Fortinet (FTNT) 10-Q 7 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Oct. 31, 2018
DEI [Abstract]
Entity Registrant Name	FORTINET INC
Entity Central Index Key	1,262,039
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		170,370,205

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
CURRENT ASSETS:
Cash and cash equivalents	$ 1,169.3	$ 811
Short-term investments	464.9	440.3
Accounts receivable—Net	324.4	348.2
Inventory	80.8	77.3
Prepaid expenses and other current assets	38.7	40
Total current assets	2,078.1	1,716.8
LONG-TERM INVESTMENTS	38.6	98
PROPERTY AND EQUIPMENT—NET	265.4	245.4
Deferred contract costs	169.6	0
DEFERRED TAX ASSETS	147.8	146.9
OTHER INTANGIBLE ASSETS—NET	18.1	16.3
GOODWILL	25.7	14.6
OTHER ASSETS	20.2	19.9
TOTAL ASSETS	2,763.5	2,257.9
CURRENT LIABILITIES:
Accounts payable	66.6	70
Accrued liabilities	60.7	50
Accrued payroll and compensation	85.4	92
Income taxes payable	23	21.4
Deferred revenue	876.2	793.8
Total current liabilities	1,111.9	1,027.2
DEFERRED REVENUE	668.2	542.5
INCOME TAX LIABILITIES	80.7	90.2
OTHER LIABILITIES	11.1	8.6
Total liabilities	1,871.9	1,668.5
COMMITMENTS AND CONTINGENCIES (Note 10)
STOCKHOLDERS’ EQUITY:
Common stock, $0.001 par value—300 shares authorized; 170.3 and 167.9 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	0.2	0.2
Additional paid-in capital	1,048.4	909.6
Accumulated other comprehensive loss	(1)	(0.8)
Accumulated deficit	(156)	(319.6)
Total stockholders’ equity	891.6	589.4
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 2,763.5	$ 2,257.9

Consolidated Balance Sheets Par

Consolidated Balance Sheets Parenthetical - $ / shares	Sep. 30, 2018	Dec. 31, 2017
Common Stock, par value (dollars per share)	$ 0.001	$ 0.001
Common Stock, shares authorized	300,000,000	300,000,000
Common Stock, shares issued	170,300,000	167,900,000
Common Stock, shares outstanding	170,300,000	167,900,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
REVENUE:
Product	$ 164.5	$ 137.1	$ 473.6	$ 415.1
Service	289.4	237.1	820.6	663.2
Total revenue	453.9	374.2	1,294.2	1,078.3
COST OF REVENUE:
Product	72	58.1	204.1	174.2
Service	39.6	35.5	117.8	105.7
Total cost of revenue	111.6	93.6	321.9	279.9
GROSS PROFIT:
Product	92.5	79	269.5	240.9
Service	249.8	201.6	702.8	557.5
Total gross profit	342.3	280.6	972.3	798.4
OPERATING EXPENSES:
Research and development	58.7	53.5	179	155.9
Sales and marketing	198.3	172.4	576.4	509.1
General and administrative	22.5	21	71	65.5
Restructuring charges	0	0	0	0.3
Total operating expenses	279.5	246.9	826.4	730.8
OPERATING INCOME	62.8	33.7	145.9	67.6
INTEREST INCOME—NET	6.9	3.9	17.2	9.5
OTHER INCOME (EXPENSE)—NET	0.9	0.4	(4.3)	1.9
INCOME BEFORE INCOME TAXES	70.6	38	158.8	79
PROVISION FOR INCOME TAXES	11.9	11.3	9.2	18.6
NET INCOME	$ 58.7	$ 26.7	$ 149.6	$ 60.4
Net income per share (Note 9):
Basic (in dollars per share)	$ 0.35	$ 0.15	$ 0.89	$ 0.34
Diluted (in dollars per share)	$ 0.33	$ 0.15	$ 0.86	$ 0.34
Weighted-average shares outstanding:
Basic (in shares)	169.8	175.5	168.7	175.3
Diluted (in shares)	175.7	179	173.7	179

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Net income	$ 58.7	$ 26.7	$ 149.6	$ 60.4
Other comprehensive income (loss):
Change in unrealized gains (losses) on investments	0.5	0.2	(0.1)	0.5
Tax provision related to change in unrealized gains (losses) on investments	0.1	0.1	0.1	0.2
Other comprehensive income (loss)	0.4	0.1	(0.2)	0.3
Comprehensive income	$ 59.1	$ 26.8	$ 149.4	$ 60.7

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net income	$ 149.6	$ 60.4
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation	120.3	102.7
Amortization of deferred contract costs	66.3	0
Depreciation and amortization	41	41.2
Other	(1.7)	3.2
Amortization of investment premiums	0	2.1
Changes in operating assets and liabilities:
Accounts receivable—net	38	51.4
Inventory	(19)	17.7
Prepaid expenses and other current assets	1.8	(9.6)
Deferred contract costs	(98.8)	0
Deferred tax assets	(19.1)	(22.1)
Other assets	(3.3)	(0.4)
Accounts payable	(4.9)	(16.5)
Accrued liabilities	(2)	8
Accrued payroll and compensation	(8.6)	(3.5)
Other liabilities	(2.8)	(3.8)
Deferred revenue	209.9	184.4
Income taxes payable	(8)	21.7
Net cash provided by operating activities	458.7	436.9
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of investments	(405.2)	(359.6)
Sales of investments	39.6	10
Maturities of investments	405.6	329.1
Purchases of property and equipment	(41.4)	(121.6)
Payments made in connection with business combination, net of cash acquired	(6)	0
Net cash used in investing activities	(7.4)	(142.1)
CASH FLOWS FROM FINANCING ACTIVITIES:
Repurchase and retirement of common stock	(117.1)	(124)
Proceeds from issuance of common stock	81.6	61.9
Taxes paid related to net share settlement of equity awards	(48)	(35.9)
Payments of debt assumed in connection with business combination	(9.5)	0
Net cash used in financing activities	(93)	(98)
NET INCREASE IN CASH AND CASH EQUIVALENTS	358.3	196.8
CASH AND CASH EQUIVALENTS—Beginning of period	811	709
CASH AND CASH EQUIVALENTS—End of period	1,169.3	905.8
NON-CASH INVESTING AND FINANCING ACTIVITIES:
Transfers of evaluation units from inventory to property and equipment	16.2	16.3
Liability for purchase of property and equipment and asset retirement obligations	$ 6.7	$ 8.6

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Basis of Presentation and Preparation —The unaudited condensed consolidated financial statements of Fortinet, Inc. and its wholly owned subsidiaries (collectively, “we,” “us” or “our”) have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) for interim financial information, as well as the instructions to Form 10-Q pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (the “SEC”). Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements, and should be read in conjunction with our audited consolidated financial statements as of and for the year ended December 31, 2017, contained in our Annual Report on Form 10-K filed with the SEC on February 26, 2018 (the “Form 10-K”). In the opinion of management, all adjustments, which includes normal recurring adjustments, considered necessary for a fair presentation have been included. All intercompany balances, transactions and cash flows have been eliminated. The results of operations for the three and nine months ended September 30, 2018 are not necessarily indicative of the results for the full year or for any future periods. The condensed consolidated balance sheet as of December 31, 2017 is derived from the audited consolidated financial statements for the year ended December 31, 2017. The preparation of financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Actual results could differ materially from those estimates. There have been no material changes to our significant accounting policies as of and for the three and nine months ended September 30, 2018 , except for the accounting policies for revenue recognition, trade receivables and deferred contract costs that were updated as a result of adopting Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) (“Topic 606”). For more information, refer to the “Recently Adopted Accounting Standards” and Note 2. Recently Adopted Accounting Standards Financial Instruments – Recognition and Measurement In January 2016, the Financial Accounting Standard Board (“FASB”) issued ASU 2016-01—Financial Instruments—Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities, with further clarifications made recently with the issuance of ASU 2018-03, which requires most equity investments to be measured at fair value, with subsequent changes in fair value recognized in net income. A practicality exception applies to those equity investments that do not have a readily determinable fair value. These investments may be measured at cost, adjusted for changes in observable prices minus impairment. ASU 2016-01 was effective prospectively for us beginning on January 1, 2018 for our equity investments, which were previously accounted for under the cost-method. We adopted ASU 2016-01 on January 1, 2018. There was no material impact on our condensed consolidated financial statements as of the adoption date. Revenue Recognition In May 2014, the FASB issued Topic 606, which supersedes the revenue recognition requirements in Topic 605, Revenue Recognition, and requires entities to recognize revenue when control of the promised goods or services is transferred to customers at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. We adopted Topic 606 as of January 1, 2018 using the modified retrospective transition method. The comparative information has not been restated and continues to be reported under the accounting standards in effect for those periods. We recorded a net reduction to our accumulated deficit as of January 1, 2018 of $ 117.3 million due to the cumulative impact of adopting Topic 606. The primary impact of adopting Topic 606 relates to the deferral of our incremental contract costs, which are comprised of sales commissions. Prior to January 1, 2018, we expensed all sales commissions upfront. Beginning on January 1, 2018, we continue to expense sales commissions related to product sales upfront, but capitalize and then amortize certain sales commissions on service contracts over the applicable amortization period. The capitalized sales commissions for initial service contracts are deferred and then amortized as expense on a straight-line basis over the period of benefit which we have determined to be five years. Sales commissions for renewal contracts are deferred and then amortized on a straight line basis over the contractual period of the underlying contracts. The deferral of sales commissions generated a deferred tax liability of $23.8 million , of which $18.0 million was recorded against deferred tax assets and the remaining $ 5.8 million was recorded in other long-term liabilities on our condensed consolidated balance sheet. The impact on deferred revenue as of January 1, 2018 was $4.1 million , which primarily relates to certain changes in revenue recognition on software license sales and the acceleration of revenue from U.S.-based channel partners which were previously deferred until the product was sold through. Beginning on January 1, 2018, our sales returns reserve is now included on the balance sheet in accrued liabilities and no longer as a reduction to our accounts receivable. See Note 2 for further details. The cumulative effects of the changes made to our January 1, 2018 condensed consolidated balance sheet for the adoption of Topic 606 were as follows (in millions): Balance at December 31, 2017 Adjustments due to Topic 606 Balance at January 1, 2018 Assets: Accounts receivable, net $ 348.2 $ 13.6 $ 361.8 Inventory $ 77.3 $ (0.1 ) $ 77.2 Deferred tax assets $ 146.9 $ (18.0 ) $ 128.9 Deferred contract costs $ — $ 137.1 $ 137.1 Liabilities: Accrued liabilities $ 50.0 $ 13.6 $ 63.6 Deferred revenue, current $ 793.8 $ 0.3 $ 794.1 Deferred revenue, non-current $ 542.5 $ (4.4 ) $ 538.1 Other liabilities, non-current $ 8.6 $ 5.8 $ 14.4 Stockholders’ equity: Accumulated deficit $ (319.6 ) $ 117.3 $ (202.3 ) Recent Accounting Standards Not Yet Effective Leases In February 2016, the FASB issued ASU 2016-02—Leases, which requires the recognition of right-of-use assets and lease liabilities on the consolidated balance sheet for substantially all leases. ASU 2016-02 includes a number of optional practical expedients that entities may elect to apply. ASU 2016-02 will also require significant additional disclosures about the amount, timing and uncertainty of cash flows from leases. In July 2018, the FASB issued ASU 2018-10—Codification Improvements to Topic 842, Leases, and ASU 2018-11 Leases (Topic 842) Targeted Improvements, which address questions about how to apply certain aspects of Accounting Standards Codification (“ASC”) 2016-02. The clarifications address the rate implicit in the lease, impairment of the net investment in the lease, lessee reassessment of lease classification, lessor reassessment of lease term and purchase options and variable payments that depend on an index or rate, and provide an alternative transition approach that allows companies to initially apply the new leases standard by recognizing a cumulative-effect adjustment on adoption date. ASC 2016-02 will be effective for us beginning on January 1, 2019, using a modified retrospective approach. Based on our current lease portfolio, we currently estimate the value of leased assets and liabilities that may be recognized on the consolidated balance sheet to be at least $45.0 million . We are continuing to evaluate the impact of ASU 2016-02 and our estimate is subject to change. We do not believe that ASC 2016-02 will have a material impact on our consolidated statements of operations and cash flows. We expect to expand our disclosures in the notes to consolidated financial statements to include more details on our leases, significant judgments and lease-related amounts recognized in the consolidated financial statements. Stock Compensation In June 2018, the FASB issued ASU 2018-07—Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, which simplifies the accounting for share-based payments to nonemployees by aligning it with the accounting for share-based payments to employees subject to certain exceptions. ASC 2018-07 expands the scope of ASC Topic 718, Compensation-Stock Compensation (“ASC 718”) to include share-based payments granted to nonemployees in exchange for goods or services used or consumed in an entity’s own operations and supersedes the guidance in ASC 505-50 by moving it to ASC 718. This amendment is effective for us beginning January 1, 2019. Early adoption is permitted, but no earlier than an entity’s adoption date of ASC 606. We are currently evaluating the impact of ASU 2018-07 on our consolidated financial statements. Cloud Computing In August 2018, the FASB issued ASU 2018-15—Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, which requires a customer in a cloud computing arrangement that is a service contract to follow the internal-use software guidance in ASC Subtopic 350-40 to determine which implementation costs to capitalize as assets or expense as incurred. ASU 2018-15 is effective for us beginning January 1, 2020, and early adoption is permitted. We are currently evaluating the impact of ASU 2018-15 on our consolidated financial statements. Fair Value Measurements In August 2018, the FASB issued ASU 2018-13—Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which eliminates, adds and modifies certain disclosure requirements for fair value measurements in ASC 820—Fair Value Measurement as part of its disclosure framework project. ASU 2018-13 is effective for us beginning January 1, 2020. The amendments in ASU 2018-13 on changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments in ASU 2018-13 should be applied retrospectively to all periods presented upon their effective date. Early adoption is permitted upon issuance of ASU 2018-13. An entity is permitted to early adopt any removed or modified disclosures upon issuance of ASU 2018-13 and delay adoption of the additional disclosures until their effective date. We are currently evaluating the impact of ASU 2018-13 on our consolidated financial statements. Comprehensive Income In February 2018, the FASB issued ASU 2018-02—Income Statement-Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which allows companies to reclassify stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017 (the “2017 Tax Act”), from accumulated other comprehensive income to retained earnings. ASU 2018-02 also requires certain new disclosures regardless of the election. ASU 2018-02 is effective for us beginning January 1, 2019, and early adoption is permitted. We are currently evaluating the impact of ASU 2018-02 on our consolidated financial statements. Financial Instruments In June 2016, the FASB issued ASU 2016-13—Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which requires a financial asset (or a group of financial assets) measured at an amortized cost basis to be presented at the net amount expected to be collected. The new approach to estimating credit losses (referred to as the current expected credit losses model) applies to most financial assets measured at amortized cost and certain other instruments, including trade and other receivables, loans and held-to-maturity debt securities. ASU 2016-13 is effective for us beginning on January 1, 2020, and early adoption is permitted. We are currently evaluating the impact of ASU 2016-13 on our consolidated financial statements.

Revenue Recognition

Revenue Recognition	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenue Recognition	REVENUE RECOGNITION Revenue recognition On January 1, 2018 we adopted Topic 606 using the modified retrospective method applied to those contracts which were not completed as of January 1, 2018. Results for reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported under Topic 605. The details of significant changes and quantitative impact of the changes are discussed below. We derive the majority of our revenue from sales of our products, FortiGuard security subscription and FortiCare technical support services, and other services. Beginning in 2018, revenues are recognized when control of these goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. Prior to 2018, revenue was recognized under Topic 605 when all of the following criteria were met: (i) persuasive evidence of an arrangement existed, (ii) delivery has occurred or services have been rendered, (iii) sales price was fixed or determinable and (iv) collectability was reasonably assured. Under Topic 606, we determine revenue recognition through the following steps: • identification of the contract, or contracts, with the customer, • identification of the performance obligations in the contract, including evaluation of performance obligations as to being distinct goods or services in a contract, • determination of the transaction price, • allocation of the transaction price to the performance obligations in the contract, and • recognition of revenue when, or as, we satisfy a performance obligation. Product revenue primarily consists of sales of hardware and software licenses of our FortiGate and Fabric products. We derive a majority of product sales from our FortiGate products. Our FortiGate products include a broad set of built-in security and networking features and functionalities including firewall, SD-WAN, data leak prevention, VPN, switch and wireless controller and WAN acceleration, among others. We previously recognized product revenue for sales to distributors that had no general right of return and direct sales to end-customers upon shipment, based on general revenue recognition accounting guidance once all other revenue recognition criteria were met. Certain distributors are granted stock rotation rights, limited rights of return or rebates for sales of our products. The arrangement fee for this group of distributors was not fixed or determinable when products were shipped and revenue was therefore deferred and recognized upon sell-through. Under Topic 606, we recognize product revenue upon shipment when control of the promised goods is transferred to the customer. We recognize revenue from term licenses upon electronic transfer of the license key to the customer. Previously, term licenses were recognized over the license period. We generally provide a 1-year warranty on hardware products and a 90-day warranty on software that provides assurance that our hardware or software products conform to published specifications. Such assurance-type warranties are not deemed to be separate performance obligations from the hardware or software product and costs associated with providing the warranties are accrued in accordance with ASC 460-10. Service revenue relates to sales of our FortiGuard security subscription, FortiCare technical support services, and other services. Our FortiGuard security subscription services provide access to our application control, intrusion prevention, anti-botnet and mobile, anti-spam, web filtering, cloud sandbox and virus outbreak protection, industry security, security rating service and threat intelligent service functionality. Our FortiCare support services include rights to unspecified software upgrades, maintenance releases and patches, telephone and internet access to technical support personnel. Our typical subscription and contractual support term is one to three years, and to a lesser extent, five years. Our revenue recognition for service arrangements did not significantly change under Topic 606. We continue to recognize revenue from these services ratably over the contractual service period because of continuous transfer of control to the customer over the maintenance period. Revenue related to subsequent renewals of these services are recognized over the support term of the renewal agreement. We also generate a small portion of our revenue from other services consisting of professional services, training and software-as-a-service (“SaaS”) which is either hosted or cloud-based services. We recognize revenue from professional and training services as the services are provided. We recognize revenue from SaaS as the subscription service is delivered over the term, which is typically one year, or on a monthly usage basis. To date, SaaS revenue has not represented a significant percentage of our total revenue. Our sales contracts typically contain multiple deliverables, such as hardware, software license, security subscription, technical support services and other services, which are generally capable of being distinct and accounted for as separate performance obligations. We evaluated the criteria to be distinct under Topic 606 and concluded that the hardware and software license were distinct and distinct in the context of the contract from the security subscription and technical support services, as the customer can benefit from the hardware and license without the services and the services are separately identifiable within the contract. We allocate the transaction price to each performance obligation based on relative standalone selling price. We determine standalone selling price based on the historical pricing and discounting practices for those services when sold separately. We determine standalone selling price for a product or service by considering multiple historical factors including, but not limited to, cost of products, gross margin objectives, pricing practices, geographies and the term of the service contract that fall within a reasonably range as a percentage of list price. Revenue is reported net of sales tax. Under Topic 605, revenue from contracts that contain our products and services are allocated to each unit of accounting based on an estimated selling price using vendor-specific objective evidence (“VSOE”) of selling price, if it existed, or third-party evidence (“TPE”) of selling price. If neither VSOE nor TPE of selling price existed for a deliverable, we used our best estimate of selling price for that deliverable. For multiple-element arrangements where software deliverables were included, revenue was allocated to the non-software deliverables and to the software deliverables as a group using the relative estimated selling prices of each of the deliverables in the arrangement based on the estimated selling price hierarchy. The amount allocated to the software deliverables was then allocated to each software deliverable using the residual method when VSOE of fair value existed. If evidence of VSOE of fair value of one or more undelivered elements did not exist, all software allocated revenue was deferred and recognized when delivery of those elements occurred or when fair value was established. When the undelivered element for which we did not have VSOE of fair value was support, revenue for the entire arrangement was recognized ratably over the support period. The same residual method and VSOE of fair value principles applied for our multiple element arrangements that contained only software elements. In certain circumstances, our contracts include provisions for sales rebates and other customer incentive programs. Additionally, in limited circumstances, we may permit end-customers, distributors and resellers to return our products, subject to varying limitations, for a refund within a reasonably short period from the date of purchase. These amounts are accounted for as variable consideration that can decrease the transaction price. We estimate variable consideration at the most likely amounts to which we expect our customers to be entitled. We include estimated amounts in the transaction price to the extent that it is probable that a significant reversal of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is resolved. Our estimate for sales return reserve was $13.7 million as of September 30, 2018 and is included in current liabilities in our condensed consolidated balance sheet. Under Topic 605, a sales return reserve of $13.6 million was presented as a reduction to accounts receivable as of December 31, 2017. We generally invoice at the time of our sale for the total price of the hardware, software licenses, security and technical support and other services, and the invoice is payable within 30 to 45 days. We also invoice certain services on a monthly basis. Amounts billed and due from our customers are classified as receivables on the balance sheet and do not bear interest. Our deferred revenue primarily consists of amounts that have been invoiced but have not been recognized as revenue as of period end. During the three and nine months ended September 30, 2018 , we recognized $ 173.0 million and $615.3 million , respectively, in revenue that was included in the deferred revenue balance as of December 31, 2017. Shipping and handling fees charged to our customers are recognized as product revenue in the period shipped and the related costs for providing these services are recorded as a cost of sale. Shipping and handling fees recognized as product revenue were not significant during the three and nine months ended September 30, 2018 and 2017. Disaggregation of Revenue The following table presents our revenue disaggregated by major product and service lines (in millions): Three Months Ended Nine Months Ended September 30, September 30, 2017 (1) September 30, September 30, 2017 (1) Product $ 164.5 $ 137.1 $ 473.6 $ 415.1 Service: Security subscription 157.0 130.8 440.7 366.3 Technical support 121.4 96.1 347.4 267.3 Professional services and training 11.0 10.2 32.5 29.6 Total service revenue 289.4 237.1 820.6 663.2 Total revenue $ 453.9 $ 374.2 $ 1,294.2 $ 1,078.3 (1) As noted above, prior period amounts have not been adjusted under the modified retrospective method. Transaction Price Allocated to the Remaining Performance Obligations As of September 30, 2018 , we had $1.54 billion in remaining performance obligations, which is substantially comprised of deferred security subscription and technical support services not yet delivered. We expect to recognize revenue on approximately 80% of these remaining performance obligations over the next one to two years, with the remaining balance to be recognized in three to five years. Accounts Receivable Trade accounts receivable are recorded at the invoiced amount. Trade accounts receivable is reduced by allowance for doubtful accounts which is determined based on our assessment of the collectability of customer accounts. The allowance for doubtful accounts was $0.7 million and $0.9 million as of September 30, 2018 and December 31, 2017, respectively. As of December 31, 2017, accounts receivable was also reduced by sales return reserve of $13.6 million which we reclassified to accrued liabilities account as of January 1, 2018 in accordance with the adoption of Topic 606. Contract Assets Contract assets represent amounts that have been recognized as revenue but for which we did not have the unconditional right to invoice the customer. Contract assets were insignificant as of September 30, 2018 and January 1, 2018. Deferred Contract Costs Sales commissions earned by our sales force are considered incremental and recoverable costs of obtaining a contract with a customer. Sales commissions for the sale of products and software licenses are recognized at the time of sale. Sales commissions for initial service contracts are deferred and then amortized as an expense on a straight-line basis over the period of benefit which we have determined to be five years. We determined the period of benefit taking into consideration our customer contracts, our technology and other factors. Sales commissions for renewal contracts are deferred and then amortized on a straight line basis over the contractual period of the underlying contracts which ranges from one to three years and, to a lesser extent, five years. The amortization of deferred contract costs is included in sales and marketing expense in our condensed consolidated statement of operations. Amortization of deferred contract costs during the three and nine months ended September 30, 2018 was $23.2 million and $66.3 million , respectively. No impairment loss was recognized during the three and nine months ended September 30, 2018 . Practical Expedient We elected to use the contract modification practical expedient. This practical expedient allows for all contract modifications before January 1, 2018 to be aggregated and evaluated at adoption date. Impact on Condensed Consolidated Financial Statements The following tables summarize the impact of adopting Topic 606 on our condensed consolidated financial statements as of and for the three and nine months ended September 30, 2018 (in millions). These tables do not represent the full condensed consolidated financial statements as they only reflect the accounts impacted by the adoption of Topic 606. Condensed Consolidated Balance Sheet As of September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase (Decrease) Assets: Accounts receivable $ 324.4 $ 310.7 $ 13.7 Inventory $ 80.8 $ 81.9 $ (1.1 ) Deferred contract costs $ 169.6 $ — $ 169.6 Deferred tax assets $ 147.8 $ 175.6 $ (27.8 ) Liabilities: Accrued liabilities $ 60.7 $ 45.5 $ 15.2 Deferred revenue, current $ 876.2 $ 896.6 $ (20.4 ) Deferred revenue, non-current $ 668.2 $ 667.0 $ 1.2 Other liabilities, non-current $ 11.1 $ 5.2 $ 5.9 Stockholders’ Equity Accumulated deficit $ (156.0 ) $ (308.5 ) $ 152.5 Condensed Consolidated Statement of Operations Three Months Ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase (Decrease) REVENUE: Product (1) $ 164.5 $ 162.3 $ 2.2 Service 289.4 289.6 (0.2 ) Total revenue 453.9 451.9 2.0 COSTS OF REVENUE: Product 72.0 72.3 (0.3 ) GROSS PROFIT: Product 92.5 90.0 2.5 Service 249.8 250.0 (0.2 ) Total gross profit 342.3 340.0 2.3 OPERATING EXPENSES: Sales and marketing expenses 198.3 207.3 (9.0 ) OPERATING INCOME 62.8 51.5 11.3 INCOME BEFORE INCOME TAXES 70.6 59.3 11.3 PROVISION FOR INCOME TAXES 11.9 9.8 2.1 NET INCOME $ 58.7 $ 49.5 $ 9.2 Net income per share: Basic $ 0.35 $ 0.29 $ 0.05 Diluted $ 0.33 $ 0.28 $ 0.05 (1) Product revenue during the three months ended September 30, 2018 included a $2.2 million benefit from the adoption of Topic 606, which primarily related to the change in accounting treatment under Topic 606 for some of our software products where revenue from these arrangements is now recognized upfront instead of ratably over the contracted service term. Nine Months Ended September 30, 2018 As Reported Balances Without Adoption of Effect of Change REVENUE: Product (1) $ 473.6 $ 461.5 $ 12.1 Service 820.6 819.1 1.5 Total revenue 1,294.2 1,280.6 13.6 COST OF REVENUE: Product 204.1 203.1 1.0 GROSS PROFIT: Product 269.5 258.4 11.1 Service 702.8 701.3 1.5 Total gross profit 972.3 959.7 12.6 OPERATING EXPENSES Sales and marketing expenses 576.4 608.9 (32.5 ) OPERATING INCOME 145.9 100.8 45.1 INCOME BEFORE INCOME TAXES 158.8 113.7 45.1 BENEFIT FROM INCOME TAXES 9.2 (0.7 ) 9.9 NET INCOME $ 149.6 $ 114.4 $ 35.2 Net income per share: Basic $ 0.89 $ 0.68 $ 0.21 Diluted $ 0.86 $ 0.66 $ 0.20 (1) Product revenue during the nine months ended September 30, 2018 included a $12.1 million benefit from the adoption of Topic 606, which primarily related to the change in accounting treatment under Topic 606 for some of our software products where revenue from these arrangements is now recognized upfront instead of ratably over the contracted service term. Condensed Consolidated Statement of Cash Flows Nine Months Ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase (Decrease) Cash flows from operating activities: Net income $ 149.6 $ 114.4 $ 35.2 Adjustments to reconcile net income to net cash provided by operating activities: Amortization of deferred contract costs 66.3 — 66.3 Other (1.7 ) (1.6 ) (0.1 ) Changes in operating assets and liabilities: Inventory (19.0 ) (20.0 ) 1.0 Deferred contract costs (98.8 ) — (98.8 ) Deferred tax assets (19.1 ) (29.0 ) 9.9 Accrued liabilities (2.0 ) (3.5 ) 1.5 Deferred revenue 209.9 224.9 (15.0 ) Net cash provided by operating activities $ 458.7 $ 458.7 $ —

Financial Instruments and Fair

Financial Instruments and Fair Value	9 Months Ended
	Sep. 30, 2018
Financial Instruments and Fair Value [Abstract]
FINANCIAL INSTRUMENTS AND FAIR VALUE	FINANCIAL INSTRUMENTS AND FAIR VALUE The following tables summarize our investments (in millions): September 30, 2018 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate debt securities $ 296.6 $ — $ (1.2 ) $ 295.4 Certificates of deposit and term deposits (1) 106.1 — — 106.1 Commercial paper 72.5 — (0.1 ) 72.4 U.S. government and agency securities 29.7 — (0.1 ) 29.6 Total available-for-sale securities $ 504.9 $ — $ (1.4 ) $ 503.5 December 31, 2017 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate debt securities $ 391.0 $ — $ (1.2 ) $ 389.8 Commercial paper 74.2 — — 74.2 Certificates of deposit and term deposits (1) 45.9 — — 45.9 U.S. government and agency securities 28.5 — (0.1 ) 28.4 Total available-for-sale securities $ 539.6 $ — $ (1.3 ) $ 538.3 (1) The majority of our certificates of deposit and term deposits are foreign deposits. The following tables show the gross unrealized losses and the related fair values of our investments that have been in a continuous unrealized loss position (in millions): September 30, 2018 Less Than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate debt securities $ 163.1 $ (0.3 ) $ 94.5 $ (0.9 ) $ 257.6 $ (1.2 ) Commercial paper 90.5 (0.1 ) — — 90.5 (0.1 ) Certificates of deposit and term deposits 35.9 — — — 35.9 — U.S. government and agency securities 26.2 — 3.5 (0.1 ) 29.7 (0.1 ) Total available-for-sale securities $ 315.7 $ (0.4 ) $ 98.0 $ (1.0 ) $ 413.7 $ (1.4 ) December 31, 2017 Less Than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate debt securities $ 317.4 $ (0.9 ) $ 58.2 $ (0.3 ) $ 375.6 $ (1.2 ) Certificates of deposit and term deposits 37.2 — — — 37.2 — Commercial paper 29.0 — — — 29.0 — U.S. government and agency securities 17.0 — 11.4 (0.1 ) 28.4 (0.1 ) Total available-for-sale securities $ 400.7 $ (0.9 ) $ 69.6 $ (0.4 ) $ 470.3 $ (1.3 ) The contractual maturities of our investments were as follows (in millions): September 30, December 31, Due within one year $ 464.9 $ 440.3 Due within one to three years 38.6 98.0 Total $ 503.5 $ 538.3 Available-for-sale securities are reported at fair value, with unrealized gains and losses and the related tax impact included as a separate component of stockholders’ equity and in comprehensive income. Realized losses on available-for-sale securities were insignificant in the periods presented and are included in other income (expense)—net in our condensed consolidated statements of operations. We use the specific identification method to determine the cost basis of investments sold. The unrealized losses on our available-for-sale securities were caused by fluctuations in market value and interest rates as a result of the economic environment. As the decline in market value are attributable to changes in market conditions and not credit quality, and because we have concluded currently that we neither intend to sell nor is it more likely than not that we will be required to sell these investments prior to a recovery of par value, we do not consider these investments to be other-than temporarily impaired as of September 30, 2018 . Fair Value Accounting—We apply the following fair value hierarchy for disclosure of the inputs used to measure fair value. This hierarchy prioritizes the inputs into three broad levels as follows: Level 1—Inputs are unadjusted quoted prices in active markets for identical assets or liabilities. Level 2—Inputs are quoted prices for similar assets and liabilities in active markets or inputs that are observable for the assets or liabilities, either directly or indirectly through market corroboration, for substantially the full term of the financial instruments. Level 3—Unobservable inputs based on our own assumptions used to measure assets and liabilities at fair value. The inputs require significant management judgment or estimation. We measure the fair value of money market funds and certain U.S. government and agency securities using quoted prices in active markets for identical assets. The fair value of all other financial instruments was based on quoted prices for similar assets in active markets, or on model-driven valuations using significant inputs derived from or corroborated by observable market data. We classify investments within Level 1 if quoted prices are available in active markets for identical securities. We classify items within Level 2 if the investments are valued using model-driven valuations using observable inputs such as quoted market prices, benchmark yields, reported trades, broker/dealer quotes or alternative pricing sources with reasonable levels of price transparency. Investments are held by custodians who obtain investment prices from a third-party pricing provider that incorporates standard inputs in various asset price models. Fair Value of Financial Instruments Assets Measured at Fair Value on a Recurring Basis The following tables present the fair value of our financial assets measured at fair value on a recurring basis as of September 30, 2018 and December 31, 2017 (in millions): September 30, 2018 December 31, 2017 Aggregate Fair Value Quoted Prices in Active Markets For Identical Assets Significant Other Observable Remaining Inputs Significant Other Unobservable Remaining Inputs Aggregate Fair Value Quoted Prices in Active Markets For Identical Assets Significant Other Observable Remaining Inputs Significant Other Unobservable Remaining Inputs (Level 1) (Level 2) (Level 3) (Level 1) (Level 2) (Level 3) Assets: Corporate debt securities $ 295.4 $ — $ 295.4 $ — $ 411.1 $ — $ 411.1 $ — Certificates of deposit and term deposits 228.3 — 228.3 — 132.1 — 132.1 — Money market funds 139.0 139.0 — — 195.6 195.6 — — Commercial paper 121.0 — 121.0 — 128.9 — 128.9 — U.S. government and agency securities 29.6 26.1 3.5 — 28.4 24.9 3.5 — Total $ 813.3 $ 165.1 $ 648.2 $ — $ 896.1 $ 220.5 $ 675.6 $ — Reported as: Cash equivalents $ 309.8 $ 357.8 Short-term investments 464.9 440.3 Long-term investments 38.6 98.0 Total $ 813.3 $ 896.1 There were no transfers between Level 1 and Level 2 of the fair value hierarchy during the nine months ended September 30, 2018 and year ended December 31, 2017 .

Inventory

Inventory	9 Months Ended
	Sep. 30, 2018
Inventory Disclosure [Abstract]
INVENTORY	INVENTORY Inventory consisted of the following (in millions): September 30, December 31, Raw materials $ 12.5 $ 13.0 Finished goods 68.3 64.3 Inventory $ 80.8 $ 77.3 Inventory includes materials at contract manufacturers of $2.9 million and $2.6 million as of September 30, 2018 and December 31, 2017 , respectively. Inventory also includes finished goods held by distributors where revenue is recognized on a sell-through basis of $0.1 million as of December 31, 2017.

Property and Equipment_Net

Property and Equipment—Net	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT—Net	PROPERTY AND EQUIPMENT—Net Property and equipment—net consisted of the following (in millions): September 30, December 31, Building and building improvements $ 138.6 $ 133.2 Computer equipment and software 95.0 79.9 Land 75.7 65.6 Leasehold improvements 21.9 20.8 Evaluation units 20.2 20.1 Furniture and fixtures 16.7 14.7 Construction-in-progress 11.5 6.3 Total property and equipment 379.6 340.6 Less: accumulated depreciation (114.2 ) (95.2 ) Property and equipment—net $ 265.4 $ 245.4 Depreciation expense was $11.8 million and $11.7 million during the three months ended September 30, 2018 and September 30, 2017 , respectively. Depreciation expense was $34.9 million and $34.7 million during the nine months ended September 30, 2018 and September 30, 2017 , respectively.

Investments in Privately-Held C

Investments in Privately-Held Companies	9 Months Ended
	Sep. 30, 2018
Investments, All Other Investments [Abstract]
INVESTMENTS IN PRIVATELY-HELD COMPANIES	INVESTMENTS IN PRIVATELY HELD COMPANIES Our investments in the equity securities of privately held companies totaled $9.1 million as of September 30, 2018 and $12.1 million as of December 31, 2017 . These investments, which were previously accounted for at cost, are now accounted for at cost, adjusted for changes in observable prices minus impairment. We own less than 20% of the voting securities in each of these investments and do not have the ability to exercise significant influence over operating and financial policies of the respective entities. These investments are carried at historical cost and are recorded as other assets on our condensed consolidated balance sheets and would be measured at fair value if indicators of impairment existed. During the three months ended September 30, 2018 , we sold equity securities of a privately held company for $5.2 million and recognized a gain of $2.2 million as other income in our condensed consolidated statements of operations. As of September 30, 2018 , no other events have occurred that would adversely affect the carrying value of our remaining investments. As of September 30, 2018 , we determined that we had a variable interest in these privately held companies. However, we determined that we were not the primary beneficiary as we did not have the power to direct their activities that most significantly affect their economic performance. The variable interest entities are not required to be consolidated in our condensed consolidated financial statements.

Business Combination

Business Combination	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
BUSINESS COMBINATION	BUSINESS COMBINATION Bradford Networks, Inc. On June 4, 2018, we acquired all outstanding shares of Bradford Networks, Inc. (“Bradford”), a provider of network access control security products and services. We believe that this acquisition will extend the Fortinet Security Fabric to include network access control and provide for the security assessment and response related to devices accessing the network, including Internet of Things devices. Under the business combination method of accounting, the total purchase price was allocated to Bradford’s net tangible and intangible assets based upon their estimated fair values as of June 4, 2018. The purchase price allocation was preliminary and was based on management's best estimates and assumptions as of the reporting date. During the three months ended September 30, 2018, we subsequently decreased the intangible assets by $0.8 million with a corresponding change to goodwill of $0.6 million and deferred tax asset of $0.2 million . The preliminary purchase price for Bradford was $6.8 million , of which $11.1 million was allocated to goodwill that was non-deductible for tax purposes, and $8.0 million was allocated to identifiable intangible assets offset by $12.3 million of net liabilities assumed. We may pay an additional $2.0 million in cash consideration as an earn-out that is subject in full to satisfaction of certain performance conditions. As of September 30, 2018, no fair value was assigned to the contingent consideration based on the estimated probability of attainment of the target. Pro forma information has not been presented for these acquisitions as the impact to our Condensed Consolidated Financial Statements was not material.

Goodwill and Other Intangible A

Goodwill and Other Intangible Assets - Net	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND OTHER INTANGIBLE ASSETS - Net	GOODWILL AND OTHER INTANGIBLE ASSETS—Net Goodwill Changes in the carrying value of goodwill were (in millions): Amount Balance—December 31, 2017 $ 14.6 Addition due to business combination 11.1 Balance—September 30, 2018 $ 25.7 There were no impairments to goodwill during the three and nine months ended September 30, 2018. Other Intangible Assets—net The following tables present other intangible assets—net as of September 30, 2018 and December 31, 2017 (in millions, except years): September 30, 2018 Weighted-Average Useful Life (in Years) Gross Accumulated Amortization Net Other intangible assets—net: Finite-lived intangible assets: Developed technologies and other 3.8 $ 31.4 $ 18.1 $ 13.3 Customer relationships 4.5 16.7 11.9 4.8 Total other intangible assets—net $ 48.1 $ 30.0 $ 18.1 December 31, 2017 Weighted-Average Useful Life (in Years) Gross Accumulated Amortization Net Other intangible assets—net: Finite-lived intangible assets: Developed technologies and other 3.8 $ 24.0 $ 13.7 $ 10.3 Customer relationships 4.7 14.5 10.1 4.4 38.5 23.8 14.7 Indefinite-lived intangible assets: In-process research and development 1.6 — 1.6 Total other intangible assets—net $ 40.1 $ 23.8 $ 16.3 The in-process research and development intangible asset of $1.6 million was completed in the three months ended March 31, 2018. Upon completion, the cost was transferred to developed technology and is amortized over the estimated useful life of four years. Amortization expense was $2.5 million and $2.0 million during the three months ended September 30, 2018 and September 30, 2017 , respectively. Amortization expense was $6.1 million and $6.5 million during the nine months ended September 30, 2018 and September 30, 2017 , respectively. The following table summarizes estimated future amortization expense of finite-lived intangible assets—net (in millions): Amount Years: 2018 $ 2.5 2019 8.2 2020 4.6 2021 and thereafter 2.8 Total $ 18.1

Net Income Per Share

Net Income Per Share	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
NET INCOME PER SHARE	NET INCOME PER SHARE Basic net income per share is computed by dividing net income by the weighted-average number of shares of common stock outstanding during the period. Diluted net income per share is computed by dividing net income by the weighted-average number of shares of common stock outstanding during the period, plus the dilutive effects of restricted stock units (“RSUs”), stock options and the Employee Stock Purchase Plan (the “ESPP”). Dilutive shares of common stock are determined by applying the treasury stock method. A reconciliation of the numerator and denominator used in the calculation of basic and diluted net income per share is as follows (in millions, except per share amounts): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Numerator: Net income $ 58.7 $ 26.7 $ 149.6 $ 60.4 Denominator: Basic shares: Weighted-average common stock outstanding-basic 169.8 175.5 168.7 175.3 Diluted shares: Weighted-average common stock outstanding-basic 169.8 175.5 168.7 175.3 Effect of potentially dilutive securities: RSUs 4.2 2.1 3.5 2.2 Stock options 1.6 1.3 1.4 1.4 ESPP 0.1 0.1 0.1 0.1 Weighted-average shares used to compute diluted net income per share 175.7 179.0 173.7 179.0 Net income per share: Basic $ 0.35 $ 0.15 $ 0.89 $ 0.34 Diluted $ 0.33 $ 0.15 $ 0.86 $ 0.34 The following weighted-average shares of common stock were excluded from the computation of diluted net income per share for the periods presented, as their effect would have been antidilutive (in millions): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, RSUs 0.3 1.0 0.6 1.6 Stock options — 1.1 0.4 1.1 ESPP 0.2 0.4 0.1 0.2 Total 0.5 2.5 1.1 2.9

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES The following table summarizes our future principal contractual obligations as of September 30, 2018 (in millions): Total 2018 2019 2020 2021 2022 Thereafter Operating lease commitments $ 52.0 $ 4.1 $ 15.3 $ 11.6 $ 8.0 $ 5.0 $ 8.0 Inventory purchase commitments 174.0 111.1 58.7 4.2 — — — Total $ 226.0 $ 115.2 $ 74.0 $ 15.8 $ 8.0 $ 5.0 $ 8.0 Operating Leases —We lease certain facilities under various non-cancelable operating leases, which expire through 2026. Certain leases require us to pay variable costs such as taxes, maintenance, and insurance. The terms of certain operating leases also provide for renewal options and escalation clauses. Rent expense was $4.4 million and $4.1 million during the three months ended September 30, 2018 and September 30, 2017 , respectively. Rent expense was $13.1 million and $12.5 million during the nine months ended September 30, 2018 and September 30, 2017 , respectively. Rent expense is recognized using the straight-line method over the term of the lease. Inventory Purchase Commitments —Our independent contract manufacturers procure components and build our products based on our forecasts. These forecasts are based on estimates of future demand for our products, which are in turn based on historical trends and an analysis from our sales and marketing organizations, adjusted for overall market conditions. In order to reduce manufacturing lead times and plan for adequate component supply, we may issue purchase orders to some of our independent contract manufacturers which may not be cancelable. As of September 30, 2018 , we had $174.0 million of open purchase orders with our independent contract manufacturers that may not be cancelable. Other Contractual Commitments and Open Purchase Orders —In addition to commitments with contract manufacturers, we have open purchase orders and contractual obligations in the ordinary course of business for which we have not received goods or services. As of September 30, 2018 , we had $11.6 million in other contractual commitments having a remaining term in excess of one year that may not be cancelable. Litigation —We are involved in disputes, litigation, and other legal actions. For lawsuits where we are the defendant, we are in the process of defending these litigation matters, and there can be no assurances and the outcome of these matters is currently not determinable. There are many uncertainties associated with any litigation and these actions or other third-party claims against us may cause us to incur costly litigation fees, including contingent legal fees with related parties, costs and substantial settlement charges, and possibly subject us to damages and other penalties. In addition, the resolution of any intellectual property litigation may require us to make royalty payments, which could adversely affect our gross margins in future periods. If any of those events were to occur, our business, financial condition, results of operations, and cash flows could be adversely affected. The actual liability in any such matters may be materially different from our estimates, if any, which could result in the need to adjust the liability and record additional expenses. As required under ASC 450, Contingencies, issued by the FASB, we accrue for contingencies when we believe that a loss is probable and that we can reasonably estimate the amount of any such loss. As previously disclosed, in October 2016, we received a letter from the United States Attorney’s Office for the Northern District of California requesting information relating to our compliance with the Trade Agreements Act. We have been fully cooperating with this ongoing inquiry and have periodically met and spoken with the United States Attorney’s Office in connection with this matter. We are currently in settlement discussions with the United States Attorney’s Office. Indemnification —Under the indemnification provisions of our standard sales contracts, we agree to defend our customers against third-party claims asserting various allegations such as product defects and infringement of certain intellectual property rights, which may include patents, copyrights, trademarks or trade secrets, and to pay judgments entered on such claims. In some contracts, our exposure under these indemnification provisions is limited by the terms of the contracts to certain defined limits, such as the total amount paid by our customer under the agreement. However, certain agreements include covenants, penalties and indemnification provisions including and beyond indemnification for third-party claims of intellectual property infringement, that could potentially expose us to losses in excess of the amount received under the agreement, and in some instances to potential liability that is not contractually limited. To date, although from time to time there are indemnification claims asserted against us and currently there are pending indemnification claims, there have been no material awards under such indemnification provisions.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCKHOLDERS' EQUITY	STOCKHOLDERS’ EQUITY Stock-Based Compensation Plans We have stock-based compensation plans pursuant to which we have granted RSUs and stock options. We also have an ESPP for eligible employees. As of September 30, 2018 , there were a total of 54.5 million shares of common stock available for grant under our stock-based compensation plans. Restricted Stock Units The following table summarizes the activity and related information for RSUs for the periods presented below (in millions, except per share amounts): Restricted Stock Units Outstanding Number of Shares Weighted-Average Grant Date Fair Value per Share Balance—December 31, 2017 8.5 $ 34.79 Granted 3.7 54.82 Forfeited (0.7 ) 38.24 Vested (3.1 ) 34.32 Balance—September 30, 2018 8.4 $ 44.48 As of September 30, 2018 , total compensation expense related to unvested RSUs granted to employees and non-employees under the 2009 Plan, but not yet recognized, was $331.7 million . This expense is expected to be amortized on a straight-line basis over a weighted-average vesting period of 2.8 years. RSUs settle into shares of common stock upon vesting. Upon the vesting of the RSUs, we net-settle the RSUs and withhold a portion of the shares to satisfy minimum statutory employee withholding taxes. Total payment for the employees’ tax obligations to the taxing authorities is reflected as a financing activity within the condensed consolidated statements of cash flows. The following summarizes the number and value of the shares withheld for employee taxes (in millions): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Shares withheld for taxes 0.2 0.3 0.9 1.0 Amount withheld for taxes $ 15.5 $ 10.0 $ 48.0 $ 35.9 Employee Stock Options The following table summarizes the weighted-average assumptions relating to our employee stock options: Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Expected term in years 4.4 4.4 4.4 4.4 Volatility 30.5 % 33.1 % 31.6 % 36.1 % Risk-free interest rate 2.7 % 1.8 % 2.7 % 1.9 % Dividend rate — % — % — % — % The following table summarizes the stock option activity and related information for the periods presented below (in millions, except exercise prices and contractual life): Options Outstanding Number of Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (Years) Aggregate Intrinsic Value Balance—December 31, 2017 4.3 $ 27.50 Granted 0.8 51.29 Forfeited (0.1 ) 31.90 Exercised (1.8 ) 24.74 Balance—September 30, 2018 3.2 $ 34.69 Options vested and expected to vest—September 30, 2018 3.2 $ 34.69 4.13 $ 183.4 Options exercisable—September 30, 2018 1.6 $ 28.42 2.75 $ 104.9 The aggregate intrinsic value represents the difference between the exercise price of stock options and the quoted market price of our common stock on September 30, 2018 , for all in-the-money stock options. As of September 30, 2018 , total compensation expense related to unvested stock options granted to employees but not yet recognized was $18.1 million . This expense is expected to be amortized on a straight-line basis over a weighted-average period of 2.7 years. Additional information related to our stock options is summarized below (in millions, except per share amounts): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Weighted-average fair value per share granted $ 22.75 $ 11.09 $ 15.67 $ 12.17 Intrinsic value of options exercised 14.1 3.4 53.6 30.3 Fair value of options vested 1.4 1.6 5.7 6.7 Employee Stock Purchase Plan In determining the fair value of the ESPP, we use the Black-Scholes option pricing model that employs the following weighted-average assumptions: Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Expected term in years 0.5 0.5 0.5 0.5 Volatility 30.5 % 26.2 % 28.9 % 29.5 % Risk-free interest rate 2.2 % 1.2 % 2.0 % 0.9 % Dividend rate — % — % — % — % Additional information related to the ESPP is provided below (in millions, except per share amounts): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Weighted-average fair value per share granted $ 18.28 $ 8.31 $ 14.14 $ 8.73 Shares issued under the ESPP 0.4 0.5 1.1 1.1 Weighted-average price per share issued $ 41.89 $ 31.49 $ 35.32 $ 29.52 Stock-based Compensation Expense Stock-based compensation expense is included in costs and expenses as follows (in millions): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Cost of product revenue $ 0.3 $ 0.3 $ 1.1 $ 1.0 Cost of service revenue 2.8 2.4 8.0 7.2 Research and development 9.3 8.0 26.9 24.1 Sales and marketing 26.0 19.6 70.5 58.4 General and administrative 4.8 4.0 13.8 12.0 Total stock-based compensation expense $ 43.2 $ 34.3 $ 120.3 $ 102.7 The following table summarizes stock-based compensation expense by award type (in millions): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, RSUs $ 38.2 $ 29.9 $ 106.1 $ 89.8 Stock options 2.4 1.8 6.7 5.6 ESPP 2.6 2.6 7.5 7.3 Total stock-based compensation expense $ 43.2 $ 34.3 $ 120.3 $ 102.7 Total income tax benefit associated with stock-based compensation that is recognized in the consolidated statements of operations is as follows (in millions): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Income tax benefit associated with stock-based compensation $ 6.8 $ 6.7 $ 19.0 $ 21.1 Share Repurchase Program In January 2016, our board of directors approved a Share Repurchase Program (the “Repurchase Program”), which authorized the repurchase of up to $200.0 million of our outstanding common stock through December 31, 2017. In 2016 and 2017, our board of directors approved the increases in the aggregate authorized repurchase amount under the Repurchase Program by $100.0 million and $700.0 million , respectively, to a total of $1.0 billion . In July 2018, our board of directors approved a $500.0 million increase in the authorized stock repurchase under the Repurchase Program and extended the term of the Repurchase Program to December 31, 2019, bringing the aggregate amount authorized to be repurchased to $1.5 billion of our outstanding common stock through December 31, 2019. Under the Repurchase Program, share repurchases may be made by us from time to time in privately negotiated transactions or in open market transactions. The Repurchase Program does not require us to purchase a minimum number of shares, and may be suspended, modified or discontinued at any time without prior notice. During the three months ended September 30, 2018, we did not repurchase shares under the Repurchase Program. During the nine months ended September 30, 2018 , we repurchased 2,540,547 shares of common stock under the Repurchase Program in open market transactions at an average price of $46.08 per share, for an aggregate purchase price of $117.1 million . As of September 30, 2018 , $825.8 million remained available for future share repurchases under the Repurchase Program.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES Our effective tax rate was 17% for the three months ended September 30, 2018 , compared to an effective tax rate of 30% for the same period last year. Our effective tax rate was 6% for the nine months ended September 30, 2018 , compared to an effective tax rate of 24% for the same period last year, with the primary difference being the change in the federal corporate income tax rate to 21% in 2018 from 35% in the prior year, the release of reserve for uncertain tax positions including interest due to a statute of limitation expiring and the completion of the Internal Revenue Service (“IRS”) audit. The effective tax rates for the periods presented are comprised of U.S. federal and state taxes, withholding taxes and foreign taxes, excess tax benefits from stock-based compensation and release of a reserve for uncertain tax positions. The tax rates for the three months ended September 30, 2018 and September 30, 2017 were impacted by U.S. federal and state taxes, withholding taxes and foreign taxes of $17.7 million and $12.7 million , respectively, which were offset by a tax provision benefit of $5.8 million and $1.8 million , respectively, for stock-based compensation. The tax rate for the nine months ended September 30, 2018 and September 30, 2017 were impacted by withholding taxes and foreign taxes of $43.4 million and $30.0 million , respectively, which were offset by a tax benefit of $16.2 million and $11.4 million , respectively, for stock-based compensation. The tax rate for the nine months ended September 30, 2018 was also impacted by release of reserve for uncertain tax positions including interest of $18.0 million . Our effective tax rates fluctuate based on the amount of pre-tax income or loss. The impact of discrete items, such as excess tax benefits from stock-based compensation, on our effective tax rate is greater when our pre-tax income is lower. As of September 30, 2018 and December 31, 2017 , unrecognized tax benefits were $64.1 million and $72.5 million , respectively. The amount of $62.8 million in unrecognized tax benefits, if recognized, would favorably affect our effective tax rate. It is our policy to include accrued interest and penalties related to uncertain tax benefits in income tax expense. As of September 30, 2018 and December 31, 2017 , accrued interest and penalties were $12.2 million and $13.5 million , respectively. It is reasonably possible that our gross unrecognized tax benefits will decrease by up to $8.0 million in the next 12 months, primarily due to the lapse of the statute of limitations. These adjustments, if recognized, would positively impact our effective tax rate, and would be recognized as additional tax benefits. We file income tax returns in the U.S. federal jurisdiction and in various U.S. state and foreign jurisdictions. Generally, we are no longer subject to U.S. state and non-U.S. income tax examinations by tax authorities for tax years prior to 2008. We are no longer subject to examination by U.S federal income tax authorities for tax years prior to 2015. We have closed the Internal Revenue Service audit for tax years 2012, 2013 and 2014. In March 2018, we received a refund of $6.8 million for a carry-back claim approved in this audit. In October 2018, the French tax authorities notified us that they had closed the audit for tax years from 2007 to 2015 with no tax adjustment. This audit was examining the intercompany relationship between Fortinet, Inc., Fortinet France and Fortinet Singapore. In April 2018, the tax authorities in Israel initiated a tax audit for tax years from 2008 to 2014. In July 2018, the tax authorities in Italy initiated a tax audit for tax year 2015. On July 24, 2018, the U.S. Court of Appeals for the Ninth Circuit overturned the U.S. Tax Court’s unanimous 2015 decision in Altera v. Commissioner , holding that the IRS did not violate the rulemaking procedures required by the Administrative Procedures Act. On August 7, 2018, the Ninth Circuit withdrew the opinions filed on July 24, 2018 to allow time for the reconstituted panel to confer on the appeal. In Altera , the taxpayer challenged IRS regulations that required participants in qualified cost sharing arrangements to share stock-based compensation costs. The U.S. Tax Court had invalidated those regulations, in part because the Treasury Department failed to adequately consider significant taxpayer comments when adopting them. We will evaluate the tax impact when the new opinion is released by the Ninth Circuit.

Defined Contribution Plans

Defined Contribution Plans	9 Months Ended
	Sep. 30, 2018
Retirement Benefits [Abstract]
DEFINED CONTRIBUTION PLANS	DEFINED CONTRIBUTION PLANS Our tax-deferred savings plan under our 401(k) Plan, permits participating employees to defer a portion of their pre-tax earnings. In Canada, we have a Group Registered Retirement Savings Plan Program (the “RRSP”), which permits participants to make tax deductible contributions. Our board of directors approved 50% matching contributions on employee contributions up to 4% of each employee’s eligible earnings. Our matching contributions to our 401(k) Plan and the RRSP for the three months ended September 30, 2018 and September 30, 2017 were $1.4 million and $1.2 million , respectively. Our matching contributions to our 401(k) Plan and the RRSP for the nine months ended September 30, 2018 and September 30, 2017 were $4.4 million and $3.8 million , respectively.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
SEGMENT INFORMATION	SEGMENT INFORMATION Operating segments are defined as components of an enterprise about which separate financial information is available that is evaluated regularly by the chief operating decision maker in deciding how to allocate resources and in assessing performance. Our chief operating decision maker is our chief executive officer. Our chief executive officer reviews financial information presented on a consolidated basis, accompanied by information about revenue by geographic region for purposes of allocating resources and evaluating financial performance. We have one business activity, and there are no segment managers who are held accountable for operations, operating results and plans for levels or components below the consolidated unit level. Accordingly, we have determined that we have one operating segment, and therefore, one reportable segment. Revenue by geographic region is based on the billing address of our distributors and direct customer. The following tables set forth revenue and property and equipment—net by geographic region (in millions): Three Months Ended Nine Months Ended Revenue September 30, September 30, September 30, September 30, Americas: United States $ 146.8 $ 123.7 $ 425.3 $ 367.1 Latin America (“LATAM”) 31.2 24.4 86.4 64.6 Canada 16.0 13.1 47.4 36.6 Total Americas 194.0 161.2 559.1 468.3 Europe, Middle East and Africa (“EMEA”) 165.4 138.3 474.3 394.2 Asia Pacific (“APAC”) 94.5 74.7 260.8 215.8 Total revenue $ 453.9 $ 374.2 $ 1,294.2 $ 1,078.3 Property and Equipment — net September 30, December 31, Americas: United States $ 127.8 $ 115.6 Canada 111.1 103.8 LATAM 0.4 0.3 Total Americas 239.3 219.7 EMEA: France 13.3 11.9 Other EMEA 3.5 5.8 Total EMEA 16.8 17.7 APAC 9.3 8.0 Total property and equipment—net $ 265.4 $ 245.4 The following customers, each of which is a distributor, accounted for 10% or more of our revenue: Three Months Ended Nine Months Ended September 30, 2018 (1) September 30, September 30, 2018 (1) September 30, Exclusive Networks Group 29 % 29 % 29 % 23 % Ingram Micro 11 % 11 % 10 % 10 % (1) Due to the acquisition by Exclusive Networks Group of the U.S. division of Fine Tec Computers (“Fine Tec U.S.”) in July 2017, Fine Tec U.S.’s revenue and accounts receivable have been combined with Exclusive Networks Group. The following customer, which is a distributor, accounted for 10% or more of net accounts receivable: September 30, December 31, Exclusive Networks Group 33 % 35 % Ingram Micro 10 % * * Represents less than 10%

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	9 Months Ended
	Sep. 30, 2018
Other Comprehensive Income (Loss), Net of Tax [Abstract]
ACCUMULATED OTHER COMPREHENSIVE LOSS	ACCUMULATED OTHER COMPREHENSIVE LOSS The following table summarizes the changes in accumulated balances of other comprehensive loss (in millions): Unrealized Losses on Investments Tax provision related to unrealized gains or losses on investments Total Balance—December 31, 2017 $ (1.3 ) $ 0.5 $ (0.8 ) Other comprehensive loss before reclassifications (0.1 ) (0.1 ) (0.2 ) Amounts reclassified from accumulated other comprehensive loss — — — Net current-period other comprehensive loss (0.1 ) (0.1 ) (0.2 ) Balance—September 30, 2018 $ (1.4 ) $ 0.4 $ (1.0 ) Amounts reclassified from accumulated other comprehensive loss for unrealized losses on investments and tax provision related to unrealized gains or losses on investments are recorded in other income (expense)—net and in benefit from income taxes, respectively.

Subsequent Event

Subsequent Event	9 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
SUBSEQUENT EVENT	SUBSEQUENT EVENT On October 23, 2018, we acquired ZoneFox Limited (“ZoneFox”), a privately held cloud-based insider threat detection and response company headquartered in Edinburgh, Scotland. The integration of ZoneFox’s machine learning-based threat-hunting technology will provide endpoint detection and response capabilities and will extend FortiSIEM product with additional user entity behavior analytics features, both on-premises and in the cloud. We acquired ZoneFox for approximately $18 million in initial consideration, subject to certain adjustments. We are currently in the process of evaluating the business combination accounting considerations, including the consideration transferred and the initial purchase price allocation.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Basis of Presentation and Preparation	Basis of Presentation and Preparation —The unaudited condensed consolidated financial statements of Fortinet, Inc. and its wholly owned subsidiaries (collectively, “we,” “us” or “our”) have been prepared in accordance with generally accepted accounting principles in the United States (“GAAP”) for interim financial information, as well as the instructions to Form 10-Q pursuant to the rules and regulations of the U.S. Securities and Exchange Commission (the “SEC”). Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements, and should be read in conjunction with our audited consolidated financial statements as of and for the year ended December 31, 2017, contained in our Annual Report on Form 10-K filed with the SEC on February 26, 2018 (the “Form 10-K”). In the opinion of management, all adjustments, which includes normal recurring adjustments, considered necessary for a fair presentation have been included. All intercompany balances, transactions and cash flows have been eliminated. The results of operations for the three and nine months ended September 30, 2018 are not necessarily indicative of the results for the full year or for any future periods. The condensed consolidated balance sheet as of December 31, 2017 is derived from the audited consolidated financial statements for the year ended December 31, 2017. The preparation of financial statements in accordance with GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Actual results could differ materially from those estimates. There have been no material changes to our significant accounting policies as of and for the three and nine months ended September 30, 2018 , except for the accounting policies for revenue recognition, trade receivables and deferred contract costs that were updated as a result of adopting Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) (“Topic 606”). For more information, refer to the “Recently Adopted Accounting Standards” and Note 2.
Recently Adopted Accounting Standards and Recent Accounting Standards Not Yet Effective	Recently Adopted Accounting Standards Financial Instruments – Recognition and Measurement In January 2016, the Financial Accounting Standard Board (“FASB”) issued ASU 2016-01—Financial Instruments—Overall (Subtopic 825-10): Recognition and Measurement of Financial Assets and Financial Liabilities, with further clarifications made recently with the issuance of ASU 2018-03, which requires most equity investments to be measured at fair value, with subsequent changes in fair value recognized in net income. A practicality exception applies to those equity investments that do not have a readily determinable fair value. These investments may be measured at cost, adjusted for changes in observable prices minus impairment. ASU 2016-01 was effective prospectively for us beginning on January 1, 2018 for our equity investments, which were previously accounted for under the cost-method. We adopted ASU 2016-01 on January 1, 2018. There was no material impact on our condensed consolidated financial statements as of the adoption date. Revenue Recognition In May 2014, the FASB issued Topic 606, which supersedes the revenue recognition requirements in Topic 605, Revenue Recognition, and requires entities to recognize revenue when control of the promised goods or services is transferred to customers at an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. We adopted Topic 606 as of January 1, 2018 using the modified retrospective transition method. The comparative information has not been restated and continues to be reported under the accounting standards in effect for those periods. We recorded a net reduction to our accumulated deficit as of January 1, 2018 of $ 117.3 million due to the cumulative impact of adopting Topic 606. The primary impact of adopting Topic 606 relates to the deferral of our incremental contract costs, which are comprised of sales commissions. Prior to January 1, 2018, we expensed all sales commissions upfront. Beginning on January 1, 2018, we continue to expense sales commissions related to product sales upfront, but capitalize and then amortize certain sales commissions on service contracts over the applicable amortization period. The capitalized sales commissions for initial service contracts are deferred and then amortized as expense on a straight-line basis over the period of benefit which we have determined to be five years. Sales commissions for renewal contracts are deferred and then amortized on a straight line basis over the contractual period of the underlying contracts. The deferral of sales commissions generated a deferred tax liability of $23.8 million , of which $18.0 million was recorded against deferred tax assets and the remaining $ 5.8 million was recorded in other long-term liabilities on our condensed consolidated balance sheet. The impact on deferred revenue as of January 1, 2018 was $4.1 million , which primarily relates to certain changes in revenue recognition on software license sales and the acceleration of revenue from U.S.-based channel partners which were previously deferred until the product was sold through. Beginning on January 1, 2018, our sales returns reserve is now included on the balance sheet in accrued liabilities and no longer as a reduction to our accounts receivable. See Note 2 for further details. The cumulative effects of the changes made to our January 1, 2018 condensed consolidated balance sheet for the adoption of Topic 606 were as follows (in millions): Balance at December 31, 2017 Adjustments due to Topic 606 Balance at January 1, 2018 Assets: Accounts receivable, net $ 348.2 $ 13.6 $ 361.8 Inventory $ 77.3 $ (0.1 ) $ 77.2 Deferred tax assets $ 146.9 $ (18.0 ) $ 128.9 Deferred contract costs $ — $ 137.1 $ 137.1 Liabilities: Accrued liabilities $ 50.0 $ 13.6 $ 63.6 Deferred revenue, current $ 793.8 $ 0.3 $ 794.1 Deferred revenue, non-current $ 542.5 $ (4.4 ) $ 538.1 Other liabilities, non-current $ 8.6 $ 5.8 $ 14.4 Stockholders’ equity: Accumulated deficit $ (319.6 ) $ 117.3 $ (202.3 ) Recent Accounting Standards Not Yet Effective Leases In February 2016, the FASB issued ASU 2016-02—Leases, which requires the recognition of right-of-use assets and lease liabilities on the consolidated balance sheet for substantially all leases. ASU 2016-02 includes a number of optional practical expedients that entities may elect to apply. ASU 2016-02 will also require significant additional disclosures about the amount, timing and uncertainty of cash flows from leases. In July 2018, the FASB issued ASU 2018-10—Codification Improvements to Topic 842, Leases, and ASU 2018-11 Leases (Topic 842) Targeted Improvements, which address questions about how to apply certain aspects of Accounting Standards Codification (“ASC”) 2016-02. The clarifications address the rate implicit in the lease, impairment of the net investment in the lease, lessee reassessment of lease classification, lessor reassessment of lease term and purchase options and variable payments that depend on an index or rate, and provide an alternative transition approach that allows companies to initially apply the new leases standard by recognizing a cumulative-effect adjustment on adoption date. ASC 2016-02 will be effective for us beginning on January 1, 2019, using a modified retrospective approach. Based on our current lease portfolio, we currently estimate the value of leased assets and liabilities that may be recognized on the consolidated balance sheet to be at least $45.0 million . We are continuing to evaluate the impact of ASU 2016-02 and our estimate is subject to change. We do not believe that ASC 2016-02 will have a material impact on our consolidated statements of operations and cash flows. We expect to expand our disclosures in the notes to consolidated financial statements to include more details on our leases, significant judgments and lease-related amounts recognized in the consolidated financial statements. Stock Compensation In June 2018, the FASB issued ASU 2018-07—Compensation—Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, which simplifies the accounting for share-based payments to nonemployees by aligning it with the accounting for share-based payments to employees subject to certain exceptions. ASC 2018-07 expands the scope of ASC Topic 718, Compensation-Stock Compensation (“ASC 718”) to include share-based payments granted to nonemployees in exchange for goods or services used or consumed in an entity’s own operations and supersedes the guidance in ASC 505-50 by moving it to ASC 718. This amendment is effective for us beginning January 1, 2019. Early adoption is permitted, but no earlier than an entity’s adoption date of ASC 606. We are currently evaluating the impact of ASU 2018-07 on our consolidated financial statements. Cloud Computing In August 2018, the FASB issued ASU 2018-15—Intangibles-Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer’s Accounting for Implementation Costs Incurred in a Cloud Computing Arrangement That Is a Service Contract, which requires a customer in a cloud computing arrangement that is a service contract to follow the internal-use software guidance in ASC Subtopic 350-40 to determine which implementation costs to capitalize as assets or expense as incurred. ASU 2018-15 is effective for us beginning January 1, 2020, and early adoption is permitted. We are currently evaluating the impact of ASU 2018-15 on our consolidated financial statements. Fair Value Measurements In August 2018, the FASB issued ASU 2018-13—Fair Value Measurement (Topic 820): Disclosure Framework—Changes to the Disclosure Requirements for Fair Value Measurement, which eliminates, adds and modifies certain disclosure requirements for fair value measurements in ASC 820—Fair Value Measurement as part of its disclosure framework project. ASU 2018-13 is effective for us beginning January 1, 2020. The amendments in ASU 2018-13 on changes in unrealized gains and losses, the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and the narrative description of measurement uncertainty should be applied prospectively for only the most recent interim or annual period presented in the initial fiscal year of adoption. All other amendments in ASU 2018-13 should be applied retrospectively to all periods presented upon their effective date. Early adoption is permitted upon issuance of ASU 2018-13. An entity is permitted to early adopt any removed or modified disclosures upon issuance of ASU 2018-13 and delay adoption of the additional disclosures until their effective date. We are currently evaluating the impact of ASU 2018-13 on our consolidated financial statements. Comprehensive Income In February 2018, the FASB issued ASU 2018-02—Income Statement-Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, which allows companies to reclassify stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017 (the “2017 Tax Act”), from accumulated other comprehensive income to retained earnings. ASU 2018-02 also requires certain new disclosures regardless of the election. ASU 2018-02 is effective for us beginning January 1, 2019, and early adoption is permitted. We are currently evaluating the impact of ASU 2018-02 on our consolidated financial statements. Financial Instruments In June 2016, the FASB issued ASU 2016-13—Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which requires a financial asset (or a group of financial assets) measured at an amortized cost basis to be presented at the net amount expected to be collected. The new approach to estimating credit losses (referred to as the current expected credit losses model) applies to most financial assets measured at amortized cost and certain other instruments, including trade and other receivables, loans and held-to-maturity debt securities. ASU 2016-13 is effective for us beginning on January 1, 2020, and early adoption is permitted. We are currently evaluating the impact of ASU 2016-13 on our consolidated financial statements.
Revenue Recognition	Revenue recognition On January 1, 2018 we adopted Topic 606 using the modified retrospective method applied to those contracts which were not completed as of January 1, 2018. Results for reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported under Topic 605. The details of significant changes and quantitative impact of the changes are discussed below. We derive the majority of our revenue from sales of our products, FortiGuard security subscription and FortiCare technical support services, and other services. Beginning in 2018, revenues are recognized when control of these goods or services is transferred to our customers, in an amount that reflects the consideration we expect to be entitled to in exchange for those goods or services. Prior to 2018, revenue was recognized under Topic 605 when all of the following criteria were met: (i) persuasive evidence of an arrangement existed, (ii) delivery has occurred or services have been rendered, (iii) sales price was fixed or determinable and (iv) collectability was reasonably assured. Under Topic 606, we determine revenue recognition through the following steps: • identification of the contract, or contracts, with the customer, • identification of the performance obligations in the contract, including evaluation of performance obligations as to being distinct goods or services in a contract, • determination of the transaction price, • allocation of the transaction price to the performance obligations in the contract, and • recognition of revenue when, or as, we satisfy a performance obligation. Product revenue primarily consists of sales of hardware and software licenses of our FortiGate and Fabric products. We derive a majority of product sales from our FortiGate products. Our FortiGate products include a broad set of built-in security and networking features and functionalities including firewall, SD-WAN, data leak prevention, VPN, switch and wireless controller and WAN acceleration, among others. We previously recognized product revenue for sales to distributors that had no general right of return and direct sales to end-customers upon shipment, based on general revenue recognition accounting guidance once all other revenue recognition criteria were met. Certain distributors are granted stock rotation rights, limited rights of return or rebates for sales of our products. The arrangement fee for this group of distributors was not fixed or determinable when products were shipped and revenue was therefore deferred and recognized upon sell-through. Under Topic 606, we recognize product revenue upon shipment when control of the promised goods is transferred to the customer. We recognize revenue from term licenses upon electronic transfer of the license key to the customer. Previously, term licenses were recognized over the license period. We generally provide a 1-year warranty on hardware products and a 90-day warranty on software that provides assurance that our hardware or software products conform to published specifications. Such assurance-type warranties are not deemed to be separate performance obligations from the hardware or software product and costs associated with providing the warranties are accrued in accordance with ASC 460-10. Service revenue relates to sales of our FortiGuard security subscription, FortiCare technical support services, and other services. Our FortiGuard security subscription services provide access to our application control, intrusion prevention, anti-botnet and mobile, anti-spam, web filtering, cloud sandbox and virus outbreak protection, industry security, security rating service and threat intelligent service functionality. Our FortiCare support services include rights to unspecified software upgrades, maintenance releases and patches, telephone and internet access to technical support personnel. Our typical subscription and contractual support term is one to three years, and to a lesser extent, five years. Our revenue recognition for service arrangements did not significantly change under Topic 606. We continue to recognize revenue from these services ratably over the contractual service period because of continuous transfer of control to the customer over the maintenance period. Revenue related to subsequent renewals of these services are recognized over the support term of the renewal agreement. We also generate a small portion of our revenue from other services consisting of professional services, training and software-as-a-service (“SaaS”) which is either hosted or cloud-based services. We recognize revenue from professional and training services as the services are provided. We recognize revenue from SaaS as the subscription service is delivered over the term, which is typically one year, or on a monthly usage basis. To date, SaaS revenue has not represented a significant percentage of our total revenue. Our sales contracts typically contain multiple deliverables, such as hardware, software license, security subscription, technical support services and other services, which are generally capable of being distinct and accounted for as separate performance obligations. We evaluated the criteria to be distinct under Topic 606 and concluded that the hardware and software license were distinct and distinct in the context of the contract from the security subscription and technical support services, as the customer can benefit from the hardware and license without the services and the services are separately identifiable within the contract. We allocate the transaction price to each performance obligation based on relative standalone selling price. We determine standalone selling price based on the historical pricing and discounting practices for those services when sold separately. We determine standalone selling price for a product or service by considering multiple historical factors including, but not limited to, cost of products, gross margin objectives, pricing practices, geographies and the term of the service contract that fall within a reasonably range as a percentage of list price. Revenue is reported net of sales tax. Under Topic 605, revenue from contracts that contain our products and services are allocated to each unit of accounting based on an estimated selling price using vendor-specific objective evidence (“VSOE”) of selling price, if it existed, or third-party evidence (“TPE”) of selling price. If neither VSOE nor TPE of selling price existed for a deliverable, we used our best estimate of selling price for that deliverable. For multiple-element arrangements where software deliverables were included, revenue was allocated to the non-software deliverables and to the software deliverables as a group using the relative estimated selling prices of each of the deliverables in the arrangement based on the estimated selling price hierarchy. The amount allocated to the software deliverables was then allocated to each software deliverable using the residual method when VSOE of fair value existed. If evidence of VSOE of fair value of one or more undelivered elements did not exist, all software allocated revenue was deferred and recognized when delivery of those elements occurred or when fair value was established. When the undelivered element for which we did not have VSOE of fair value was support, revenue for the entire arrangement was recognized ratably over the support period. The same residual method and VSOE of fair value principles applied for our multiple element arrangements that contained only software elements. In certain circumstances, our contracts include provisions for sales rebates and other customer incentive programs. Additionally, in limited circumstances, we may permit end-customers, distributors and resellers to return our products, subject to varying limitations, for a refund within a reasonably short period from the date of purchase. These amounts are accounted for as variable consideration that can decrease the transaction price. We estimate variable consideration at the most likely amounts to which we expect our customers to be entitled. We include estimated amounts in the transaction price to the extent that it is probable that a significant reversal of cumulative revenue recognized will not occur when the uncertainty associated with the variable consideration is resolved. Our estimate for sales return reserve was $13.7 million as of September 30, 2018 and is included in current liabilities in our condensed consolidated balance sheet. Under Topic 605, a sales return reserve of $13.6 million was presented as a reduction to accounts receivable as of December 31, 2017. We generally invoice at the time of our sale for the total price of the hardware, software licenses, security and technical support and other services, and the invoice is payable within 30 to 45 days. We also invoice certain services on a monthly basis. Amounts billed and due from our customers are classified as receivables on the balance sheet and do not bear interest. Our deferred revenue primarily consists of amounts that have been invoiced but have not been recognized as revenue as of period end. During the three and nine months ended September 30, 2018 , we recognized $ 173.0 million and $615.3 million , respectively, in revenue that was included in the deferred revenue balance as of December 31, 2017. Shipping and handling fees charged to our customers are recognized as product revenue in the period shipped and the related costs for providing these services are recorded as a cost of sale. Shipping and handling fees recognized as product revenue were not significant during the three and nine months ended September 30, 2018 and 2017.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Impact of Adopting New Accounting Pronouncement	The cumulative effects of the changes made to our January 1, 2018 condensed consolidated balance sheet for the adoption of Topic 606 were as follows (in millions): Balance at December 31, 2017 Adjustments due to Topic 606 Balance at January 1, 2018 Assets: Accounts receivable, net $ 348.2 $ 13.6 $ 361.8 Inventory $ 77.3 $ (0.1 ) $ 77.2 Deferred tax assets $ 146.9 $ (18.0 ) $ 128.9 Deferred contract costs $ — $ 137.1 $ 137.1 Liabilities: Accrued liabilities $ 50.0 $ 13.6 $ 63.6 Deferred revenue, current $ 793.8 $ 0.3 $ 794.1 Deferred revenue, non-current $ 542.5 $ (4.4 ) $ 538.1 Other liabilities, non-current $ 8.6 $ 5.8 $ 14.4 Stockholders’ equity: Accumulated deficit $ (319.6 ) $ 117.3 $ (202.3 ) The following tables summarize the impact of adopting Topic 606 on our condensed consolidated financial statements as of and for the three and nine months ended September 30, 2018 (in millions). These tables do not represent the full condensed consolidated financial statements as they only reflect the accounts impacted by the adoption of Topic 606. Condensed Consolidated Balance Sheet As of September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase (Decrease) Assets: Accounts receivable $ 324.4 $ 310.7 $ 13.7 Inventory $ 80.8 $ 81.9 $ (1.1 ) Deferred contract costs $ 169.6 $ — $ 169.6 Deferred tax assets $ 147.8 $ 175.6 $ (27.8 ) Liabilities: Accrued liabilities $ 60.7 $ 45.5 $ 15.2 Deferred revenue, current $ 876.2 $ 896.6 $ (20.4 ) Deferred revenue, non-current $ 668.2 $ 667.0 $ 1.2 Other liabilities, non-current $ 11.1 $ 5.2 $ 5.9 Stockholders’ Equity Accumulated deficit $ (156.0 ) $ (308.5 ) $ 152.5 Condensed Consolidated Statement of Operations Three Months Ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase (Decrease) REVENUE: Product (1) $ 164.5 $ 162.3 $ 2.2 Service 289.4 289.6 (0.2 ) Total revenue 453.9 451.9 2.0 COSTS OF REVENUE: Product 72.0 72.3 (0.3 ) GROSS PROFIT: Product 92.5 90.0 2.5 Service 249.8 250.0 (0.2 ) Total gross profit 342.3 340.0 2.3 OPERATING EXPENSES: Sales and marketing expenses 198.3 207.3 (9.0 ) OPERATING INCOME 62.8 51.5 11.3 INCOME BEFORE INCOME TAXES 70.6 59.3 11.3 PROVISION FOR INCOME TAXES 11.9 9.8 2.1 NET INCOME $ 58.7 $ 49.5 $ 9.2 Net income per share: Basic $ 0.35 $ 0.29 $ 0.05 Diluted $ 0.33 $ 0.28 $ 0.05 (1) Product revenue during the three months ended September 30, 2018 included a $2.2 million benefit from the adoption of Topic 606, which primarily related to the change in accounting treatment under Topic 606 for some of our software products where revenue from these arrangements is now recognized upfront instead of ratably over the contracted service term. Nine Months Ended September 30, 2018 As Reported Balances Without Adoption of Effect of Change REVENUE: Product (1) $ 473.6 $ 461.5 $ 12.1 Service 820.6 819.1 1.5 Total revenue 1,294.2 1,280.6 13.6 COST OF REVENUE: Product 204.1 203.1 1.0 GROSS PROFIT: Product 269.5 258.4 11.1 Service 702.8 701.3 1.5 Total gross profit 972.3 959.7 12.6 OPERATING EXPENSES Sales and marketing expenses 576.4 608.9 (32.5 ) OPERATING INCOME 145.9 100.8 45.1 INCOME BEFORE INCOME TAXES 158.8 113.7 45.1 BENEFIT FROM INCOME TAXES 9.2 (0.7 ) 9.9 NET INCOME $ 149.6 $ 114.4 $ 35.2 Net income per share: Basic $ 0.89 $ 0.68 $ 0.21 Diluted $ 0.86 $ 0.66 $ 0.20 (1) Product revenue during the nine months ended September 30, 2018 included a $12.1 million benefit from the adoption of Topic 606, which primarily related to the change in accounting treatment under Topic 606 for some of our software products where revenue from these arrangements is now recognized upfront instead of ratably over the contracted service term. Condensed Consolidated Statement of Cash Flows Nine Months Ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase (Decrease) Cash flows from operating activities: Net income $ 149.6 $ 114.4 $ 35.2 Adjustments to reconcile net income to net cash provided by operating activities: Amortization of deferred contract costs 66.3 — 66.3 Other (1.7 ) (1.6 ) (0.1 ) Changes in operating assets and liabilities: Inventory (19.0 ) (20.0 ) 1.0 Deferred contract costs (98.8 ) — (98.8 ) Deferred tax assets (19.1 ) (29.0 ) 9.9 Accrued liabilities (2.0 ) (3.5 ) 1.5 Deferred revenue 209.9 224.9 (15.0 ) Net cash provided by operating activities $ 458.7 $ 458.7 $ —

Revenue Recognition (Tables)

Revenue Recognition (Tables)	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	Disaggregation of Revenue The following table presents our revenue disaggregated by major product and service lines (in millions): Three Months Ended Nine Months Ended September 30, September 30, 2017 (1) September 30, September 30, 2017 (1) Product $ 164.5 $ 137.1 $ 473.6 $ 415.1 Service: Security subscription 157.0 130.8 440.7 366.3 Technical support 121.4 96.1 347.4 267.3 Professional services and training 11.0 10.2 32.5 29.6 Total service revenue 289.4 237.1 820.6 663.2 Total revenue $ 453.9 $ 374.2 $ 1,294.2 $ 1,078.3 (1) As noted above, prior period amounts have not been adjusted under the modified retrospective method.
Impact of Adopting New Accounting Pronouncement	The cumulative effects of the changes made to our January 1, 2018 condensed consolidated balance sheet for the adoption of Topic 606 were as follows (in millions): Balance at December 31, 2017 Adjustments due to Topic 606 Balance at January 1, 2018 Assets: Accounts receivable, net $ 348.2 $ 13.6 $ 361.8 Inventory $ 77.3 $ (0.1 ) $ 77.2 Deferred tax assets $ 146.9 $ (18.0 ) $ 128.9 Deferred contract costs $ — $ 137.1 $ 137.1 Liabilities: Accrued liabilities $ 50.0 $ 13.6 $ 63.6 Deferred revenue, current $ 793.8 $ 0.3 $ 794.1 Deferred revenue, non-current $ 542.5 $ (4.4 ) $ 538.1 Other liabilities, non-current $ 8.6 $ 5.8 $ 14.4 Stockholders’ equity: Accumulated deficit $ (319.6 ) $ 117.3 $ (202.3 ) The following tables summarize the impact of adopting Topic 606 on our condensed consolidated financial statements as of and for the three and nine months ended September 30, 2018 (in millions). These tables do not represent the full condensed consolidated financial statements as they only reflect the accounts impacted by the adoption of Topic 606. Condensed Consolidated Balance Sheet As of September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase (Decrease) Assets: Accounts receivable $ 324.4 $ 310.7 $ 13.7 Inventory $ 80.8 $ 81.9 $ (1.1 ) Deferred contract costs $ 169.6 $ — $ 169.6 Deferred tax assets $ 147.8 $ 175.6 $ (27.8 ) Liabilities: Accrued liabilities $ 60.7 $ 45.5 $ 15.2 Deferred revenue, current $ 876.2 $ 896.6 $ (20.4 ) Deferred revenue, non-current $ 668.2 $ 667.0 $ 1.2 Other liabilities, non-current $ 11.1 $ 5.2 $ 5.9 Stockholders’ Equity Accumulated deficit $ (156.0 ) $ (308.5 ) $ 152.5 Condensed Consolidated Statement of Operations Three Months Ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase (Decrease) REVENUE: Product (1) $ 164.5 $ 162.3 $ 2.2 Service 289.4 289.6 (0.2 ) Total revenue 453.9 451.9 2.0 COSTS OF REVENUE: Product 72.0 72.3 (0.3 ) GROSS PROFIT: Product 92.5 90.0 2.5 Service 249.8 250.0 (0.2 ) Total gross profit 342.3 340.0 2.3 OPERATING EXPENSES: Sales and marketing expenses 198.3 207.3 (9.0 ) OPERATING INCOME 62.8 51.5 11.3 INCOME BEFORE INCOME TAXES 70.6 59.3 11.3 PROVISION FOR INCOME TAXES 11.9 9.8 2.1 NET INCOME $ 58.7 $ 49.5 $ 9.2 Net income per share: Basic $ 0.35 $ 0.29 $ 0.05 Diluted $ 0.33 $ 0.28 $ 0.05 (1) Product revenue during the three months ended September 30, 2018 included a $2.2 million benefit from the adoption of Topic 606, which primarily related to the change in accounting treatment under Topic 606 for some of our software products where revenue from these arrangements is now recognized upfront instead of ratably over the contracted service term. Nine Months Ended September 30, 2018 As Reported Balances Without Adoption of Effect of Change REVENUE: Product (1) $ 473.6 $ 461.5 $ 12.1 Service 820.6 819.1 1.5 Total revenue 1,294.2 1,280.6 13.6 COST OF REVENUE: Product 204.1 203.1 1.0 GROSS PROFIT: Product 269.5 258.4 11.1 Service 702.8 701.3 1.5 Total gross profit 972.3 959.7 12.6 OPERATING EXPENSES Sales and marketing expenses 576.4 608.9 (32.5 ) OPERATING INCOME 145.9 100.8 45.1 INCOME BEFORE INCOME TAXES 158.8 113.7 45.1 BENEFIT FROM INCOME TAXES 9.2 (0.7 ) 9.9 NET INCOME $ 149.6 $ 114.4 $ 35.2 Net income per share: Basic $ 0.89 $ 0.68 $ 0.21 Diluted $ 0.86 $ 0.66 $ 0.20 (1) Product revenue during the nine months ended September 30, 2018 included a $12.1 million benefit from the adoption of Topic 606, which primarily related to the change in accounting treatment under Topic 606 for some of our software products where revenue from these arrangements is now recognized upfront instead of ratably over the contracted service term. Condensed Consolidated Statement of Cash Flows Nine Months Ended September 30, 2018 As Reported Balances Without Adoption of Topic 606 Effect of Change Increase (Decrease) Cash flows from operating activities: Net income $ 149.6 $ 114.4 $ 35.2 Adjustments to reconcile net income to net cash provided by operating activities: Amortization of deferred contract costs 66.3 — 66.3 Other (1.7 ) (1.6 ) (0.1 ) Changes in operating assets and liabilities: Inventory (19.0 ) (20.0 ) 1.0 Deferred contract costs (98.8 ) — (98.8 ) Deferred tax assets (19.1 ) (29.0 ) 9.9 Accrued liabilities (2.0 ) (3.5 ) 1.5 Deferred revenue 209.9 224.9 (15.0 ) Net cash provided by operating activities $ 458.7 $ 458.7 $ —

Financial Instruments and Fai_2

Financial Instruments and Fair Value (Tables)	9 Months Ended
	Sep. 30, 2018
Financial Instruments and Fair Value [Abstract]
Summary of Investments	The following tables summarize our investments (in millions): September 30, 2018 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate debt securities $ 296.6 $ — $ (1.2 ) $ 295.4 Certificates of deposit and term deposits (1) 106.1 — — 106.1 Commercial paper 72.5 — (0.1 ) 72.4 U.S. government and agency securities 29.7 — (0.1 ) 29.6 Total available-for-sale securities $ 504.9 $ — $ (1.4 ) $ 503.5 December 31, 2017 Amortized Cost Unrealized Gains Unrealized Losses Fair Value Corporate debt securities $ 391.0 $ — $ (1.2 ) $ 389.8 Commercial paper 74.2 — — 74.2 Certificates of deposit and term deposits (1) 45.9 — — 45.9 U.S. government and agency securities 28.5 — (0.1 ) 28.4 Total available-for-sale securities $ 539.6 $ — $ (1.3 ) $ 538.3 (1) The majority of our certificates of deposit and term deposits are foreign deposits.
Schedule of Unrealized Loss on Investments	The following tables show the gross unrealized losses and the related fair values of our investments that have been in a continuous unrealized loss position (in millions): September 30, 2018 Less Than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate debt securities $ 163.1 $ (0.3 ) $ 94.5 $ (0.9 ) $ 257.6 $ (1.2 ) Commercial paper 90.5 (0.1 ) — — 90.5 (0.1 ) Certificates of deposit and term deposits 35.9 — — — 35.9 — U.S. government and agency securities 26.2 — 3.5 (0.1 ) 29.7 (0.1 ) Total available-for-sale securities $ 315.7 $ (0.4 ) $ 98.0 $ (1.0 ) $ 413.7 $ (1.4 ) December 31, 2017 Less Than 12 Months 12 Months or Greater Total Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses Corporate debt securities $ 317.4 $ (0.9 ) $ 58.2 $ (0.3 ) $ 375.6 $ (1.2 ) Certificates of deposit and term deposits 37.2 — — — 37.2 — Commercial paper 29.0 — — — 29.0 — U.S. government and agency securities 17.0 — 11.4 (0.1 ) 28.4 (0.1 ) Total available-for-sale securities $ 400.7 $ (0.9 ) $ 69.6 $ (0.4 ) $ 470.3 $ (1.3 )
Investments Classified by Contractual Maturity Date	The contractual maturities of our investments were as follows (in millions): September 30, December 31, Due within one year $ 464.9 $ 440.3 Due within one to three years 38.6 98.0 Total $ 503.5 $ 538.3
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis	The following tables present the fair value of our financial assets measured at fair value on a recurring basis as of September 30, 2018 and December 31, 2017 (in millions): September 30, 2018 December 31, 2017 Aggregate Fair Value Quoted Prices in Active Markets For Identical Assets Significant Other Observable Remaining Inputs Significant Other Unobservable Remaining Inputs Aggregate Fair Value Quoted Prices in Active Markets For Identical Assets Significant Other Observable Remaining Inputs Significant Other Unobservable Remaining Inputs (Level 1) (Level 2) (Level 3) (Level 1) (Level 2) (Level 3) Assets: Corporate debt securities $ 295.4 $ — $ 295.4 $ — $ 411.1 $ — $ 411.1 $ — Certificates of deposit and term deposits 228.3 — 228.3 — 132.1 — 132.1 — Money market funds 139.0 139.0 — — 195.6 195.6 — — Commercial paper 121.0 — 121.0 — 128.9 — 128.9 — U.S. government and agency securities 29.6 26.1 3.5 — 28.4 24.9 3.5 — Total $ 813.3 $ 165.1 $ 648.2 $ — $ 896.1 $ 220.5 $ 675.6 $ — Reported as: Cash equivalents $ 309.8 $ 357.8 Short-term investments 464.9 440.3 Long-term investments 38.6 98.0 Total $ 813.3 $ 896.1

Inventory (Tables)

Inventory (Tables)	9 Months Ended
	Sep. 30, 2018
Inventory Disclosure [Abstract]
Inventory	Inventory consisted of the following (in millions): September 30, December 31, Raw materials $ 12.5 $ 13.0 Finished goods 68.3 64.3 Inventory $ 80.8 $ 77.3

Property and Equipment_Net (Tab

Property and Equipment—Net (Tables)	9 Months Ended
	Sep. 30, 2018
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment - Net	Property and equipment—net consisted of the following (in millions): September 30, December 31, Building and building improvements $ 138.6 $ 133.2 Computer equipment and software 95.0 79.9 Land 75.7 65.6 Leasehold improvements 21.9 20.8 Evaluation units 20.2 20.1 Furniture and fixtures 16.7 14.7 Construction-in-progress 11.5 6.3 Total property and equipment 379.6 340.6 Less: accumulated depreciation (114.2 ) (95.2 ) Property and equipment—net $ 265.4 $ 245.4

Goodwill and Other Intangible_2

Goodwill and Other Intangible Assets - Net (Tables)	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Changes in Carrying Value of Goodwill	Changes in the carrying value of goodwill were (in millions): Amount Balance—December 31, 2017 $ 14.6 Addition due to business combination 11.1 Balance—September 30, 2018 $ 25.7
Schedule of Finite-Lived and Indefinite-Lived Intangible Assets by Major Class	The following tables present other intangible assets—net as of September 30, 2018 and December 31, 2017 (in millions, except years): September 30, 2018 Weighted-Average Useful Life (in Years) Gross Accumulated Amortization Net Other intangible assets—net: Finite-lived intangible assets: Developed technologies and other 3.8 $ 31.4 $ 18.1 $ 13.3 Customer relationships 4.5 16.7 11.9 4.8 Total other intangible assets—net $ 48.1 $ 30.0 $ 18.1 The following tables present other intangible assets—net as of September 30, 2018 and December 31, 2017 (in millions, except years): September 30, 2018 Weighted-Average Useful Life (in Years) Gross Accumulated Amortization Net Other intangible assets—net: Finite-lived intangible assets: Developed technologies and other 3.8 $ 31.4 $ 18.1 $ 13.3 Customer relationships 4.5 16.7 11.9 4.8 Total other intangible assets—net $ 48.1 $ 30.0 $ 18.1 December 31, 2017 Weighted-Average Useful Life (in Years) Gross Accumulated Amortization Net Other intangible assets—net: Finite-lived intangible assets: Developed technologies and other 3.8 $ 24.0 $ 13.7 $ 10.3 Customer relationships 4.7 14.5 10.1 4.4 38.5 23.8 14.7 Indefinite-lived intangible assets: In-process research and development 1.6 — 1.6 Total other intangible assets—net $ 40.1 $ 23.8 $ 16.3
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense	The following table summarizes estimated future amortization expense of finite-lived intangible assets—net (in millions): Amount Years: 2018 $ 2.5 2019 8.2 2020 4.6 2021 and thereafter 2.8 Total $ 18.1

Net Income Per Share (Tables)

Net Income Per Share (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted	A reconciliation of the numerator and denominator used in the calculation of basic and diluted net income per share is as follows (in millions, except per share amounts): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Numerator: Net income $ 58.7 $ 26.7 $ 149.6 $ 60.4 Denominator: Basic shares: Weighted-average common stock outstanding-basic 169.8 175.5 168.7 175.3 Diluted shares: Weighted-average common stock outstanding-basic 169.8 175.5 168.7 175.3 Effect of potentially dilutive securities: RSUs 4.2 2.1 3.5 2.2 Stock options 1.6 1.3 1.4 1.4 ESPP 0.1 0.1 0.1 0.1 Weighted-average shares used to compute diluted net income per share 175.7 179.0 173.7 179.0 Net income per share: Basic $ 0.35 $ 0.15 $ 0.89 $ 0.34 Diluted $ 0.33 $ 0.15 $ 0.86 $ 0.34
Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share	The following weighted-average shares of common stock were excluded from the computation of diluted net income per share for the periods presented, as their effect would have been antidilutive (in millions): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, RSUs 0.3 1.0 0.6 1.6 Stock options — 1.1 0.4 1.1 ESPP 0.2 0.4 0.1 0.2 Total 0.5 2.5 1.1 2.9

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Contractual Obligation, Fiscal Year Maturity Schedule	The following table summarizes our future principal contractual obligations as of September 30, 2018 (in millions): Total 2018 2019 2020 2021 2022 Thereafter Operating lease commitments $ 52.0 $ 4.1 $ 15.3 $ 11.6 $ 8.0 $ 5.0 $ 8.0 Inventory purchase commitments 174.0 111.1 58.7 4.2 — — — Total $ 226.0 $ 115.2 $ 74.0 $ 15.8 $ 8.0 $ 5.0 $ 8.0

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Compensation, Restricted Stock Units Award Activity	The following table summarizes the activity and related information for RSUs for the periods presented below (in millions, except per share amounts): Restricted Stock Units Outstanding Number of Shares Weighted-Average Grant Date Fair Value per Share Balance—December 31, 2017 8.5 $ 34.79 Granted 3.7 54.82 Forfeited (0.7 ) 38.24 Vested (3.1 ) 34.32 Balance—September 30, 2018 8.4 $ 44.48
Schedule of Share-based Compensation, Shares Withheld for Taxes	The following summarizes the number and value of the shares withheld for employee taxes (in millions): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Shares withheld for taxes 0.2 0.3 0.9 1.0 Amount withheld for taxes $ 15.5 $ 10.0 $ 48.0 $ 35.9
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	The following table summarizes the weighted-average assumptions relating to our employee stock options: Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Expected term in years 4.4 4.4 4.4 4.4 Volatility 30.5 % 33.1 % 31.6 % 36.1 % Risk-free interest rate 2.7 % 1.8 % 2.7 % 1.9 % Dividend rate — % — % — % — %
Schedule of Share-based Compensation, Stock Options, Activity	The following table summarizes the stock option activity and related information for the periods presented below (in millions, except exercise prices and contractual life): Options Outstanding Number of Shares Weighted- Average Exercise Price Weighted- Average Remaining Contractual Life (Years) Aggregate Intrinsic Value Balance—December 31, 2017 4.3 $ 27.50 Granted 0.8 51.29 Forfeited (0.1 ) 31.90 Exercised (1.8 ) 24.74 Balance—September 30, 2018 3.2 $ 34.69 Options vested and expected to vest—September 30, 2018 3.2 $ 34.69 4.13 $ 183.4 Options exercisable—September 30, 2018 1.6 $ 28.42 2.75 $ 104.9
Schedule of Share-based Compensation, Stock Options, Activity, Additional Information	Additional information related to our stock options is summarized below (in millions, except per share amounts): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Weighted-average fair value per share granted $ 22.75 $ 11.09 $ 15.67 $ 12.17 Intrinsic value of options exercised 14.1 3.4 53.6 30.3 Fair value of options vested 1.4 1.6 5.7 6.7
Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions	In determining the fair value of the ESPP, we use the Black-Scholes option pricing model that employs the following weighted-average assumptions: Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Expected term in years 0.5 0.5 0.5 0.5 Volatility 30.5 % 26.2 % 28.9 % 29.5 % Risk-free interest rate 2.2 % 1.2 % 2.0 % 0.9 % Dividend rate — % — % — % — %
Schedule of Share-based Payment Award Employee Stock Purchase Plan Additional Information	Additional information related to the ESPP is provided below (in millions, except per share amounts): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Weighted-average fair value per share granted $ 18.28 $ 8.31 $ 14.14 $ 8.73 Shares issued under the ESPP 0.4 0.5 1.1 1.1 Weighted-average price per share issued $ 41.89 $ 31.49 $ 35.32 $ 29.52
Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs	Stock-based compensation expense is included in costs and expenses as follows (in millions): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Cost of product revenue $ 0.3 $ 0.3 $ 1.1 $ 1.0 Cost of service revenue 2.8 2.4 8.0 7.2 Research and development 9.3 8.0 26.9 24.1 Sales and marketing 26.0 19.6 70.5 58.4 General and administrative 4.8 4.0 13.8 12.0 Total stock-based compensation expense $ 43.2 $ 34.3 $ 120.3 $ 102.7
Schedule of Employee Service Share based Compensation Allocation of Recognized Period Costs by Award Type	The following table summarizes stock-based compensation expense by award type (in millions): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, RSUs $ 38.2 $ 29.9 $ 106.1 $ 89.8 Stock options 2.4 1.8 6.7 5.6 ESPP 2.6 2.6 7.5 7.3 Total stock-based compensation expense $ 43.2 $ 34.3 $ 120.3 $ 102.7
Income Tax Benefit from Stock Option Plans	Total income tax benefit associated with stock-based compensation that is recognized in the consolidated statements of operations is as follows (in millions): Three Months Ended Nine Months Ended September 30, September 30, September 30, September 30, Income tax benefit associated with stock-based compensation $ 6.8 $ 6.7 $ 19.0 $ 21.1

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2018
Segment Reporting [Abstract]
Revenue from external customers by geographic region	Three Months Ended Nine Months Ended Revenue September 30, September 30, September 30, September 30, Americas: United States $ 146.8 $ 123.7 $ 425.3 $ 367.1 Latin America (“LATAM”) 31.2 24.4 86.4 64.6 Canada 16.0 13.1 47.4 36.6 Total Americas 194.0 161.2 559.1 468.3 Europe, Middle East and Africa (“EMEA”) 165.4 138.3 474.3 394.2 Asia Pacific (“APAC”) 94.5 74.7 260.8 215.8 Total revenue $ 453.9 $ 374.2 $ 1,294.2 $ 1,078.3
Property and equipment by geographic region	Property and Equipment — net September 30, December 31, Americas: United States $ 127.8 $ 115.6 Canada 111.1 103.8 LATAM 0.4 0.3 Total Americas 239.3 219.7 EMEA: France 13.3 11.9 Other EMEA 3.5 5.8 Total EMEA 16.8 17.7 APAC 9.3 8.0 Total property and equipment—net $ 265.4 $ 245.4
Schedule of customer concentration	The following customers, each of which is a distributor, accounted for 10% or more of our revenue: Three Months Ended Nine Months Ended September 30, 2018 (1) September 30, September 30, 2018 (1) September 30, Exclusive Networks Group 29 % 29 % 29 % 23 % Ingram Micro 11 % 11 % 10 % 10 % (1) Due to the acquisition by Exclusive Networks Group of the U.S. division of Fine Tec Computers (“Fine Tec U.S.”) in July 2017, Fine Tec U.S.’s revenue and accounts receivable have been combined with Exclusive Networks Group. The following customer, which is a distributor, accounted for 10% or more of net accounts receivable: September 30, December 31, Exclusive Networks Group 33 % 35 % Ingram Micro 10 % * * Represents less than 10%

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Loss (Tables)	9 Months Ended
	Sep. 30, 2018
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Accumulated Other Comprehensive (Loss) Income	The following table summarizes the changes in accumulated balances of other comprehensive loss (in millions): Unrealized Losses on Investments Tax provision related to unrealized gains or losses on investments Total Balance—December 31, 2017 $ (1.3 ) $ 0.5 $ (0.8 ) Other comprehensive loss before reclassifications (0.1 ) (0.1 ) (0.2 ) Amounts reclassified from accumulated other comprehensive loss — — — Net current-period other comprehensive loss (0.1 ) (0.1 ) (0.2 ) Balance—September 30, 2018 $ (1.4 ) $ 0.4 $ (1.0 )

Summary of Significant Accoun_4

Summary of Significant Accounting Policies , Recent Accounting Pronouncements (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Dec. 31, 2019	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncement, Early Adoption [Line Items]
Accounts receivable—Net	$ 324.4			$ 348.2
Inventory	80.8			77.3
Deferred tax assets	147.8			146.9
Deferred contract costs	169.6			0
Accrued liabilities	60.7			50
Deferred revenue	876.2			793.8
DEFERRED REVENUE	668.2			542.5
OTHER LIABILITIES	11.1			8.6
Retained earnings	$ (156)			(319.6)
ASU 2014-09
New Accounting Pronouncement, Early Adoption [Line Items]
Accounts receivable—Net			$ 361.8
Inventory			77.2
Deferred tax assets			128.9
Deferred contract costs			137.1
Accrued liabilities			63.6
Deferred revenue			794.1
DEFERRED REVENUE			538.1
OTHER LIABILITIES			14.4
Retained earnings			(202.3)
Deferred tax liability			23.8
Maximum [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Revenue recognition period (in years)	5 years
Minimum [Member]
New Accounting Pronouncement, Early Adoption [Line Items]
Revenue recognition period (in years)	3 years
Minimum [Member] | Scenario, Forecast [Member] | ASU 2016-02
New Accounting Pronouncement, Early Adoption [Line Items]
Expected increase to assets and liabilities upon adoption of new accounting pronouncement		$ 45
Deferred Tax Asset [Member] | ASU 2014-09
New Accounting Pronouncement, Early Adoption [Line Items]
Deferred tax liability			18
Effect of Change Increase (Decrease) | ASU 2014-09
New Accounting Pronouncement, Early Adoption [Line Items]
Accounts receivable—Net	$ 13.7		13.6
Inventory	(1.1)		(0.1)
Deferred tax assets	(27.8)		(18)
Deferred contract costs	169.6		137.1
Accrued liabilities	15.2		13.6
Deferred revenue	(20.4)		0.3
DEFERRED REVENUE	1.2		(4.4)
OTHER LIABILITIES	5.9
Retained earnings	152.5		117.3
Deferred Revenue			4.1
Effect of Change Increase (Decrease) | Other Noncurrent Liabilities [Member] | ASU 2014-09
New Accounting Pronouncement, Early Adoption [Line Items]
OTHER LIABILITIES			$ 5.8
Balances Without Adoption of Topic 606
New Accounting Pronouncement, Early Adoption [Line Items]
Accounts receivable—Net				348.2
Inventory				77.3
Deferred tax assets				146.9
Deferred contract costs				0
Accrued liabilities				50
Deferred revenue				793.8
DEFERRED REVENUE				542.5
OTHER LIABILITIES				8.6
Retained earnings				$ (319.6)
Balances Without Adoption of Topic 606 | ASU 2014-09
New Accounting Pronouncement, Early Adoption [Line Items]
Accounts receivable—Net	310.7
Inventory	81.9
Deferred tax assets	175.6
Deferred contract costs	0
Accrued liabilities	45.5
Deferred revenue	896.6
DEFERRED REVENUE	667
OTHER LIABILITIES	5.2
Retained earnings	$ (308.5)

Revenue Recognition (Details)

Revenue Recognition (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Jan. 01, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Reserves for sales returns		$ 13,700,000
Accounts receivable	$ 324,400,000	324,400,000			$ 348,200,000
Deferred revenue recognized in period	173,000,000	615,300,000
Remaining performance obligation	1,540,000,000	1,540,000,000
Allowance for doubtful accounts	700,000	700,000			900,000
Sales return reserve					$ 13,600,000
Amortization of deferred contract costs	23,200,000	$ 66,300,000	$ 0
Impairment loss	0
Sales Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenue recognition period (in years)		3 years
Minimum [Member]
Disaggregation of Revenue [Line Items]
Revenue recognition period (in years)		3 years
Minimum [Member] | Sales Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenue recognition period (in years)		1 year
Maximum [Member]
Disaggregation of Revenue [Line Items]
Revenue recognition period (in years)		5 years
Maximum [Member] | Sales Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenue recognition period (in years)		5 years
ASU 2014-09
Disaggregation of Revenue [Line Items]
Accounts receivable				$ 361,800,000
ASU 2014-09 | Effect of Change Increase (Decrease)
Disaggregation of Revenue [Line Items]
Accounts receivable	$ 13,700,000	$ 13,700,000		$ 13,600,000
Amortization of deferred contract costs		$ 66,300,000

Revenue Recognition - Performan

Revenue Recognition - Performance Obligation Satisfaction Period (Details)	9 Months Ended
	Sep. 30, 2018
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation expected to be satisfied (percent)	80.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation expected to be satisfied (percent)	20.00%
Maximum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue recognition period (in years)	5 years
Maximum [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation expected recognition period for three-fourths of remaining obligation	2 years
Maximum [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation expected recognition period for three-fourths of remaining obligation	3 years
Minimum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue recognition period (in years)	3 years
Minimum [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation expected recognition period for three-fourths of remaining obligation	1 year
Minimum [Member] | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Performance obligation expected recognition period for three-fourths of remaining obligation	1 year

Revenue Recognition - Disaggreg

Revenue Recognition - Disaggregated Revenues (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Product	$ 164.5	$ 137.1	$ 473.6	$ 415.1
Service	289.4	237.1	820.6	663.2
Total revenue	453.9	374.2	1,294.2	1,078.3
Security Subscription [Member]
Disaggregation of Revenue [Line Items]
Service	157	130.8	440.7	366.3
Technical Support [Member]
Disaggregation of Revenue [Line Items]
Service	121.4	96.1	347.4	267.3
Professional Services and Training [Member]
Disaggregation of Revenue [Line Items]
Service	$ 11	$ 10.2	$ 32.5	$ 29.6

Revenue Recognition - Balance S

Revenue Recognition - Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Accounts receivable—Net	$ 324.4		$ 348.2
Inventory	80.8		77.3
Deferred contract costs	169.6		0
DEFERRED TAX ASSETS	147.8		146.9
Accrued liabilities	60.7		50
Deferred revenue	876.2		793.8
DEFERRED REVENUE	668.2		542.5
OTHER LIABILITIES	11.1		8.6
Accumulated deficit	(156)		(319.6)
ASU 2014-09
Disaggregation of Revenue [Line Items]
Accounts receivable—Net		$ 361.8
Inventory		77.2
Deferred contract costs		137.1
DEFERRED TAX ASSETS		128.9
Accrued liabilities		63.6
Deferred revenue		794.1
DEFERRED REVENUE		538.1
OTHER LIABILITIES		14.4
Accumulated deficit		(202.3)
Balances Without Adoption of Topic 606
Disaggregation of Revenue [Line Items]
Accounts receivable—Net			348.2
Inventory			77.3
Deferred contract costs			0
DEFERRED TAX ASSETS			146.9
Accrued liabilities			50
Deferred revenue			793.8
DEFERRED REVENUE			542.5
OTHER LIABILITIES			8.6
Accumulated deficit			$ (319.6)
Balances Without Adoption of Topic 606 | ASU 2014-09
Disaggregation of Revenue [Line Items]
Accounts receivable—Net	310.7
Inventory	81.9
Deferred contract costs	0
DEFERRED TAX ASSETS	175.6
Accrued liabilities	45.5
Deferred revenue	896.6
DEFERRED REVENUE	667
OTHER LIABILITIES	5.2
Accumulated deficit	(308.5)
Effect of Change Increase (Decrease) | ASU 2014-09
Disaggregation of Revenue [Line Items]
Accounts receivable—Net	13.7	13.6
Inventory	(1.1)	(0.1)
Deferred contract costs	169.6	137.1
DEFERRED TAX ASSETS	(27.8)	(18)
Accrued liabilities	15.2	13.6
Deferred revenue	(20.4)	0.3
DEFERRED REVENUE	1.2	(4.4)
OTHER LIABILITIES	5.9
Accumulated deficit	$ 152.5	$ 117.3

Revenue Recognition - Income St

Revenue Recognition - Income Statement (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
REVENUE:
Product	$ 164.5	$ 137.1	$ 473.6	$ 415.1
Service	289.4	237.1	820.6	663.2
Total revenue	453.9	374.2	1,294.2	1,078.3
COST OF REVENUE:
Product	72	58.1	204.1	174.2
GROSS PROFIT:
Product	92.5	79	269.5	240.9
Service	249.8	201.6	702.8	557.5
Total gross profit	342.3	280.6	972.3	798.4
OPERATING EXPENSES:
Sales and marketing	198.3	172.4	576.4	509.1
OPERATING INCOME	62.8	33.7	145.9	67.6
INCOME BEFORE INCOME TAXES	70.6	38	158.8	79
PROVISION FOR INCOME TAXES	11.9	11.3	9.2	18.6
NET INCOME	$ 58.7	$ 26.7	$ 149.6	$ 60.4
Net income per share (Note 9):
Basic (in dollars per share)	$ 0.35	$ 0.15	$ 0.89	$ 0.34
Diluted (in dollars per share)	$ 0.33	$ 0.15	$ 0.86	$ 0.34
ASU 2014-09 | Balances Without Adoption of Topic 606
REVENUE:
Product	$ 162.3		$ 461.5
Service	289.6		819.1
Total revenue	451.9		1,280.6
COST OF REVENUE:
Product	72.3		203.1
GROSS PROFIT:
Product	90		258.4
Service	250		701.3
Total gross profit	340		959.7
OPERATING EXPENSES:
Sales and marketing	207.3		608.9
OPERATING INCOME	51.5		100.8
INCOME BEFORE INCOME TAXES	59.3		113.7
PROVISION FOR INCOME TAXES	9.8		(0.7)
NET INCOME	$ 49.5		$ 114.4
Net income per share (Note 9):
Basic (in dollars per share)	$ 0.29		$ 0.68
Diluted (in dollars per share)	$ 0.28		$ 0.66
ASU 2014-09 | Effect of Change Increase (Decrease)
REVENUE:
Product	$ 2.2		$ 12.1
Service	(0.2)		1.5
Total revenue	2		13.6
COST OF REVENUE:
Product	(0.3)		1
GROSS PROFIT:
Product	2.5		11.1
Service	(0.2)		1.5
Total gross profit	2.3		12.6
OPERATING EXPENSES:
Sales and marketing	(9)		(32.5)
OPERATING INCOME	11.3		45.1
INCOME BEFORE INCOME TAXES	11.3		45.1
PROVISION FOR INCOME TAXES	2.1		9.9
NET INCOME	$ 9.2		$ 35.2
Net income per share (Note 9):
Basic (in dollars per share)	$ 0.05		$ 0.21
Diluted (in dollars per share)	$ 0.05		$ 0.20

Revenue Recognition - Cash Flow

Revenue Recognition - Cash Flow Statement (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Net income	$ 58.7	$ 26.7	$ 149.6	$ 60.4
Amortization of deferred contract costs	23.2		66.3	0
Other			(1.7)	3.2
Inventory			(19)	17.7
Prepaid expenses and other current assets			1.8	(9.6)
Deferred contract costs			(98.8)	0
Deferred tax assets			(19.1)	(22.1)
Accrued liabilities			(2)	8
Deferred revenue			209.9	184.4
Net cash provided by operating activities			458.7	$ 436.9
Balances Without Adoption of Topic 606 | ASU 2014-09
Disaggregation of Revenue [Line Items]
Net income	49.5		114.4
Amortization of deferred contract costs			0
Other			(1.6)
Inventory			(20)
Deferred contract costs			0
Deferred tax assets			(29)
Accrued liabilities			(3.5)
Deferred revenue			224.9
Net cash provided by operating activities			458.7
Effect of Change Increase (Decrease) | ASU 2014-09
Disaggregation of Revenue [Line Items]
Net income	$ 9.2		35.2
Amortization of deferred contract costs			66.3
Other			(0.1)
Inventory			1
Deferred contract costs			(98.8)
Deferred tax assets			9.9
Accrued liabilities			1.5
Deferred revenue			(15)
Net cash provided by operating activities			$ 0

Financial Instruments and Fai_3

Financial Instruments and Fair Value , Investments (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 504.9	$ 539.6
Unrealized Gains	0	0
Unrealized Losses	(1.4)	(1.3)
Fair Value	503.5	538.3
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	315.7	400.7
Less Than 12 Months, Unrealized Losses	(0.4)	(0.9)
12 Months or Greater, Fair Value	98	69.6
12 Months or Greater, Unrealized Losses	(1)	(0.4)
Total, Fair Value	413.7	470.3
Total, Unrealized Losses	(1.4)	(1.3)
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Due within one year	464.9	440.3
Due within one to three years	38.6	98
Fair Value	503.5	538.3
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	296.6	391
Unrealized Gains	0	0
Unrealized Losses	(1.2)	(1.2)
Fair Value	295.4	389.8
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	163.1	317.4
Less Than 12 Months, Unrealized Losses	(0.3)	(0.9)
12 Months or Greater, Fair Value	94.5	58.2
12 Months or Greater, Unrealized Losses	(0.9)	(0.3)
Total, Fair Value	257.6	375.6
Total, Unrealized Losses	(1.2)	(1.2)
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Fair Value	295.4	389.8
Certificates of deposit and term deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	106.1	45.9
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	106.1	45.9
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	35.9	37.2
Less Than 12 Months, Unrealized Losses	0	0
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total, Fair Value	35.9	37.2
Total, Unrealized Losses	0	0
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Fair Value	106.1	45.9
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	72.5	74.2
Unrealized Gains	0	0
Unrealized Losses	(0.1)	0
Fair Value	72.4	74.2
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	90.5	29
Less Than 12 Months, Unrealized Losses	(0.1)	0
12 Months or Greater, Fair Value	0	0
12 Months or Greater, Unrealized Losses	0	0
Total, Fair Value	90.5	29
Total, Unrealized Losses	(0.1)	0
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Fair Value	72.4	74.2
U.S. government and agency securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	29.7	28.5
Unrealized Gains	0	0
Unrealized Losses	(0.1)	(0.1)
Fair Value	29.6	28.4
Available-for-sale Securities, Continuous Unrealized Loss Position [Abstract]
Less Than 12 Months, Fair Value	26.2	17
Less Than 12 Months, Unrealized Losses	0	0
12 Months or Greater, Fair Value	3.5	11.4
12 Months or Greater, Unrealized Losses	(0.1)	(0.1)
Total, Fair Value	29.7	28.4
Total, Unrealized Losses	(0.1)	(0.1)
Available-for-sale Securities, Debt Maturities, Fair Value [Abstract]
Fair Value	$ 29.6	$ 28.4

Financial Instruments and Fai_4

Financial Instruments and Fair Value , Fair Value Measurements (Details) - Recurring Basis [Member] - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets, Fair Value Disclosure	$ 813.3	$ 896.1
Fair Value [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets, Fair Value Disclosure	165.1	220.5
Fair Value [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets, Fair Value Disclosure	648.2	675.6
Fair Value [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets, Fair Value Disclosure	0	0
Fair Value [Member] | Corporate debt securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	295.4	411.1
Fair Value [Member] | Corporate debt securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	0	0
Fair Value [Member] | Corporate debt securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	295.4	411.1
Fair Value [Member] | Corporate debt securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	0	0
Fair Value [Member] | Certificates of deposit and term deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	228.3	132.1
Fair Value [Member] | Certificates of deposit and term deposits [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	0	0
Fair Value [Member] | Certificates of deposit and term deposits [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	228.3	132.1
Fair Value [Member] | Certificates of deposit and term deposits [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	0	0
Fair Value [Member] | Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	139	195.6
Fair Value [Member] | Money market funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	139	195.6
Fair Value [Member] | Money market funds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	0	0
Fair Value [Member] | Money market funds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	0	0
Fair Value [Member] | Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	121	128.9
Fair Value [Member] | Commercial paper [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	0	0
Fair Value [Member] | Commercial paper [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	121	128.9
Fair Value [Member] | Commercial paper [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	0	0
Fair Value [Member] | U.S. government and agency securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	29.6	28.4
Fair Value [Member] | U.S. government and agency securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	26.1	24.9
Fair Value [Member] | U.S. government and agency securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	3.5	3.5
Fair Value [Member] | U.S. government and agency securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	0	0
Reported as [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total Assets, Fair Value Disclosure	813.3	896.1
Reported as [Member] | Cash equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	309.8	357.8
Reported as [Member] | Short-term investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	464.9	440.3
Reported as [Member] | Long-term investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities, Fair Value Disclosure	$ 38.6	$ 98

Inventory (Details)

Inventory (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Inventory, Net [Abstract]
Raw materials	$ 12.5	$ 13
Finished goods	68.3	64.3
Inventory	80.8	77.3
Materials at contract manufacturers	$ 2.9	2.6
Finished goods inventory held by distributors
Inventory, Net [Abstract]
Finished goods		$ 0.1

Property and Equipment_Net (Det

Property and Equipment—Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Property, Plant and Equipment, Net, by Type [Abstract]
Total property and equipment	$ 379.6		$ 379.6		$ 340.6
Less: accumulated depreciation	(114.2)		(114.2)		(95.2)
Property and equipment - net	265.4		265.4		245.4
Depreciation expense	11.8	$ 11.7	34.9	$ 34.7
Building and building improvements [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total property and equipment	138.6		138.6		133.2
Computer equipment and software [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total property and equipment	95		95		79.9
Land [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total property and equipment	75.7		75.7		65.6
Leasehold improvements and tooling [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total property and equipment	21.9		21.9		20.8
Evaluation units [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total property and equipment	20.2		20.2		20.1
Furniture and fixtures [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total property and equipment	16.7		16.7		14.7
Construction-in-progress [Member]
Property, Plant and Equipment, Net, by Type [Abstract]
Total property and equipment	$ 11.5		$ 11.5		$ 6.3

Investments in Privately-Held_2

Investments in Privately-Held Companies (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Investments, All Other Investments [Abstract]
Investments in equity securities of privately-held companies	$ 9.1
Investments in equity securities of privately-held companies		$ 12.1
Proceeds from sale of equity securities of privately held company	5.2
Recognized gain on sale of equity securities of privately held company	$ 2.2

Business Combination - Additio

Business Combination - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2018	Jun. 04, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill not deductible for tax purposes	$ 25.7		$ 14.6
Bradford [Member]
Business Acquisition [Line Items]
Subsequent decrease in intangible assets	0.8
Corresponding change to goodwill	0.6
Corresponding change to deferred tax asset	$ 0.2
Preliminary purchase price		$ 6.8
Goodwill not deductible for tax purposes		11.1
Identifiable intangible assets		8
Liabilities assumed		12.3
Cash consideration that may be paid as an earn-out subject to satisfaction of certain performance conditions		$ 2

Goodwill and Other Intangible_3

Goodwill and Other Intangible Assets - Net - Schedule of Changes in Carrying Value of Goodwill (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Goodwill [Roll Forward]
Balance - beginning of period	$ 14.6
Addition due to business combination	11.1
Balance - end of period	$ 25.7

Goodwill and Other Intangible_4

Goodwill and Other Intangible Assets - Net - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Indefinite-lived Intangible Assets [Line Items]
Goodwill	$ 25,700,000		$ 25,700,000		$ 14,600,000
Goodwill impairment	0		0
Amortization expense	$ 2,500,000	$ 2,000,000	$ 6,100,000	$ 6,500,000
In Process Research and Development [Member]
Indefinite-lived Intangible Assets [Line Items]
In-process research and development					$ 1,600,000
Developed Technology [Member]
Indefinite-lived Intangible Assets [Line Items]
Estimated useful life			4 years

Goodwill and Other Intangible_5

Goodwill and Other Intangible Assets - Net - Other Intangible Assets, Net (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Finite-Lived Intangible Assets, Net [Abstract]
Gross	$ 48.1		$ 48.1		$ 38.5
Accumulated Amortization	30		30		23.8
Total	18.1		18.1		14.7
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Gross					40.1
Net	18.1		18.1		$ 16.3
Amortization expense	2.5	$ 2	$ 6.1	$ 6.5
Developed Technologies and Other [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted average useful life			3 years 10 months 2 days		3 years 9 months 15 days
Finite-Lived Intangible Assets, Net [Abstract]
Gross	31.4		$ 31.4		$ 24
Accumulated Amortization	18.1		18.1		13.7
Total	13.3		$ 13.3		$ 10.3
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted average useful life			4 years 5 months 16 days		4 years 8 months 5 days
Finite-Lived Intangible Assets, Net [Abstract]
Gross	16.7		$ 16.7		$ 14.5
Accumulated Amortization	11.9		11.9		10.1
Total	$ 4.8		$ 4.8		4.4
In Process Research and Development [Member]
Indefinite-Lived Intangible Assets (Excluding Goodwill) [Abstract]
In-process research and development					$ 1.6

Goodwill and Other Intangible_6

Goodwill and Other Intangible Assets - Net - Estimated Future Amortization Expense (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Fiscal Years:
2,018	$ 2.5
2,019	8.2
2,020	4.6
2021 and thereafter	2.8
Total	$ 18.1	$ 14.7

Net Income Per Share , Calculat

Net Income Per Share , Calculation of Basic and Diluted (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Line Items]
Net income	$ 58.7	$ 26.7	$ 149.6	$ 60.4
Basic shares:
Weighted-average common shares outstanding-basic (in shares)	169.8	175.5	168.7	175.3
Diluted shares:
Weighted-average common shares outstanding-basic (in shares)	169.8	175.5	168.7	175.3
Effect of potentially dilutive securities:
Weighted-average shares used to compute diluted net income per share (in shares)	175.7	179	173.7	179
Basic (in dollars per share)	$ 0.35	$ 0.15	$ 0.89	$ 0.34
Diluted (in dollars per share)	$ 0.33	$ 0.15	$ 0.86	$ 0.34
Restricted Stock Units (RSUs) [Member]
Effect of potentially dilutive securities:
Employee stock options and purchase rights (in shares)	4.2	2.1	3.5	2.2
Stock Options [Member]
Effect of potentially dilutive securities:
Employee stock options and purchase rights (in shares)	1.6	1.3	1.4	1.4
ESPP [Member]
Effect of potentially dilutive securities:
Employee stock options and purchase rights (in shares)	0.1	0.1	0.1	0.1

Net Income Per Share , Anti Dil

Net Income Per Share , Anti Dilutive Securities (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	0.5	2.5	1.1	2.9
Restricted Stock Units (RSUs) [Member] | Stock Compensation Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	0.3	1	0.6	1.6
Stock Options [Member] | Stock Compensation Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	0	1.1	0.4	1.1
ESPP [Member] | Stock Compensation Plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Anti-dilutive securities (in shares)	0.2	0.4	0.1	0.2

Commitments and Contingencies M

Commitments and Contingencies Minimum Operating Lease Payments (Details) $ in Millions	Sep. 30, 2018USD ($)
Operating Lease Commitments:
Operating lease commitments, 2018	$ 4.1
Operating lease commitments, 2019	15.3
Operating lease commitments, 2020	11.6
Operating lease commitments, 2021	8
Operating lease commitments, 2022	5
Operating lease commitments, Thereafter	8
Operating lease commitments	52
Inventory purchase commitments:
Inventory purchase commitments, 2018	111.1
Inventory purchase commitments, 2019	58.7
Inventory purchase commitments, 2020	4.2
Inventory purchase commitments, 2021	0
Inventory purchase commitments, 2022	0
Inventory purchase commitments, Thereafter	0
Inventory purchase commitments	174
Other contractual commitments and open purchase orders:
Contractual Obligation, 2018	115.2
Contractual Obligation, 2019	74
Contractual Obligation, 2020	15.8
Contractual Obligation, 2021	8
Contractual Obligation, 2022	5
Contractual Obligation, Thereafter	8
Contractual Obligation	$ 226

Commitments and Contingencies_2

Commitments and Contingencies (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Rent expense	$ 4.4	$ 4.1	$ 13.1	$ 12.5
Inventory purchase commitments	174		174
Other contractual commitments and open purchase orders	$ 11.6		$ 11.6

Stockholders' Equity (Details)

Stockholders' Equity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract]
Expected term in years	4 years 4 months 24 days	4 years 4 months 24 days	4 years 4 months 24 days	4 years 4 months 24 days
Volatility	30.50%	33.10%	31.60%	36.10%
Risk-free interest rate	2.70%	1.80%	2.70%	1.90%
Dividend rate	0.00%	0.00%	0.00%	0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Balance - Beginning (in shares)			4.3
Granted (in shares)			0.8
Forfeited (in shares)			(0.1)
Exercised (in shares)			(1.8)
Balance - Ending (in shares)	3.2		3.2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Balance - Beginning (in dollars per share)			$ 27.50
Granted (in dollars per share)			51.29
Forfeited (in dollars per share)			31.90
Exercised (in dollars per share)			24.74
Balance - Ending (in dollars per share)	$ 34.69		$ 34.69
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options vested and expected to vest, Outstanding (in shares)	3.2		3.2
Options vested and expected to vest, Weighted average exercise price (in dollars per share)	$ 34.69		$ 34.69
Options vested and expected to vest, Weighted average remaining contractual life (in years)			4 years 1 month 17 days
Options vested and expected to vest, Aggregate intrinsic value	$ 183.4		$ 183.4
Options exercisable, Outstanding (in shares)	1.6		1.6
Options exercisable, Weighted average exercise price (in dollars per share)	$ 28.42		$ 28.42
Options exercisable, Weighted average remaining contractual life (in years)			2 years 9 months
Options exercisable, Aggregate intrinsic value	$ 104.9		$ 104.9
Compensation cost not yet recognized	$ 18.1		$ 18.1
Compensation cost not yet recognized period of recognition			2 years 8 months 12 days
Weighted-average fair value per share granted	$ 22.75	$ 11.09	$ 15.67	$ 12.17
Intrinsic value of options exercised	$ 14.1	$ 3.4	$ 53.6	$ 30.3
Total fair value of awards vested	$ 1.4	$ 1.6	$ 5.7	$ 6.7
Stock-based Compensation Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Remaining shares available for grant under the plans	54.5		54.5
Share Repurchase Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock repurchase program, remaining repurchase amount	$ 825.8		$ 825.8

Stockholders' Equity , Restrict

Stockholders' Equity , Restricted Stock Units Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Shares withheld for taxes	0.2	0.3	0.9	1
Tax withholding upon vesting of restricted stock awards	$ 15.5	$ 10	$ 48	$ 35.9
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Balance, beginning (shares)			8.5
Granted (shares)			3.7
Forfeited (shares)			(0.7)
Vested (shares)			(3.1)
Balance, ending (shares)	8.4		8.4
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Balance, weighted-average grant-date fair value per share (in dollars per share)—beginning			$ 34.79
Granted, weighted-average grant-date fair value per share (in dollars per share)			54.82
Forfeited, weighted-average grant-date fair value per share (in dollars per share)			38.24
Vested, weighted-average grant-date fair value per share (in dollars per share)			34.32
Balance, weighted-average grant-date fair value per share (in dollars per share)—ending	$ 44.48		$ 44.48
Compensation cost not yet recognized	$ 331.7		$ 331.7
Compensation cost not yet recognized period of recognition			2 years 9 months 15 days

Stockholders' Equity , ESPP Inf

Stockholders' Equity , ESPP Information (Details) - Employee Stock Purchase Plan [Member]	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term in years	6 months	6 months	6 months	6 months
Volatility	30.50%	26.20%	28.90%	29.50%
Risk-free interest rate	2.20%	1.20%	2.00%	0.90%
Dividend rate	0.00%	0.00%	0.00%	0.00%

Stockholders' Equity , Addition

Stockholders' Equity , Additional Information Related To ESPP (Details) - Employee Stock Purchase Plan [Member] - $ / shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average fair value per share granted (in dollars per share)	$ 18.28	$ 8.31	$ 14.14	$ 8.73
Shares issued under the ESPP (in shares)	0.4	0.5	1.1	1.1
Weighted-average price per share issued (in dollars per share)	$ 41.89	$ 31.49	$ 35.32	$ 29.52

Stockholders' Equity , Allocati

Stockholders' Equity , Allocation of Stock-Based Compensation Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 43.2	$ 34.3	$ 120.3	$ 102.7
Income tax benefit from employee stock option plans	6.8	6.7	19	21.1
Cost of product revenue [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	0.3	0.3	1.1	1
Cost of service revenue [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	2.8	2.4	8	7.2
Research and development [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	9.3	8	26.9	24.1
Sales and marketing [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	26	19.6	70.5	58.4
General and administrative [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	4.8	4	13.8	12
Restricted Stock Units (RSUs) [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	38.2	29.9	106.1	89.8
Stock Options [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	2.4	1.8	6.7	5.6
ESPP [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2.6	$ 2.6	$ 7.5	$ 7.3

Stockholders' Equity , Share Re

Stockholders' Equity , Share Repurchase Program (Details) - 2016 Share Repurchase Program [Member] - USD ($)	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended
	Jul. 31, 2018	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 31, 2016
Share Repurchase Program [Line Items]
Stock repurchase program, authorized amount	$ 1,500,000,000			$ 1,000,000,000		$ 200,000,000
Additional shares authorized	$ 500,000,000			$ 700,000,000	$ 100,000,000
Stock repurchased in the period, shares		0	2,540,547
Stock repurchased, average price (in dollars per share)			$ 46.08
Stock repurchased in the period, value			$ 117,100,000
Stock repurchase program, unused balance		$ 825,800,000	$ 825,800,000

Income Taxes , Narrative (Detai

Income Taxes , Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Mar. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Effective tax rate (percent)	17.00%	30.00%	6.00%	24.00%
U.S. federal and state taxes, withholding taxes and foreign taxes	$ 17,700,000	$ 12,700,000	$ 43,400,000	$ 30,000,000
Excess tax benefits on stock compensation	5,800,000	$ 1,800,000	16,200,000	$ 11,400,000
Unrecognized tax benefits and related interest release			18,000,000
Unrecognized tax benefits	64,100,000		64,100,000			$ 72,500,000
Unrecognized tax benefits that would favorably affect effective tax rate	62,800,000		62,800,000
Accrued interest and penalties related to uncertain tax benefits	12,200,000		12,200,000			$ 13,500,000
Possible decrease in unrecognized tax benefits	$ 8,000,000		$ 8,000,000
Approved refund claim					$ 6,800,000

Defined Contribution Plans (Det

Defined Contribution Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Retirement Benefits [Abstract]
Matching contribution on employee contributions, Percent			50.00%
Maximum contribution percentage of each employee's eligible earnings, Percent			4.00%
Matching contributions to the RRSP and 401(k) Plans	$ 1.4	$ 1.2	$ 4.4	$ 3.8

Segment Information (Details)

Segment Information (Details) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)reportable_segmentSegment_Managersbusiness_activityoperating_segment	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Segment Reporting Information [Line Items]
Business activity (in business activities) | business_activity			1
Segment managers responsible for operations (in segment managers) | Segment_Managers			0
Number of operating segments (in operating segments) | operating_segment			1
Number of reportable segments (in reportable segments) | reportable_segment			1
Revenue	$ 453.9	$ 374.2	$ 1,294.2	$ 1,078.3
Property and equipment - net	$ 265.4		$ 265.4		$ 245.4
Exclusive Networks Group [Member] | Customer Concentration Risk [Member] | Sales Revenue, Net [Member]
Segment Reporting Information [Line Items]
Concentration (percent)	29.00%	29.00%	29.00%	23.00%
Exclusive Networks Group [Member] | Customer Concentration Risk [Member] | Accounts Receivable [Member]
Segment Reporting Information [Line Items]
Concentration (percent)			33.00%		35.00%
Ingram Micro [Member] | Customer Concentration Risk [Member] | Sales Revenue, Net [Member]
Segment Reporting Information [Line Items]
Concentration (percent)	11.00%	11.00%	10.00%	10.00%
Ingram Micro [Member] | Customer Concentration Risk [Member] | Accounts Receivable [Member]
Segment Reporting Information [Line Items]
Concentration (percent)			10.00%
Americas [Member]
Segment Reporting Information [Line Items]
Revenue	$ 194	$ 161.2	$ 559.1	$ 468.3
Property and equipment - net	239.3		239.3		$ 219.7
U.S.
Segment Reporting Information [Line Items]
Revenue	146.8	123.7	425.3	367.1
Property and equipment - net	127.8		127.8		115.6
Other Americas
Segment Reporting Information [Line Items]
Revenue	31.2	24.4	86.4	64.6
Property and equipment - net	0.4		0.4		0.3
CANADA
Segment Reporting Information [Line Items]
Revenue	16	13.1	47.4	36.6
Property and equipment - net	111.1		111.1		103.8
EMEA
Segment Reporting Information [Line Items]
Revenue	165.4	138.3	474.3	394.2
Property and equipment - net	16.8		16.8		17.7
France
Segment Reporting Information [Line Items]
Property and equipment - net	13.3		13.3		11.9
Other EMEA
Segment Reporting Information [Line Items]
Property and equipment - net	3.5		3.5		5.8
APAC
Segment Reporting Information [Line Items]
Revenue	94.5	$ 74.7	260.8	$ 215.8
Property and equipment - net	9.3		9.3		8
All Countries [Domain]
Segment Reporting Information [Line Items]
Property and equipment - net	$ 265.4		$ 265.4		$ 245.4

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Loss (Changes in Accumulated Balances of Other Comprehensive Loss) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Accumulated Other Comprehensive (Loss) Income [Roll Forward]
Beginning balance	$ (0.8)
Other comprehensive loss before reclassifications	(0.2)
Amounts reclassified from accumulated other comprehensive loss	0
Net current-period other comprehensive loss	(0.2)
Ending balance	(1)
Tax Benefit Related To Items of Other Comprehensive Income or Loss [Roll Forward]
Beginning balance, tax	0.5
Other comprehensive income before reclassifications, tax	(0.1)
Amounts reclassified from accumulated other comprehensive income, tax	0
Net current-period other comprehensive income, tax	(0.1)
Ending balance, tax	0.4
Unrealized Gains and Losses on Investments [Member]
Accumulated Other Comprehensive (Loss) Income [Roll Forward]
Beginning balance	(1.3)
Other comprehensive loss before reclassifications	(0.1)
Amounts reclassified from accumulated other comprehensive loss	0
Net current-period other comprehensive loss	(0.1)
Ending balance	$ (1.4)

Subsequent Event (Details)

Subsequent Event (Details) $ in Millions	Oct. 23, 2018USD ($)
ZoneFox Limited [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Initial consideration, subject to certain adjustments	$ 18