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Collaboration Agreements (Bristol-Myers Squibb Collaboration) (Details) - Collaborative Arrangement, 2 BMS Compound Utilized [Member] [Member] | 3 Months Ended
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Mar. 31, 2017
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] |
Share in costs, percentage | 33.33%
BMS [Member] |
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items] |
Share in costs, percentage | 66.67%

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- Definition Collaborative Arrangement, Share in Costs, Percentage + References No definition available. + Details
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Namespace Prefix: | exel_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- 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. + References No definition available. + Details
Name: | us-gaap_CollaborativeArrangementsAndNoncollaborativeArrangementTransactionsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_TypeOfArrangementAxis=exel_CollaborativeArrangementwithTwoBristolMyersSquibbCompoundUtilizedMemberMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | dei_LegalEntityAxis=exel_BristolMyersSquibbMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |