v2.4.0.8

Summary of Significant Accounting Policies , Cash, Cash Equivalents and Available-for-sale Investments (Details) | 12 Months Ended
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Dec. 31, 2013
Accounting Policies [Abstract] |
Short-term investments, minimum original maturity | 3 months
Short-term investments, maximum original maturity | 1 year
Long-term investments, minimum original maturity | 1 year

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- Definition Investments, Classification as Long-term, Minimum Maturity + References No definition available. + Details
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Namespace Prefix: | ftnt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Investments, Classification as Short-term, Maximum Original Maturity + References No definition available. + Details
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Namespace Prefix: | ftnt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Investments, Classification as Short-term, Minimum Original Maturity + References No definition available. + Details
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Namespace Prefix: | ftnt_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration