v2.4.1.9

Accumulated Other Comprehensive Income (Loss) (Changes in Accumulated Balances of Other Comprehensive Income (Loss)) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ (349)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1
Other comprehensive income before reclassifications	578us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax
Amounts reclassified from accumulated other comprehensive income (loss)	(3)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax
Net current-period other comprehensive income	575us-gaap_OtherComprehensiveIncomeLossBeforeTax
Ending balance	226us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1
Tax Benefit (Provision) Related to Items of Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	191ftnt_AccumulatedOtherComprehensiveIncomeLossTax
Other comprehensive income before reclassifications	(311)ftnt_OtherComprehensiveIncomeLossbeforeReclassificationsTax
Amounts reclassified from accumulated other comprehensive income (loss)	1ftnt_ReclassificationfromAccumulatedOtherComprehensiveIncomeCurrentPeriodTax
Net current-period other comprehensive income	(310)us-gaap_OtherComprehensiveIncomeLossTax
Ending balance	(119)ftnt_AccumulatedOtherComprehensiveIncomeLossTax
Unrealized Gains and Losses on Investments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(540)us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember
Other comprehensive income before reclassifications	889us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsBeforeTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember
Amounts reclassified from accumulated other comprehensive income (loss)	(4)us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember
Net current-period other comprehensive income	885us-gaap_OtherComprehensiveIncomeLossBeforeTax / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember
Ending balance	$ 345us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1 / us-gaap_StatementEquityComponentsAxis = us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember

X

- Definition

Accumulated Other Comprehensive Income Loss Tax

+ References

No definition available.

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- Definition

Other Comprehensive Income (Loss) before Reclassifications, Tax

+ References

No definition available.

+ Details

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- Definition

Reclassification from Accumulated Other Comprehensive Income, Current Period, Tax

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No definition available.

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- Definition

Amount before tax of increase (decrease) in accumulated in equity from transactions and other events and circumstances from non-owner sources. Excludes net income (loss), and accumulated changes in equity from transactions resulting from investments by owners (distributions to owners).

+ References

No definition available.

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- Definition

Amount before tax and reclassification adjustments of other comprehensive income (loss).

+ References

No definition available.

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- Definition

Amount before tax, after reclassification adjustments of other comprehensive income (loss).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 1A

-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669619-108580



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669625-108580



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 45

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=35755396&loc=d3e33775-111570

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- Definition

Amount of tax expense (benefit) allocated to other comprehensive income (loss).

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 31

-Article 5



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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3



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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 20

-Section 45

-Paragraph 11

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=18498875&loc=d3e39076-109324



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 220

-SubTopic 10

-Section 45

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e640-108580

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- Definition

Amount before tax of reclassification adjustments of other comprehensive income (loss).

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No definition available.

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