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Leases - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions | 3 Months Ended
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Mar. 31, 2020 | Mar. 31, 2019
Cash paid for amounts included in the measurement of lease liabilities |  |
Operating cash flows used for operating leases | $ 4.6 | $ 4.6
Lease liabilities arising from obtaining right-of-use assets |  |
Operating leases | $ 2.4 | $ 3.5

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- Definition Cash Flow, Lessee [Abstract] + References No definition available. + Details
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- Definition Lease Liabilities Arising from Obtaining Right-of-Use Assets [Abstract] + References No definition available. + Details
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- Definition Lease Liability Arising from Obtaining Right-of-Use Asset + References No definition available. + Details
Name: | ftnt_LeaseLiabilityArisingfromObtainingRightofUseAsset
Namespace Prefix: | ftnt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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- Definition Amount of cash outflow from operating lease, excluding payments to bring another asset to condition and location necessary for its intended use. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 45 -Paragraph 5 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918643-209977 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 20 -Section 50 -Paragraph 4 -Subparagraph (g)(1) -URI http://asc.fasb.org/extlink&oid=77888426&loc=SL77918686-209980 + Details
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