v2.4.1.9

Investments in Privately-Held Companies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015 privately_held_company
Investments, All Other Investments [Abstract]
Investments in equity securities of privately-held companies	$ 6.4us-gaap_CostMethodInvestmentsOriginalCost
Number of privately-held companies	3ftnt_NumberofPrivatelyHeldCompanies

X

- Definition

Number of Privately Held Companies

+ References

No definition available.

+ Details

Name:	ftnt_NumberofPrivatelyHeldCompanies
Namespace Prefix:	ftnt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Original amount of cost-method investments at the acquisition date.

+ References

No definition available.

+ Details

Name:	us-gaap_CostMethodInvestmentsOriginalCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

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