.

No definition available.

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- Definition

Loss Contingency, Percentage Of Damages Responsible For

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No definition available.

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- Definition

The maximum amount of sales milestone payments the Company is eligible to receive when and if total annual sales achieve certain specified levels.

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No definition available.

+ Details

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- Definition

Percentage Of Royalty Payment That Can Be Offset

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No definition available.

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Namespace Prefix:	regn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of subsequent Shared Phase 3 Trial costs borne by the collaborating party upon receipt of the first positive Phase 3 trial results for a co-developed drug candidate.

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No definition available.

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The percentage of subsequent Shared Phase 3 Trial costs borne by the Company upon receipt of the first positive Phase 3 trial results for a co-developed drug candidate.

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No definition available.

+ Details

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Namespace Prefix:	regn_
Data Type:	num:percentItemType
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Period Type:	duration

- Definition

Period for Achieving Sales Target for Milestone Payment, Rolling Basis

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No definition available.

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Namespace Prefix:	regn_
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Balance Type:	na
Period Type:	duration

- Definition

Royalty Percentage To Be Received On Net Product Sales Outside Of United States

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No definition available.

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Namespace Prefix:	regn_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

+ Details

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- Details

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- Details

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- Details

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- Details

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