F5 (FFIV) 10-K 16 Nov 21 2021 FY Annual report Financial data

Cover Page

Cover Page - USD ($)	12 Months Ended
	Sep. 30, 2021	Nov. 08, 2021	Mar. 31, 2021
Cover [Abstract]
Entity Central Index Key	0001048695
Document Type	10-K
Document Annual Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	000-26041
Entity Registrant Name	F5, Inc.
Entity Incorporation, State or Country Code	WA
Entity Tax Identification Number	91-1714307
Entity Address, Address Line One	801 5th Avenue
Entity Address, City or Town	Seattle
Entity Address, State or Province	WA
Entity Address, Postal Zip Code	98104
City Area Code	206
Local Phone Number	272-5555
Title of 12(b) Security	Common stock, no par value
Trading Symbol	FFIV
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 12,481,712,486
Entity Common Stock, Shares Outstanding		61,229,388
Documents Incorporated by Reference [Text Block]	Information required in response to Part III of this Form 10-K (Items 10, 11, 12, 13 and 14) is hereby incorporated by reference to the specified portions of the Registrant’s Definitive Proxy Statement for the Annual Shareholders Meeting for fiscal year 2021, which Definitive Proxy Statement shall be filed with the Securities and Exchange Commission pursuant to Regulation 14A within 120 days of the end of the fiscal year to which this Report relates
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--09-30
Amendment Flag	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
ASSETS
Cash and cash equivalents	$ 580,977	$ 849,556
Short-term investments	329,630	360,333
Accounts receivable, net of allowances of $3,696 and $3,105	340,536	296,183
Inventories	22,055	27,898
Other current assets	337,902	259,506
Total current assets	1,611,100	1,793,476
Property and equipment, net	191,164	229,239
Operating lease right-of-use assets	244,934	300,680
Long-term investments	132,778	102,939
Deferred tax assets	128,193	45,173
Goodwill	2,216,553	1,858,966
Other assets, net	472,558	347,447
Total assets	4,997,280	4,677,920
LIABILITIES AND SHAREHOLDERS’ EQUITY
Accounts payable	62,096	64,472
Accrued liabilities	341,487	321,398
Deferred revenue	968,669	883,134
Current portion of long-term debt	19,275	19,275
Total current liabilities	1,391,527	1,288,279
Deferred tax liabilities	2,414	602
Deferred revenue, long-term	521,173	389,498
Operating lease liabilities, long-term	296,945	338,715
Long-term debt	349,772	369,047
Other long-term liabilities	75,236	59,511
Total long-term liabilities	1,245,540	1,157,373
Commitments and contingencies (Note 13)
Shareholders’ equity
Preferred stock, no par value; 10,000 shares authorized, no shares outstanding	0	0
Common stock, no par value; 200,000 shares authorized, 60,652 and 61,099 shares issued and outstanding	192,458	305,453
Accumulated other comprehensive loss	(20,073)	(18,716)
Retained earnings	2,187,828	1,945,531
Total shareholders’ equity	2,360,213	2,232,268
Total liabilities and shareholders’ equity	$ 4,997,280	$ 4,677,920

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Statement of Financial Position [Abstract]
Accounts receivable, allowances	$ 3,696	$ 3,105
Preferred stock, par value (USD per share)	$ 0	$ 0
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value (USD per share)	$ 0	$ 0
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	60,652,000	61,099,000
Common stock, shares outstanding	60,652,000	61,099,000

Consolidated Income Statements

Consolidated Income Statements - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Net revenues
Net revenues	$ 2,603,416	$ 2,350,822	$ 2,242,447
Cost of net revenues
Cost of net revenues	493,146	407,887	356,577
Gross profit	2,110,270	1,942,935	1,885,870
Operating expenses
Sales and marketing	929,983	843,178	748,619
Research and development	512,627	441,324	408,058
General and administrative	273,635	258,366	210,730
Restructuring charges	0	7,800	0
Total	1,716,245	1,550,668	1,367,407
Income from operations	394,025	392,267	518,463
Other (expense) income, net	(7,088)	4,130	22,648
Income before income taxes	386,937	396,397	541,111
Provision for income taxes	55,696	88,956	113,377
Net income	$ 331,241	$ 307,441	$ 427,734
Net income per share - basic (USD per share)	$ 5.46	$ 5.05	$ 7.12
Weighted average shares - basic (shares)	60,707	60,911	60,044
Net income per share - diluted (USD per share)	$ 5.34	$ 5.01	$ 7.08
Weighted average shares - diluted (shares)	62,057	61,378	60,456
Product [Member]
Net revenues
Net revenues	$ 1,247,084	$ 1,025,856	$ 985,591
Cost of net revenues
Cost of net revenues	286,293	215,275	174,986
Service [Member]
Net revenues
Net revenues	1,356,332	1,324,966	1,256,856
Cost of net revenues
Cost of net revenues	$ 206,853	$ 192,612	$ 181,591

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income Statement - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income	$ 331,241	$ 307,441	$ 427,734
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Foreign currency translation adjustment	(68)	(572)	(837)
Available-for-sale securities:
Unrealized gains (losses) on securities, net of taxes of $(234), $76, and $954 for the years ended September 30, 2021, 2020, and 2019, respectively	(1,557)	809	3,715
Reclassification adjustment for realized losses included in net income, net of taxes of $(69), $(65), and $(35) for the years ended September 30, 2021, 2020, and 2019, respectively	268	237	110
Net change in unrealized (losses) gains on available-for-sale securities, net of tax	(1,289)	1,046	3,825
Total other comprehensive (loss) income	(1,357)	474	2,988
Comprehensive income	$ 329,884	$ 307,915	$ 430,722

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	$ (234)	$ 76	$ 954
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	$ (69)	$ (65)	$ (35)

Consolidated Statement Of Share

Consolidated Statement Of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Accumulated Other Comprehensive Loss	Retained Earnings
Balance, shares at Sep. 30, 2018		60,215,000
Balance at Sep. 30, 2018	$ 1,285,492	$ 20,427	$ (22,178)	$ 1,287,243
Exercise of employee stock options	159	$ 159
Exercise of employee stock options, shares		6,000
Issuance of stock under employee stock purchase plan	45,439	$ 45,439
Issuance of stock under employee stock purchase plan, shares		334,000
Issuance of restricted stock, shares		998,000
Repurchase of common stock	(201,045)	$ (88,110)		(112,935)
Repurchase of common stock, shares		(1,186,000)
Taxes paid related to net share settlement of equity awards	0
Stock-based compensation	164,682	$ 164,682
Net income	427,734			427,734
Other comprehensive income (loss)	2,988		2,988
Balance, shares at Sep. 30, 2019		60,367,000
Balance at Sep. 30, 2019	1,761,497	$ 142,597	(19,190)	1,638,090
Exercise of employee stock options	2,596	$ 2,596
Exercise of employee stock options, shares		104,000
Issuance of stock under employee stock purchase plan	50,239	$ 50,239
Issuance of stock under employee stock purchase plan, shares		419,000
Issuance of restricted stock, shares		1,027,000
Repurchase of common stock	(100,016)	$ (100,016)
Repurchase of common stock, shares		(799,000)
Taxes paid related to net share settlement of equity awards	(2,536)	$ (2,536)
Taxes paid related to net share settlement of equity awards, shares		(19,000)
Stock-based compensation	212,573	$ 212,573
Net income	307,441			307,441
Other comprehensive income (loss)	$ 474		474
Balance, shares at Sep. 30, 2020	61,099,000	61,099,000
Balance at Sep. 30, 2020	$ 2,232,268	$ 305,453	(18,716)	1,945,531
Exercise of employee stock options	$ 4,864	$ 4,864
Exercise of employee stock options, shares	163,880	164,000
Issuance of stock under employee stock purchase plan	$ 60,888	$ 60,888
Issuance of stock under employee stock purchase plan, shares		542,000
Issuance of restricted stock, shares		1,430,000
Repurchase of common stock	(500,000)	$ (411,056)		(88,944)
Repurchase of common stock, shares		(2,501,000)
Taxes paid related to net share settlement of equity awards	(14,032)	$ (14,032)
Taxes paid related to net share settlement of equity awards, shares		(82,000)
Stock-based compensation	246,341	$ 246,341
Net income	331,241			331,241
Other comprehensive income (loss)	$ (1,357)		(1,357)
Balance, shares at Sep. 30, 2021	60,652,000	60,652,000
Balance at Sep. 30, 2021	$ 2,360,213	$ 192,458	$ (20,073)	$ 2,187,828

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Operating activities
Net income	$ 331,241	$ 307,441	$ 427,734
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation	243,279	201,948	162,914
Depreciation and amortization	115,424	95,857	68,507
Non-cash operating lease costs	38,375	39,139	0
Deferred income taxes	(76,930)	7,293	7,440
Impairment of assets	40,698	9,673	6,273
Non-cash provisions for exit costs	0	0	8,211
Other	737	2,122	1,662
Changes in operating assets and liabilities (excluding effects of the acquisition of businesses):
Accounts receivable	(46,289)	46,502	(18,305)
Inventories	5,843	6,503	(3,832)
Other current assets	(84,328)	(49,895)	(75,449)
Other assets	(110,653)	(25,690)	(22,742)
Accounts payable and accrued liabilities	22,933	34,742	74,710
Deferred revenue	216,431	35,514	110,718
Lease liabilities	(51,565)	(50,251)	0
Net cash provided by operating activities	645,196	660,898	747,841
Investing activities
Purchases of investments	(472,165)	(584,240)	(602,987)
Maturities of investments	197,279	543,065	625,201
Sales of investments	271,521	309,687	278,244
Acquisition of businesses, net of cash acquired	(411,319)	(955,574)	(611,550)
Purchases of property and equipment	(30,651)	(59,940)	(103,542)
Net cash used in investing activities	(445,335)	(747,002)	(414,634)
Financing activities
Proceeds from the exercise of stock options and purchases of stock under employee stock purchase plan	65,752	52,835	45,598
Repurchase of common stock	(500,000)	(100,016)	(201,045)
Proceeds from term debt agreement	0	400,000	0
Payments on term debt agreement	(20,000)	(10,000)	0
Payments for debt issuance costs	0	(3,040)	0
Taxes paid related to net share settlement of equity awards	(14,032)	(2,536)	0
Net cash (used in) provided by financing activities	(468,280)	337,243	(155,447)
Net (decrease) increase in cash, cash equivalents and restricted cash	(268,419)	251,139	177,760
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(74)	(567)	(1,400)
Cash, cash equivalents and restricted cash, beginning of year	852,826	602,254	425,894
Cash, cash equivalents and restricted cash, end of year	584,333	852,826	602,254
Supplemental disclosures of cash flow information
Cash paid for taxes, net of refunds	99,378	80,236	100,569
Cash paid for amounts included in the measurement of operating lease liabilities	61,504	60,564	0
Cash paid for interest on long-term debt	5,280	6,568	0
Supplemental disclosures of non-cash activities
Right-of-use assets obtained in exchange for lease obligations	13,051	402,007	0
Capitalized leasehold improvements paid directly by landlord	$ 0	$ 0	$ 34,948

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	12 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary Of Significant Accounting Policies	Summary of Significant Accounting Policies The Company On November 12, 2021, the Company changed its corporate name from F5 Networks, Inc. to F5, Inc. (the "Company"). F5 is a leading provider of multi-cloud application security and delivery solutions which enable its customers to develop, deploy, operate, secure, and govern applications in any architecture, from on-premises to the public cloud. The Company's cloud, software, and hardware solutions enable its customers to deliver digital experiences to their customers faster, reliably, and at scale. The Company's enterprise-grade application services are available as cloud-based, software-as-a-service, and software-only solutions optimized for multi-cloud environments, with modules that can run independently, or as part of an integrated solution on its high-performance appliances. In connection with its solutions, the Company offers a broad range of professional services, including consulting, training, installation, maintenance, and other technical support services. On January 22, 2021, the Company completed the acquisition of Volterra, Inc. ("Volterra"), a provider of edge-as-a-service platform solutions. Accounting Principles The Company’s consolidated financial statements and accompanying notes are prepared on the accrual basis of accounting in accordance with generally accepted accounting principles in the United States of America (GAAP). Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. Use of Estimates and Assumptions The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Examples of estimates and assumptions include: revenue recognition, identifying and evaluating the performance obligations of contracts with non-standard terms, and the allocation of purchase consideration based on the relative fair value standalone sales price of these performance obligations; business combinations, including the determination of fair value for acquired developed technology assets and the evaluation and selection of significant assumptions such as revenue growth rate and technology migration curve; and the incremental borrowing rate for measuring lease obligations. Actual results may differ materially from management's estimates and assumptions due to risks and uncertainties, including uncertainty in the current economic environment due to the global impact of the COVID-19 pandemic. Cash, Cash Equivalents and Restricted Cash The Company considers all highly liquid investments with original maturities of three months or less to be cash equivalents. The Company invests its cash and cash equivalents in deposits with five major financial institutions, which, at times, exceed federally insured limits. The Company has not experienced any losses on its cash and cash equivalents. Amounts included in restricted cash represent those for which the Company's use is restricted by a contractual agreement. Investments The Company classifies its investment securities as available-for-sale. Investment securities, consisting of certificates of deposit, corporate and municipal bonds and notes, the United States government and agency securities and international government securities are reported at fair value with the related unrealized gains and losses included as a component of accumulated other comprehensive income (loss) in shareholders’ equity. Realized gains and losses and impairments due to credit losses, in which the fair value of a security is below its amortized cost and management’s intent is to sell the impaired security prior to its recovery, are included in other income (expense). An allowance for credit losses for the excess of amortized cost over the expected cash flows is recorded in other income, net in the Company's consolidated income statements. The cost of investments for purposes of computing realized and unrealized gains and losses is based on the specific identification method. Investments in securities with maturities of less than one year or where management’s intent is to use the investments to fund current operations are classified as short-term investments. Investments with maturities of greater than one year are classified as long-term investments. Accounts Receivable Trade accounts receivable are recorded at the invoiced amount, net of allowances for credit losses for any potential uncollectible amounts. The allowance for credit losses is based on the assessment of the collectability of accounts. Management regularly reviews the adequacy of the allowance for credit losses on a collective basis by considering the age of each outstanding invoice, each customer’s expected ability to pay and collection history, current market conditions, and reasonable and supportable forecasts of future economic conditions to determine whether the allowance is appropriate. Accounts receivable deemed uncollectible are charged against the allowance for credit losses when identified. For fiscal years ended September 30, 2021 and 2020, the allowance for credit losses activity was not material. Concentration of Credit Risk The Company extends credit to customers and is therefore subject to credit risk. The Company performs initial and ongoing credit evaluations of its customers’ financial condition and does not require collateral. An allowance for credit losses is recorded for any potential uncollectible amount. Estimates are used in determining the allowance for credit losses in accordance with the Accounts Receivable policy. See Note 16 - Segment Information, for disaggregated accounts receivable by significant customer. The Company maintains its cash and investment balances with high credit quality financial institutions. Fair Value of Financial Instruments Short-term and long-term investments are recorded at fair value as the underlying securities are classified as available-for-sale with any unrealized gain or loss being recorded to other comprehensive income. The fair value for securities held is determined using quoted market prices, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency. Inventories The Company outsources the manufacturing of its pre-configured hardware platforms to contract manufacturers, who assemble each product to the Company’s specifications. As protection against component shortages and to provide replacement parts for its service teams, the Company also stocks limited supplies of certain key product components. The Company reduces inventory to net realizable value based on excess and obsolete inventories determined primarily by historical usage and forecasted demand. Inventories consist of hardware and related component parts and are recorded at the lower of cost and net realizable value (as determined by the first-in, first-out method). Property and Equipment Property and equipment are stated at net book value. Depreciation of property and equipment are provided using the straight-line method over the estimated useful lives of the assets, ranging from two Business Combinations The Company’s business combinations are accounted for under the acquisition method. Management allocates the fair value of purchase consideration to the tangible and intangible assets acquired and liabilities assumed based on their estimated fair values. The excess of the fair value of purchase consideration over the fair values of these identifiable assets and liabilities is recorded as goodwill. Such valuations require management to make significant estimates and assumptions, especially with respect to intangible assets. On January 22, 2021, the Company completed its acquisition of Volterra, Inc. for a total purchase price of $427.2 million, of which approximately $59.5 million of finite-lived developed technology was recorded. Management valued the developed technology using the relief-from-royalty method under the income approach. Management applied significant judgment in estimating the fair value of the acquired developed technology, which involved the use of a significant assumption with respect to the royalty rate. Goodwill Goodwill represents the excess purchase price over the estimated fair value of net assets acquired as of the acquisition date. The Company tests goodwill for impairment on an annual basis and between annual tests when impairment indicators are identified, and goodwill is written down when impaired. For its annual goodwill impairment test in all periods to date, the Company has operated under one reporting unit and the fair value of its reporting unit has been determined by the Company’s enterprise value. The Company performs its annual goodwill impairment test during the second fiscal quarter. For its annual impairment test performed in the second quarter of fiscal 2021, the Company completed a quantitative assessment and determined that there was no impairment of goodwill. The Company also considered potential impairment indicators of goodwill at September 30, 2021 and noted no indicators of impairment. Intangible Assets Intangible assets with finite lives consist of acquired developed technology, customer relationships, patents and trademarks, trade names, and non-compete covenants acquired through business combination or asset acquisition. Intangible assets acquired through business combination are recorded at their respective estimated fair values upon acquisition close. Other intangible assets acquired through asset acquisition are recorded at their respective cost. The Company determines the estimated useful lives for acquired intangible assets based on the expected future cash flows associated with the respective asset. The Company's intangible assets with finite lives are amortized using the straight-line method over their estimated useful lives, ranging from two Software Development Costs The authoritative guidance requires certain internal software development costs related to software to be sold to be capitalized upon the establishment of technological feasibility. Capitalized software development costs are amortized over the remaining estimated economic life of the product. The Company's software development costs incurred subsequent to achieving technological feasibility have not been significant and, as a result, all software development costs have been expensed as research and development activities as incurred. Internal-Use Software The Company capitalizes costs incurred during the application development stage associated with the development of internal-use software systems. The capitalized costs are then amortized over the estimated useful life of the software, which is generally three Impairment of Long-Lived Assets The Company assesses the impairment of long-lived assets whenever events or changes in business circumstances indicate that the carrying amount of an asset may not be recoverable. When such events occur, management determines whether there has been impairment by comparing the anticipated undiscounted net future cash flows to the related asset’s carrying value. If impairment exists, the asset is written down to its estimated fair value. Revenue Recognition On October 1, 2018, the Company adopted the new revenue recognition standard by applying the modified retrospective approach to those contracts which were not completed as of October 1, 2018. Results for reporting periods beginning after October 1, 2018 are presented under the new revenue recognition standard, while prior period amounts are not adjusted and continue to be reported under the accounting standards in effect for the prior periods. The Company sells products through distributors, resellers, and directly to end users. Revenue related to the Company's contracts with customers is recognized by following a five-step process: • Identify the contract(s) with a customer. Evidence of a contract generally consists of a purchase order issued pursuant to the terms and conditions of a distributor, reseller or end user agreement. • Identify the performance obligations in the contract. Performance obligations are identified in the Company's contracts and include hardware, hardware-based software, software-only solutions, cloud-based subscription services as well as a broad range of service performance obligations including consulting, training, installation and maintenance. • Determine the transaction price. The purchase price stated in an agreed upon purchase order is generally representative of the transaction price. The Company offers several programs in which customers are eligible for certain levels of rebates if certain conditions are met. When determining the transaction price, the Company considers the effects of any variable consideration. • Allocate the transaction price to the performance obligations in the contract. The transaction price in a contract is allocated based upon the relative standalone selling price of each distinct performance obligation identified in the contract. • Recognize revenue when (or as) the entity satisfies a performance obligation. The Company satisfies performance obligations either over time or at a point in time as discussed in further detail below. Revenue is recognized at the time the related performance obligation is satisfied by transferring control of promised products and services to a customer. Revenue is recognized net of any taxes collected, which are subsequently remitted to governmental authorities. Shipping and handling fees charged to the Company’s 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. The following is a description of the principal activities from which the Company generates revenue: Product Revenue from the sale of the Company's hardware and perpetual software products is generally recognized at a point in time when the product has been fulfilled and the customer is obligated to pay for the product. The Company also offers several products by subscription, either through term-based license agreements or as a service through its cloud-based platform. Revenue for term-based license agreements is recognized at a point in time, when the Company delivers the software license to the customer and the subscription term has commenced. For the Company's software-as-a-service offerings, revenue is recognized ratably as the services are provided. Hardware, including the software run on those devices is considered Systems revenue. Perpetual or subscription software offerings that are deployed on a standalone basis, along with software sold as a service are considered Software revenue. When rights of return are present and the Company cannot estimate returns, revenue is recognized when such rights of return lapse. Payment terms to customers are generally net 30 days to net 60 days. Global Services Revenues for post-contract customer support (PCS) are recognized on a straight-line basis over the service contract term. PCS includes a limited period of telephone support, updates, repair or replacement of any failed product or component that fails during the term of the agreement, bug fixes and rights to upgrades, when and if available. Consulting services are customarily billed at fixed hourly rates, plus out-of-pocket expenses, and revenues are recognized as the consulting is completed. Similarly, training revenue is recognized as the training is completed. Contract Acquisition Costs Sales commissions earned by the Company's sales force are considered incremental and recoverable costs of obtaining a contract with a customer. Sales commissions for initial service contracts and subscription offerings are deferred and then amortized as an expense on a straight-line basis over the period of benefit which management has determined to be 4.5 years and 3 years, respectively. Significant Judgments The Company enters into certain contracts with customers, including flexible consumption programs and multi-year subscriptions, with non-standard terms and conditions. Management exercises significant judgment in assessing contractual terms in these arrangements to identify and evaluate performance obligations. Management allocates consideration to each performance obligation based on relative fair value using standalone selling price and recognizes associated revenue as control is transferred to the customer. Guarantees and Product Warranties In the normal course of business to facilitate sales of its products, the Company indemnifies other parties, including customers, resellers, lessors, and parties to other transactions with the Company, with respect to certain matters. The Company has agreed to hold the other party harmless against losses arising from a breach of representations or covenants, or out of intellectual property infringement or other claims made against certain parties. These agreements may limit the time within which an indemnification claim can be made and the amount of the claim. The Company has entered into indemnification agreements with its officers and directors, and the Company’s bylaws contain similar indemnification obligations to the Company’s agents. It is not possible to determine the maximum potential amount under these indemnification agreements due to the limited history of prior indemnification claims and the unique facts and circumstances involved in each particular agreement. The Company offers warranties of one year for hardware for those customers without service contracts, with the option of purchasing additional warranty coverage in yearly increments. The Company accrues for warranty costs as part of its cost of sales based on associated material product costs and technical support labor costs. Warranty expense and accrued warranty costs were not material for all periods presented. Research and Development Research and development expenses consist of salaries and related benefits of product development personnel, prototype materials and expenses related to the development of new and improved products, and an allocation of facilities, depreciation and amortization expense. Research and development expenses are reflected in the income statements as incurred. Advertising Advertising costs are expensed as incurred. The Company incurred $10.0 million, $7.8 million and $4.7 million in advertising costs during the fiscal years 2021, 2020 and 2019, respectively. Income Taxes Deferred income tax assets and liabilities are determined based upon differences between the financial statement and income tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The realization of deferred tax assets is based on historical tax positions and estimates of future taxable income. A valuation allowance is recorded when it is more-likely-than-not that some of the deferred tax assets will not be realized. The Company assesses whether tax benefits claimed or expected to be claimed on a tax return should be recorded in the financial statements. The Company may recognize the tax benefit from an uncertain tax position only if it is more-likely-than-not that the tax position will be sustained on examination by the taxing authorities, including resolution of any related appeals or litigation processes, based on the technical merits of the position. The tax benefits to be recognized in the financial statements from such a position is measured as the largest amount of benefit that has a greater than fifty percent likelihood of being realized upon ultimate settlement. The Company adjusts these liabilities based on a variety of factors, including the evaluation of information not previously available. These adjustments are reflected as increases or decreases to income tax expense in the period in which new information is available. The Company has made an accounting policy election to treat taxes under the global intangible low-taxed income (GILTI) provision as a current period expense. Foreign Currency The functional currency for the Company’s foreign subsidiaries is either the U.S. dollar or the local currency depending on the assessment of management. An entity’s functional currency is determined by the currency of the economic environment in which the majority of cash is generated and expended by the entity. The financial statements of all majority-owned subsidiaries and related entities, with a functional currency other than the U.S. dollar, have been translated into U.S. dollars. All assets and liabilities of the respective entities are translated at year-end exchange rates and all revenues and expenses are translated at average rates during the respective period. Translation adjustments are reported as other comprehensive income (loss) in the consolidated statements of comprehensive income. Foreign currency transaction gains and losses are a result of the effect of exchange rate changes on transactions denominated in currencies other than the functional currency, including U.S. dollars. Gains and losses on those foreign currency transactions are included in determining net income or loss for the period of exchange and are recorded in other income, net. The net effect of foreign currency gains and losses was not material during the fiscal years ended September 30, 2021, 2020 and 2019. Segments Management has determined that the Company is organized as, and operates in, one reportable segment and operating segment: the development, marketing and sale of application services that optimize the security, performance and availability of network applications, servers and storage systems. Stock-based Compensation The Company issues incentive awards to its employees through stock-based compensation consisting of restricted stock units (RSUs). RSUs are payable in shares of the Company’s common stock as the periodic vesting requirements are satisfied, generally over one The Company offers an Employee Stock Purchase Plan (ESPP) that permits eligible employees to purchase shares of the Company’s common stock at a discount. In determining the fair value of shares issued under the ESPP, the Company uses the Black-Scholes option pricing model. The assumptions within the option pricing model are based on management’s best estimates at that time, which impact the fair value of the ESPP option calculated under the Black-Scholes methodology and, ultimately, the expense that will be recognized over the life of the ESPP option. The Company has also issued stock options as replacement awards, most notably for those assumed as part of business combinations. The Company used the Black-Scholes option pricing model to determine the fair value of the stock option replacement awards. The assumptions within the option pricing model are based on management’s best estimates at that time, which impact the fair value of the option calculated under the Black-Scholes methodology and, ultimately, the expense that will be recognized over the term of the option. The Company accounts for stock-based compensation using the straight-line attribution method for recognizing compensation expense. The Company recognizes compensation expense for only the portion of stock-based awards that are expected to vest. Therefore, the Company applies estimated forfeiture rates that are derived from historical employee termination behavior. Based on historical differences with forfeitures of stock-based awards granted to the Company’s executive officers and Board of Directors versus grants awarded to all other employees, the Company has developed separate forfeiture expectations for these two groups. The Company issues incentive awards to certain current executive officers as part of its annual equity awards program. A portion of the aggregate number of RSUs issued to executive officers vest in equal quarterly increments, and a portion is subject to the Company achieving specified performance goals. For the performance stock awards granted prior to fiscal 2018, attainment is based on the Company achieving specific quarterly revenue and EBITDA targets. In each case, 70% of the quarterly performance stock grant is based on achieving at least 80% of the quarterly revenue goal set by the Company's Board of Directors, and the other 30% is based on achieving at least 80% of the quarterly EBITDA goal set by the Company's Board of Directors. The quarterly performance stock grant is paid linearly over 80% of the targeted goals. At least 100% of both goals must be attained in order for the quarterly performance stock grant to be awarded over 100%. Each goal is evaluated individually and subject to the 80% achievement threshold and the 100% over-achievement threshold. Each goal is also capped at achievement of 200% above target. In fiscal 2018, the Company's Talent and Compensation Committee adopted a new set of metrics for the performance stock awards that are differentiated from the quarterly revenue and EBITDA measures, including (1) 50% of the annual performance stock grant is based on achieving 80% of the annual revenue goal set by the Company’s Board of Directors; (2) 25% of the annual performance stock grant is based on achieving at least an 18% increase in annual software revenue compared to the prior year; and (3) 25% of the annual performance stock grant is based on relative total shareholder return (TSR) benchmarked to the S&P 500 index. In each case, no vesting or payment with respect to a performance goal shall occur unless a minimum threshold is met for the applicable goal. Vesting and payment with respect to the performance goal is linear above the threshold of the applicable goal and is capped at achievement of 200% above target. The Company recognizes compensation costs for awards with performance conditions and market conditions on a straight-line basis over the requisite service period for each separately vesting portion of the award and, for awards with performance conditions, when it concludes it is probable that the performance condition will be achieved. The Company reassesses the probability of vesting at each balance sheet date and adjusts compensation costs based on the probability assessment. Comprehensive Income Comprehensive income includes certain changes in equity that are excluded from net income. Specifically, unrealized gains or losses on securities and foreign currency translation adjustments. These changes are included in accumulated other comprehensive income or loss. Recently Adopted Accounting Standards In August 2018, the FASB issued ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40) (ASU 2018-15), which aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software, and hosting arrangements that include an internal-use software license. The accounting for the service element of a hosting arrangement that is a service contract is not affected by the amendments in this update. The Company adopted this new standard prospectively on October 1, 2020. The adoption of this standard did not have a material impact to the Company’s consolidated financial statements or disclosures. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (ASU 2016-13), which modifies the accounting for credit losses for most financial assets and requires the use of an expected loss model, replacing the currently used incurred loss method. Under this model, entities will be required to estimate the lifetime expected credit loss on such instruments and record an allowance to offset the amortized cost basis of the financial asset, resulting in a net presentation of the amount expected to be collected on the financial asset. The Company adopted this new standard on October 1, 2020 using the modified retrospective approach. The adoption of this standard did not have a material impact on the Company’s condensed consolidated financial statements. Recently Issued Accounting Pronouncements

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Sep. 30, 2021
Revenue from Contracts with Customers [Abstract]
Revenue from Contract with Customers	Revenue from Contracts with Customers Capitalized Contract Acquisition Costs The table below shows significant movements in capitalized contract acquisition costs (current and noncurrent) for the years ended September 30, 2021, 2020, and 2019 (in thousands): 2021 2020 2019 Balance, beginning of year $ 70,396 $ 59,446 $ — Impacts from adoption of ASC 606 — — 54,608 Additional capitalized contract acquisition costs 41,719 43,557 33,925 Amortization of capitalized contract acquisition costs (34,279) (32,607) (29,087) Balance, end of year $ 77,836 $ 70,396 $ 59,446 Amortization of capitalized contract acquisition costs was $34.3 million, $32.6 million, and $29.1 million for the years ended September 30, 2021, 2020, and 2019, respectively, and is recorded in Sales and Marketing expense in the accompanying consolidated income statements. There was no impairment of any capitalized contract acquisition costs during any period presented. Contract Balances Timing may differ between the satisfaction of performance obligations and the invoicing and collection of amounts related to the Company's contracts with customers. A receivable is recorded when the Company has an unconditional right to payment for a non-cancellable contract. Unbilled receivables represent amounts related to performance obligations that are satisfied but not yet billed, in addition to contracts that have started, but have not been fully billed. Liabilities are recorded for amounts that are collected in advance of the satisfaction of performance obligations. These liabilities are classified as current and non-current deferred revenue. The table below shows significant movements in unbilled receivables (current and noncurrent) for the years ended September 30, 2021, 2020, and 2019 (in thousands): 2021 2020 2019 Balance, beginning of year $ 200,472 $ 132,492 $ — Impacts from adoption of ASC 606 — — 57,499 Revenue recognized during period but not yet billed 60,511 37,260 27,459 Unbilled receivables additions 256,437 129,578 88,068 Unbilled receivables reclassified to accounts receivable (143,138) (98,858) (40,534) Balance, end of year $ 374,282 $ 200,472 $ 132,492 As of September 30, 2021, unbilled receivables that are expected to be reclassified to accounts receivable within the next 12 months are included in other current assets, with those expected to be transferred to receivables in more than 12 months included in other assets. The table below shows significant movements in the deferred revenue balances (current and noncurrent) for the year ended September 30, 2021, 2020, and 2019 (in thousands): 2021 2020 2019 Balance, beginning of year $ 1,272,632 $ 1,198,116 $ 1,015,321 Impacts from adoption of ASC 606 — — 68,078 Amounts added but not recognized as revenues 1,122,081 850,022 866,142 Deferred revenue acquired through acquisition of businesses 779 39,000 — Revenues recognized related to the opening balance of deferred revenue (905,650) (814,506) (751,425) Balance, end of year $ 1,489,842 $ 1,272,632 $ 1,198,116 Remaining Performance Obligations Remaining performance obligations represent the amount of the transaction price under contracts with customers that are attributable to performance obligations that are unsatisfied or partially satisfied at the reporting date. As of September 30, 2021, the total non-cancelable remaining performance obligations under the Company's contracts with customers was approximately $1.5 billion and the Company expects to recognize revenues on approximately 65.0% of these remaining performance obligations over the next 12 months, 21.3% in year two, and the remaining balance thereafter. See Note 16 - Segment Information, for disaggregated revenue by significant customer and geographic region, as well as disaggregated product revenue by systems and software.

Business Combinations

Business Combinations	12 Months Ended
	Sep. 30, 2021
Business Combinations [Abstract]
Business Combinations	Business Combinations Fiscal Year 2021 Acquisition of Volterra, Inc. On January 5, 2021, the Company entered into a Merger Agreement (the “Volterra Merger Agreement”) with Volterra, Inc. ("Volterra"), a provider of edge-as-a-service platform solutions. The transaction closed on January 22, 2021 with Volterra becoming a wholly-owned subsidiary of F5. With the addition of Volterra’s technology platform, F5 is creating an edge platform built for enterprises and service providers that will be security-first and app-driven with unlimited scale. Pursuant to the Volterra Merger Agreement, at the effective time of the Merger, the capital stock of Volterra and the vested outstanding and unexercised stock options in Volterra were cancelled and converted to the right to receive approximately $427.2 million in cash, subject to certain adjustments and conditions set forth in the Volterra Merger Agreement. The unvested stock options and restricted stock units in Volterra held by continuing employees of Volterra were assumed by F5, on the terms and conditions set forth in the Volterra Merger Agreement. The Company incurred $9.5 million of transaction costs associated with the acquisition which was included in General and Administrative expenses in fiscal 2021. As a result of the acquisition, the Company acquired all the assets and assumed all the liabilities of Volterra. The goodwill related to the Volterra acquisition is comprised primarily of expected synergies from combining operations and the acquired intangible assets that do not qualify for separate recognition. Goodwill related to the Volterra acquisition is not expected to be deductible for tax purposes. The results of operations of Volterra have been included in the Company's consolidated financial statements from the date of acquisition. The allocated purchase consideration to assets acquired and liabilities assumed based on preliminary estimated fair values is presented in the following table (in thousands): Estimated Useful Life Assets acquired Cash, cash equivalents, and restricted cash $ 14,012 Other tangible assets acquired, at fair value 7,499 Identifiable intangible assets: Developed technology 59,500 7 years Customer relationships 500 1 year Goodwill 351,417 Total assets acquired 432,928 Liabilities assumed (5,686) Net assets acquired $ 427,242 The initial allocation of the purchase price was based on preliminary valuations and assumptions and is subject to change within the measurement period. The Company expects to finalize the allocation of the purchase price as soon as practicable and no later than one year from the acquisition date. The developed technology intangible asset will be amortized on a straight-line basis over its estimated useful life of seven years and included in cost of net product revenues. The customer relationships intangible asset will be amortized on a straight-line basis over its estimated useful life of one year and included in sales and marketing expenses. The weighted-average life of the amortizable intangible assets recognized from the Volterra acquisition was 6.95 years as of January 22, 2021, the date the transaction closed. The estimated useful lives for the acquired intangible assets were based on the expected future cash flows associated with the respective asset. Since the Volterra acquisition was completed on January 22, 2021, the F5 and Volterra teams have been executing a plan to integrate ongoing operations. The pro forma financial information, as well as the revenue and earnings generated by Volterra, were not material to the Company's operations for the periods presented. Fiscal Year 2020 Acquisition of Shape Security, Inc. On December 19, 2019, the Company entered into a Merger Agreement (the "Shape Merger Agreement") with Shape Security, Inc. ("Shape"), a provider of fraud and abuse prevention solutions. The transaction closed on January 24, 2020 with Shape becoming a wholly-owned subsidiary of F5. This acquisition brings together F5’s expertise in protecting applications across multi-cloud environments with Shape’s fraud and abuse prevention capabilities. Pursuant to the Shape Merger Agreement, at the effective time of the acquisition, the capital stock of Shape and the vested outstanding and unexercised stock options in Shape were cancelled and converted to the right to receive approximately $1.0 billion in cash, subject to certain adjustments and conditions set forth in the Shape Merger Agreement, and the unvested stock options and restricted stock units in Shape held by continuing employees of Shape were assumed by F5, on the terms and conditions set forth in the Shape Merger Agreement. Included in cash consideration was $23.2 million of transaction costs paid by F5 on behalf of Shape. In addition, the Company incurred $15.3 million of transaction costs associated with the acquisition which was included in General and Administrative expenses in fiscal 2020. As a result of the acquisition, the Company acquired all the assets and assumed all the liabilities of Shape. The goodwill related to the Shape acquisition is comprised primarily of expected synergies from combining operations and the acquired intangible assets that do not qualify for separate recognition. Goodwill related to the Shape acquisition is not expected to be deductible for tax purposes. The results of operations of Shape have been included in the Company's consolidated financial statements from the date of acquisition. The allocated purchase consideration to assets acquired and liabilities assumed is presented in the following table (in thousands): Estimated Useful Life Assets acquired Cash, cash equivalents, and restricted cash $ 53,934 Fair value of tangible assets: Accounts receivable 21,077 Deferred tax assets 29,848 Operating lease right-of-use assets 29,644 Other tangible assets 22,571 Identifiable intangible assets: Developed technology 120,000 7 years Customer relationships 21,000 4 years Trade name 9,500 5 years Goodwill 798,867 Total assets acquired $ 1,106,441 Liabilities assumed Deferred revenue $ (39,000) Operating lease liabilities (30,773) Other assumed liabilities (18,571) Total liabilities assumed $ (88,344) Net assets acquired $ 1,018,097 The measurement period for the Shape acquisition lapsed in the second quarter of fiscal 2021. In the first and second fiscal quarters of 2021, the Company recorded a net decrease to the carrying amount of goodwill of $0.7 million to reflect the final adjustments to consideration exchanged for the purchase of Shape within the post-close measurement period. The developed technology intangible asset will be amortized on a straight-line basis over its estimated useful life of seven years and included in cost of net product revenues. The trade names and customer relationships intangible assets will be amortized on a straight-line basis over their estimated useful lives of five years and four years, respectively, and included in sales and marketing expenses. The weighted average life of the amortizable intangible assets recognized from the Shape acquisition was 6.5 years as of January 24, 2020, the date the transaction closed. The estimated useful lives for the acquired intangible assets were based on the expected future cash flows associated with the respective asset. Since the Shape acquisition was completed on January 24, 2020, the F5 and Shape teams have been executing a plan to integrate ongoing operations. The pro forma financial information, as well as the revenue and earnings generated by Shape, were not material to the Company's operations for the periods presented. Fiscal Year 2019 Acquisition of Nginx, Inc. On March 9, 2019, the Company entered into a Merger Agreement (the "NGINX Merger Agreement") with Nginx, Inc. ("NGINX"), a provider of open source web server software and application delivery solutions. The transaction closed on May 8, 2019 with NGINX becoming a wholly-owned subsidiary of F5. Pursuant to the NGINX Merger Agreement, at the effective time of the Merger, the capital stock of NGINX and the vested outstanding and unexercised stock options in NGINX were cancelled and converted to the right to receive approximately $643.2 million in cash, subject to certain adjustments and conditions set forth in the NGINX Merger Agreement, and the unvested stock options and restricted stock units in NGINX held by continuing employees of NGINX were assumed by F5, on the terms and conditions set forth in the NGINX Merger Agreement. Included in cash consideration was $19.0 million of transaction costs paid by F5 on behalf of NGINX. In addition, the Company incurred $1.0 million of transaction costs associated with the acquisition which was included in General and Administrative expenses for fiscal 2019. As a result of the acquisition, the Company acquired all the assets and assumed all the liabilities of NGINX. The goodwill related to the NGINX acquisition is comprised primarily of expected synergies from combining operations and the acquired intangible assets that do not qualify for separate recognition. The results of operations of NGINX have been included in the Company's consolidated financial statements from the date of acquisition. The allocated purchase consideration to assets acquired and liabilities assumed is presented in the following table (in thousands): Estimated Useful Life Assets acquired Cash and cash equivalents $ 29,911 Fair value of tangible assets: Other tangible assets 23,699 Identifiable intangible assets: Developed technology 62,500 7 years Customer relationships 12,000 15 years Trade name 14,500 7 years Non-competition agreements 300 2 years Goodwill 510,328 Total assets acquired $ 653,238 Liabilities assumed Other assumed liabilities $ (9,116) Total liabilities assumed $ (9,116) Net assets acquired $ 644,122 The measurement period for the NGINX acquisition lapsed during the third quarter of fiscal 2020. The developed technology intangible asset will be amortized on a straight-line basis over its estimated useful life of seven years and included in cost of net product revenues. The trade names and customer relationships intangible assets will be amortized on a straight-line basis over their estimated useful lives of seven years and fifteen years, respectively, and included in sales and marketing expenses. The weighted average life of the amortizable intangible assets recognized from the NGINX acquisition was 8.1 years as of May 8, 2019, the date the transaction closed. The estimated useful lives for the acquired intangible assets were based on the expected future cash flows associated with the respective asset. The allocated purchase consideration to assets acquired and liabilities assumed resulted in tax deductible goodwill of $500.5 million. The pro forma financial information, as well as the revenue and earnings generated by NGINX, were not material to the Company's operations for the periods presented.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements In accordance with the authoritative guidance on fair value measurements and disclosure under GAAP, the Company determines fair value using a fair value hierarchy that distinguishes between market participant assumptions developed based on market data obtained from sources independent of the reporting entity, and the reporting entity’s own assumptions about market participant assumptions developed based on the best information available in the circumstances and expands disclosure about fair value measurements. Fair value is the price that would be received to sell an asset or paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants at the measurement date, essentially the exit price. The levels of fair value hierarchy are: Level 1: Quoted prices in active markets for identical assets and liabilities at the measurement date that the Company has the ability to access. Level 2: Observable inputs other than quoted prices included in Level 1, such as quoted prices for similar assets and liabilities in active markets; quoted prices for identical or similar assets and liabilities in markets that are not active; or other inputs that are observable or can be corroborated by observable market data. Level 3: Unobservable inputs for which there is little or no market data available. These inputs reflect management’s assumptions of what market participants would use in pricing the asset or liability. Level 1 investments are valued based on quoted market prices in active markets and include the Company’s cash equivalent investments. Level 2 investments, which include investments that are valued based on quoted prices in markets that are not active, broker or dealer quotations, actual trade data, benchmark yields or alternative pricing sources with reasonable levels of price transparency, include the Company’s certificates of deposit, corporate bonds and notes, municipal bonds and notes, U.S. government securities, U.S. government agency securities and international government securities. Fair values for the Company’s level 2 investments are based on similar assets without applying significant judgments. In addition, all of the Company’s level 2 investments have a sufficient level of trading volume to demonstrate that the fair values used are appropriate for these investments. A financial instrument’s level within the fair value hierarchy is based upon the lowest level of any input that is significant to the fair value measurement. However, the determination of what constitutes “observable” requires significant judgment by the Company. The Company considers observable data to be market data which is readily available, regularly distributed or updated, reliable and verifiable, not proprietary, and provided by independent sources that are actively involved in the relevant market. Assets and Liabilities Measured and Recorded at Fair Value on a Recurring Basis The Company’s financial assets measured at fair value on a recurring basis subject to the disclosure requirements at September 30, 2021, were as follows (in thousands): Fair Value Measurements at Reporting Date Using Fair Value at Quoted Prices in Significant Significant Cash equivalents $ 17,150 $ 4,397 $ — $ 21,547 Short-term investments Available-for-sale securities — certificates of deposit — 255 — 255 Available-for-sale securities — corporate bonds and notes — 186,107 — 186,107 Available-for-sale securities — municipal bonds and notes — 13,566 — 13,566 Available-for-sale securities — U.S. government securities — 102,615 — 102,615 Available-for-sale securities — U.S. government agency securities — 27,087 — 27,087 Long-term investments Available-for-sale securities — corporate bonds and notes — 53,107 — 53,107 Available-for-sale securities — municipal bonds and notes — 11,111 — 11,111 Available-for-sale securities — U.S. government securities — 59,608 — 59,608 Available-for-sale securities — U.S. government agency securities — 8,952 — 8,952 Total $ 17,150 $ 466,805 $ — $ 483,955 The Company’s financial assets measured at fair value on a recurring basis subject to the disclosure requirements at September 30, 2020, were as follows (in thousands): Fair Value Measurements at Reporting Date Using Fair Value at Quoted Prices in Significant Significant Cash equivalents $ 43,553 $ 207,417 $ — $ 250,970 Short-term investments Available-for-sale securities — corporate bonds and notes — 189,662 — 189,662 Available-for-sale securities — municipal bonds and notes — 6,146 — 6,146 Available-for-sale securities — U.S. government securities — 117,374 — 117,374 Available-for-sale securities — U.S. government agency securities — 47,151 — 47,151 Long-term investments Available-for-sale securities — corporate bonds and notes — 102,939 — 102,939 Total $ 43,553 $ 670,689 $ — $ 714,242 The Company uses the fair value hierarchy for financial assets and liabilities. The carrying amounts of other current financial assets and other current financial liabilities approximate fair value due to their short-term nature. Assets Measured and Recorded at Fair Value on a Non-Recurring Basis The Company’s non-financial assets and liabilities, which include goodwill, intangible assets, and long-lived assets, are not required to be carried at fair value on a recurring basis. These non-financial assets and liabilities are measured at fair value on a non-recurring basis when there is an indicator of impairment, and they are recorded at fair value only when impairment is recognized. The Company reviews goodwill for impairment annually, during the second quarter of each fiscal year, or as circumstances indicate the possibility of impairment. The Company monitors the carrying value of tangible and intangible long-lived assets for impairment whenever events or changes in circumstances indicate its carrying amount may not be recoverable. Included in the Company’s impairment considerations for non-financial assets and liabilities in the periods presented were the potential impacts of the COVID-19 pandemic. During the year ended September 30, 2021, the Company recorded an impairment of $23.5 million against the operating lease right-of-use asset related to the permanent exit of six floors in its corporate headquarters and $10.3 million for tenant improvements and other fixed assets associated with the exited floors. The Company also recorded an impairment of $6.7 million against the operating lease right-of-use asset related to the integration of the former Shape headquarters in Santa Clara, California and $0.2 million for other fixed assets associated with the impaired Shape headquarters. During the year ended September 30, 2020, the Company recorded impairment of a right-of-use asset of $9.7 million related to the former Seattle headquarters location, due to the low likelihood of future sublease receipts, as the Company will no longer seek to sublease the space. The Company calculated the fair value of the right-of-use assets, tenant improvements and other fixed assets based on estimated future discounted cash flows and classified the fair value as a Level 3 measurement due to the significance of unobservable inputs, which included the amount and timing of estimated sublease rental receipts that the Company could reasonably obtain over the remaining lease term and the discount rate. The impairment charges for the year ended September 30, 2021 and 2020 were allocated to various expense line items on the Company’s consolidated income statements based on the teams that previously worked out of the exited space. During the year ended September 30, 2019, the Company recorded impairment of capitalized internal-use software costs of $6.3 million, which was reflected in the general and administrative expense line item on the Company's consolidated income statement. Impairment charges were allocated to the following income statement line items for the years ended September 30, 2021, 2020, and 2019 (in thousands): Years Ended September 30, 2021 2020 2019 Cost of net product revenue $ 2,865 $ 241 $ — Cost of net service revenue 3,492 1,034 — Sales and marketing 11,515 2,876 — Research and development 12,974 2,906 — General and administrative 9,852 2,616 6,273 Total impairment charges $ 40,698 $ 9,673 $ 6,273 During the years ended September 30, 2021, 2020, and 2019, the Company did not recognize any impairment charges related to goodwill or other intangible assets.

Short-Term And Long-Term Invest

Short-Term And Long-Term Investments	12 Months Ended
	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Short-Term And Long-Term Investments	Short-Term and Long-Term Investments Short-term investments consist of the following (in thousands): September 30, 2021 Cost or Gross Gross Fair Value Certificates of deposit $ 255 $ — $ — $ 255 Corporate bonds and notes 186,043 116 (52) 186,107 Municipal bonds and notes 13,570 1 (5) 13,566 U.S. government securities 102,607 12 (4) 102,615 U.S. government agency securities 27,096 — (9) 27,087 $ 329,571 $ 129 $ (70) $ 329,630 September 30, 2020 Cost or Gross Gross Fair Value Corporate bonds and notes $ 188,932 $ 736 $ (6) $ 189,662 Municipal bonds and notes 6,143 3 — 6,146 U.S. government securities 117,363 14 (3) 117,374 U.S. government agency securities 47,148 3 — 47,151 $ 359,586 $ 756 $ (9) $ 360,333 Long-term investments consist of the following (in thousands): September 30, 2021 Cost or Gross Gross Fair Value Corporate bonds and notes $ 53,128 $ 13 $ (34) $ 53,107 Municipal bonds and notes 11,114 1 (4) 11,111 U.S. government securities 59,614 2 (8) 59,608 U.S. government agency securities 8,957 — (5) 8,952 $ 132,813 $ 16 $ (51) $ 132,778 September 30, 2020 Cost or Gross Gross Fair Value Corporate bonds and notes $ 102,206 $ 756 $ (23) $ 102,939 $ 102,206 $ 756 $ (23) $ 102,939 Interest income from investments was $2.5 million, $12.2 million and $25.3 million for fiscal years 2021, 2020 and 2019, respectively. Interest income is included in other (expense) income, net on the Company's consolidated income statements. The following table summarizes investments that have been in a continuous unrealized loss position for less than 12 months and those that have been in a continuous unrealized loss position for more than 12 months as of September 30, 2021 (in thousands): Less Than 12 Months 12 Months or Greater Total September 30, 2021 Fair Value Gross Fair Gross Fair Value Gross Corporate bonds and notes $ 151,986 $ (86) $ — $ — $ 151,986 $ (86) Municipal bonds and notes 13,764 (9) — — 13,764 (9) U.S. government securities 77,401 (12) — — 77,401 (12) U.S. government agency securities 31,384 (14) — — 31,384 (14) Total $ 274,535 $ (121) $ — $ — $ 274,535 $ (121) The following table summarizes investments that have been in a continuous unrealized loss position for less than 12 months and those that have been in a continuous unrealized loss position for more than 12 months as of September 30, 2020 (in thousands): Less Than 12 Months 12 Months or Greater Total September 30, 2020 Fair Value Gross Fair Value Gross Fair Value Gross Corporate bonds and notes $ 43,492 $ (28) $ 5,006 $ (1) $ 48,498 $ (29) U.S. government securities 41,812 (3) — — 41,812 (3) Total $ 85,304 $ (31) $ 5,006 $ (1) $ 90,310 $ (32) The Company invests in securities that are rated investment grade. The Company reviews the individual securities in its portfolio to determine whether a credit loss exists by comparing the extent to which the fair value is less than the amortized cost and considering any changes to ratings of a security by a ratings agency. The Company determined that as of September 30, 2021, there were no credit losses on any investments within its portfolio.

Balance Sheet Details

Balance Sheet Details	12 Months Ended
	Sep. 30, 2021
Balance Sheet Details [Abstract]
Balance Sheet Details	Balance Sheet Details Cash, Cash Equivalents and Restricted Cash The following table provides a reconciliation of the Company’s cash and cash equivalents and restricted cash reported within the consolidated balance sheets that sum to the total cash, cash equivalents and restricted cash shown in the Company’s consolidated statements of cash flows for the periods presented (in thousands): September 30, 2021 2020 Cash and cash equivalents $ 580,977 $ 849,556 Restricted cash included in other assets, net 3,356 3,270 Total cash, cash equivalents and restricted cash $ 584,333 $ 852,826 Inventories Inventories consist of the following (in thousands): September 30, 2021 2020 Finished goods $ 13,081 $ 17,096 Raw materials 8,974 10,802 $ 22,055 $ 27,898 Other Current Assets Other current assets consist of the following (in thousands): September 30, 2021 2020 Unbilled receivables $ 215,396 $ 138,096 Prepaid expenses 59,636 47,197 Capitalized contract acquisition costs 34,265 29,650 Other 28,605 44,563 $ 337,902 $ 259,506 Property and Equipment Property and equipment consist of the following (in thousands): September 30, 2021 2020 Computer equipment $ 166,846 $ 153,256 Software 94,169 95,288 Office furniture and equipment 45,204 45,280 Leasehold improvements 174,504 175,593 480,723 469,417 Accumulated depreciation and amortization (289,559) (240,178) $ 191,164 $ 229,239 Depreciation and amortization expense totaled approximately $61.3 million, $59.5 million, and $58.0 million for the fiscal years ended September 30, 2021, 2020 and 2019, respectively. During the year ended September 30, 2021, the Company recorded an impairment of $10.3 million for leasehold improvements and other fixed assets associated with the permanent exit of six floors in its corporate headquarters. The Company also recorded an impairment of $0.2 million for fixed assets associated with the integration of the former Shape headquarters in Santa Clara, California. The impairment charges for the year ended September 30, 2021 were allocated to various expense line items on the Company’s consolidated income statements based on the teams that previously worked out of the exited space. During the year ended September 30, 2019, the Company recorded impairment of capitalized internal-use software costs of $6.3 million, which was reflected in the general and administrative expense line item on the Company's consolidated income statement. Goodwill Changes in the carrying amount of goodwill during fiscal years 2021 and 2020 are summarized as follows (in thousands): Balance, September 30, 2019 $ 1,065,379 Acquisition of Shape Security, Inc. 799,611 Other (6,024) Balance, September 30, 2020 1,858,966 Acquisition of Volterra, Inc. 351,417 Other 6,170 Balance, September 30, 2021 $ 2,216,553 Other Assets Other assets consist of the following (in thousands): September 30, 2021 2020 Intangible assets $ 237,178 $ 225,900 Unbilled receivables 158,885 62,377 Capitalized contract acquisition costs 43,571 40,746 Other 32,924 18,424 $ 472,558 $ 347,447 Intangible assets are included in other assets on the balance sheet and consist of the following (in thousands): September 30, 2021 September 30, 2020 Gross Accumulated Net Carrying Gross Accumulated Net Carrying Developed technology $ 305,673 $ (111,279) $ 194,394 $ 246,173 $ (76,556) $ 169,617 Customer relationships 41,742 (17,865) 23,877 41,242 (10,657) 30,585 Patents and trademarks 20,260 (17,180) 3,080 20,260 (14,448) 5,812 Trade names 24,973 (9,146) 15,827 24,973 (5,174) 19,799 Non-compete covenants 2,260 (2,260) — 2,260 (2,173) 87 $ 394,908 $ (157,730) $ 237,178 $ 334,908 $ (109,008) $ 225,900 Amortization expense related to intangible assets was approximately $48.7 million, $34.6 million, and $11.8 million for the fiscal years ended September 30, 2021, 2020 and 2019, respectively. For intangible assets held as of September 30, 2021, amortization expense for the five succeeding fiscal years is as follows (in thousands): 2022 $ 50,095 2023 49,125 2024 43,860 2025 38,124 2026 32,860 $ 214,064 Accrued Liabilities Accrued liabilities consist of the following (in thousands): September 30, 2021 2020 Payroll and benefits $ 179,147 $ 169,708 Operating lease liabilities, current 49,286 46,010 Income and other tax accruals 44,075 33,048 Other 68,979 72,632 $ 341,487 $ 321,398 Other Long-term Liabilities Other long-term liabilities consist of the following (in thousands): September 30, 2021 2020 Income taxes payable $ 66,081 $ 49,846 Other 9,155 9,665 $ 75,236 $ 59,511

Debt Facilities

Debt Facilities	12 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Debt Facilities	Debt Facilities Term Credit Agreement In connection with the acquisition of Shape, on January 24, 2020, the Company entered into a Term Credit Agreement ("Term Credit Agreement") with certain institutional lenders that provides for a senior unsecured term loan facility in an aggregate principal amount of $400.0 million (the "Term Loan Facility"). The proceeds from the Term Loan Facility were primarily used to finance the acquisition of Shape and related expenses. In connection with the Term Loan Facility, the Company incurred $2.2 million in debt issuance costs, which are recorded as a reduction to the carrying value of the principal amount of the debt. Borrowings under the Term Loan Facility bear interest at a rate equal to, at the Company's option, (a) LIBOR, adjusted for customary statutory reserves, plus an applicable margin of 1.125% to 1.75% depending on the Company's leverage ratio, or (b) an alternate base rate determined in accordance with the Term Credit Agreement, plus an applicable margin of 0.125% to 0.750% depending on the Company's leverage ratio. Interest on the outstanding principal of borrowings is currently due quarterly in arrears. As of September 30, 2021, the margin for LIBOR-based loans was 1.125% and the margin for alternate base rate loans was 0.125%. The Term Loan Facility matures on January 24, 2023 with quarterly installments (commencing with the first full fiscal quarter ended after January 24, 2020) equal to 1.25% of the original principal amount of the Term Loan Facility. The remaining outstanding principal of borrowings under the Term Loan Facility is due upon maturity on January 24, 2023. Borrowings under the Term Loan Facility may be voluntarily prepaid, in whole or in part, without penalty or premium. Borrowings repaid or prepaid under the Term Loan Facility may not be reborrowed. Among certain affirmative and negative covenants provided in the Term Credit Agreement, there is a financial covenant that requires the Company to maintain a leverage ratio, calculated as of the last day of each fiscal quarter, of consolidated total indebtedness to consolidated EBITDA. This covenant may result in a higher interest rate on its outstanding principal borrowings on the Term Loan Facility in future periods, depending on the Company's performance. As of September 30, 2021, the Company was in compliance with all covenants. As of September 30, 2021, $370.0 million of principal amount under the Term Loan Facility was outstanding, excluding unamortized debt issuance costs of $1.0 million. The weighted average interest rate on the principal amount under the Term Loan Facility outstanding balance was 1.361% and 2.365% for the fiscal years ended September 30, 2021 and 2020, respectively. The following table presents the scheduled principal maturities as of September 30, 2021 (in thousands): Fiscal Years Ending September 30: 2022 $ 20,000 2023 350,000 Total $ 370,000 Revolving Credit Agreement On January 31, 2020, the Company entered into a Revolving Credit Agreement (the "Revolving Credit Agreement") that provides for a senior unsecured revolving credit facility in an aggregate principal amount of $350.0 million (the "Revolving Credit Facility"). The Company has the option to increase commitments under the Revolving Credit Facility from time to time, subject to certain conditions, by up to $150.0 million. Borrowings under the Revolving Credit Facility bear interest at a rate equal to, at the Company's option, (a) LIBOR, adjusted for customary statutory reserves, plus an applicable margin of 1.125% to 1.75% depending on the Company's leverage ratio, or (b) an alternate base rate determined in accordance with the Revolving Credit Agreement, plus an applicable margin of 0.125% to 0.750% depending on the Company's leverage ratio. The Revolving Credit Agreement also requires payment of a commitment fee calculated at a rate per annum of 0.125% to 0.300% depending on the Company's leverage ratio on the undrawn portion of the Revolving Credit Facility. Commitment fees incurred during fiscal year 2021 were not material.

Leases

Leases	12 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Leases	Leases During the first quarter of fiscal 2020, the Company adopted ASU 2016-02, Leases (Topic 842) (the "Leasing Standard") on a modified retrospective basis using the transition method provided in ASU 2018-11, Leases (Topic 842): Targeted Improvements . The impact of adopting the Leasing Standard resulted in the recognition of right-of-use assets and lease liabilities of $304.8 million and $386.4 million, respectively, on October 1, 2019, the date of adoption. The majority of the Company's operating lease payments relate to its corporate headquarters in Seattle, Washington, which includes approximately 515,000 square feet of office space. The lease commenced in April 2019 and expires in 2033 with an option for renewal. The Company also leases additional office and lab space for product development and sales and support personnel in the United States and internationally. The Company's lease agreements do not contain any material residual value guarantees or material restrictive covenants. The components of the Company's operating lease expenses for the years ended September 30, 2021 and 2020 were as follows (in thousands): Fiscal year ended September 30, 2021 2020 Operating lease expense $ 47,993 $ 49,925 Short-term lease expense 2,953 3,563 Variable lease expense 25,200 21,980 Total lease expense $ 76,146 $ 75,468 Variable lease expense primarily consists of common area maintenance and parking expenses. Supplemental balance sheet information related to the Company's operating leases was as follows (in thousands, except lease term and discount rate): September 30, 2021 2020 Operating lease right-of-use assets, net $ 244,934 $ 300,680 Operating lease liabilities, current 1 49,286 46,010 Operating lease liabilities, long-term 296,945 338,715 Total operating lease liabilities $ 346,231 $ 384,725 Weighted average remaining lease term (in years) 9.7 10.2 Weighted average discount rate 2.60 % 2.58 % (1) Current portion of operating lease liabilities is included in accrued liabilities on the Company's consolidated balance sheets. As of September 30, 2021, the future operating leases payments for each of the next five years and thereafter is as follows (in thousands): Fiscal Years Ending September 30: Operating Lease 2022 $ 57,849 2023 48,458 2024 41,142 2025 33,600 2026 26,609 Thereafter 191,142 Total lease payments 398,800 Less: imputed interest (52,569) Total lease liabilities $ 346,231 Operating lease liabilities above do not include sublease income. As of September 30, 2021, the Company expects to receive sublease income of approximately $13.0 million, which consists of $5.7 million to be received in fiscal year 2022 and $7.3 million to be received over the three fiscal years thereafter. During the year ended September 30, 2021, the Company recorded an impairment of $23.5 million against the operating lease right-of-use asset related to the exit of six floors in its corporate headquarters. The Company also recorded an impairment of $6.7 million against the right-of-use asset related to the integration of the former Shape headquarters in Santa Clara, California. During the year ended September 30, 2020, the Company recorded an impairment for $9.7 million against the right-of-use asset related to the former Seattle headquarters location, due to the low likelihood of future sublease receipts, as the Company will no longer seek to sublease the space. As of September 30, 2021, the Company had no significant operating leases that were executed but not yet commenced. ASC 840 - Leases As a result of adopting the Leasing Standard, reporting periods beginning in the first quarter of fiscal 2020 are presented under the new standard while prior period amounts are not adjusted and continue to be reported in accordance with ASC 840 - Leases. Prior to the adoption of the Leasing Standard, future minimum operating lease payments, net of sublease income, were as follows as of September 30, 2019 (in thousands): Fiscal Year Gross Lease Sublease Net Lease 2020 $ 54,046 $ 683 $ 53,363 2021 50,712 1,051 49,661 2022 47,550 1,082 46,468 2023 36,514 368 36,146 2024 33,971 — 33,971 Thereafter 242,826 — 242,826 $ 465,619 $ 3,184 $ 462,435

Income Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The United States and international components of income before income taxes are as follows (in thousands): Years Ended September 30, 2021 2020 2019 United States $ 189,398 $ 216,409 $ 360,648 International 197,539 179,988 180,463 $ 386,937 $ 396,397 $ 541,111 The provision for income taxes consists of the following (in thousands): Years Ended September 30, 2021 2020 2019 Current U.S. federal $ 53,107 $ 26,978 $ 43,039 State 16,686 4,230 13,864 Foreign 62,832 50,368 49,197 Total 132,625 81,576 106,100 Deferred U.S. federal (61,739) 10,875 8,716 State (15,294) (1,121) 1,617 Foreign 104 (2,374) (3,056) Total (76,929) 7,380 7,277 $ 55,696 $ 88,956 $ 113,377 The effective tax rate differs from the U.S. federal statutory rate as follows (in thousands): Years Ended September 30, 2021 2020 2019 Income tax provision at statutory rate $ 81,257 $ 83,243 $ 113,633 State taxes, net of federal benefit 5,118 4,258 14,206 Tax impact of foreign operations (26,881) (7,693) (9,161) Research and development and other credits (18,055) (11,843) (12,760) Stock-based and other compensation 12,740 18,002 6,771 Other 1,517 2,989 688 $ 55,696 $ 88,956 $ 113,377 Effective January 1, 2018, the U.S. tax law provides a deduction for the foreign-source portion of dividends received from specified foreign corporations. The Company no longer maintains an indefinite reinvestment assertion on unremitted foreign earnings and has recorded a deferred tax liability for any estimated foreign, federal, or state tax liabilities associated with a future repatriation of foreign earnings. The Company benefits from tax incentive arrangements in certain foreign jurisdictions, one of which expired in fiscal year 2021 and the rest of which expire in fiscal years 2022 to 2034. The tax incentive agreements are conditional upon meeting certain operational, employment, and investment requirements. These arrangements decreased foreign taxes by $6.0 million, $8.2 million and $8.1 million, and increased diluted earnings per common share by $0.10, $0.13 and $0.13 for the years ended September 30, 2021, 2020 and 2019, respectively. The tax effects of the temporary differences that give rise to the deferred tax assets and liabilities are as follows (in thousands): Years Ended September 30, 2021 2020 Deferred tax assets Net operating loss carry-forwards $ 41,252 $ 54,842 Capitalized research and development costs 95,259 — Accrued compensation and benefits 13,207 13,162 Stock-based compensation 12,829 13,010 Deferred revenue 30,115 40,577 Lease liabilities 23,747 19,656 Other accruals and reserves 18,450 17,384 Tax credit carryforwards 34,187 15,807 Depreciation 580 620 269,626 175,058 Valuation allowance (40,404) (32,587) 229,222 142,471 Deferred tax liabilities Purchased intangibles (57,219) (46,491) Depreciation (26,516) (34,757) Deferred costs (13,057) (11,924) Other accruals and reserves (6,651) (4,728) (103,443) (97,900) Net deferred tax assets $ 125,779 $ 44,571 At September 30, 2021, the Company had foreign net operating loss carryforwards of approximately $61.3 million that can be carried forward indefinitely, and $2.7 million that will expire in fiscal year 2026. The Company had $92.8 million of federal net operating loss carryforwards, of which $82.9 million can be carried forward indefinitely and $9.9 million that will expire in fiscal years 2032 to 2035. The annual utilization of the federal net operating loss carryforwards is limited under Internal Revenue Code Section 382. The Company also had $476.1 million of state net operating loss carryforwards, of which $292.0 million can be carried forward indefinitely and $184.1 million will expire in fiscal years 2033 to 2040. In addition, there are $3.3 million of foreign credit carryforwards that will expire in fiscal years 2022 to 2037, $9.5 million of federal credit carryforwards that will expire in fiscal years 2033 to 2040, $25.7 million of state tax credit carryforwards that can be carried forward indefinitely, and $3.3 million of state tax credit carryforwards that will expire in fiscal years 2031 to 2036. Management believes that it is more likely than not that the benefit from certain foreign net operating loss and credit carryforwards and state tax net operating loss and credit carryforwards will not be realized. In recognition of this risk, the Company has provided a valuation allowance on the deferred tax assets relating to these carryforwards. The net change in the total valuation allowance was an increase of $7.8 million and $9.1 million for years ended September 30, 2021 and 2020, respectively. The Company recognizes the financial statement impact of a tax position only after determining that the relevant tax authority would more likely than not sustain the position following an audit. For tax positions meeting the more-likely-than-not threshold, the amount recognized in the financial statements is the largest impact that has a greater than fifty percent likelihood of being realized upon ultimate settlement with the relevant tax authority. The following table provides a reconciliation of the beginning and ending amount of unrecognized tax benefits in fiscal years 2021, 2020 and 2019 (in thousands): 2021 2020 2019 Balance, beginning of period $ 51,767 $ 42,287 $ 31,672 Gross increases related to prior period tax positions 14,867 8,664 5,129 Gross decreases related to prior period tax positions — (1,051) (287) Gross increases related to current period tax positions 12,595 9,272 7,756 Decreases relating to settlements with tax authorities (321) (3,578) — Reductions due to lapses of statute of limitations (8,094) (3,827) (1,983) Balance, end of period $ 70,814 $ 51,767 $ 42,287 The total amount of gross unrecognized tax benefits was $70.8 million, $51.8 million, and $42.3 million as of September 30, 2021, 2020, and 2019, respectively, of which, $39.2 million, $34.3 million, and $29.4 million, if recognized, would affect the effective tax rate. There is a reasonable possibility that the Company’s unrecognized tax benefits will change within twelve months due to audit settlements or the expiration of statute of limitations, but the Company does not expect the change to be material to the consolidated financial statements. The Company recognizes interest and, if applicable, penalties (not included in the “unrecognized tax benefits” table above) for any uncertain tax positions. Interest and penalties are recorded as a component of income tax expense. In the years ended September 30, 2021, 2020 and 2019, the Company recorded approximately a $1.4 million increase, $1.0 million decrease and $2.4 million increase, respectively, of interest and penalty expense related to uncertain tax positions. As of September 30, 2021 and 2020, the Company had a cumulative balance of accrued interest and penalties on unrecognized tax positions of $4.4 million and $3.0 million, respectively. The Company and its subsidiaries are subject to U.S. federal income tax as well as the income tax of multiple state and foreign jurisdictions. The Company has concluded all U.S. federal income tax matters for fiscal years through September 30, 2017. Major jurisdictions where there are wholly owned subsidiaries of F5, Inc. which require income tax filings include the United Kingdom, Singapore, and Israel. The earliest periods open for review by local taxing authorities are fiscal years 2020 for the United Kingdom, 2016 for Singapore, and 2013 for Israel. The Company is currently under audit by various states for fiscal years 2015 through 2019 and by various foreign jurisdictions including Israel for fiscal years 2013 to 2018, Saudi Arabia for fiscal years 2015 to 2020, Singapore for fiscal year 2018, and India for fiscal years 2019 to 2020. Within the next four fiscal quarters, the statute of limitations will begin to close on the fiscal year 2018 federal income tax return, fiscal years 2016, 2017, and 2018 state income tax returns and fiscal years 2014 to 2020 foreign income tax returns.

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Stockholders' Equity	Shareholders' Equity Common Stock Repurchase On October 31, 2018, the Company announced that its Board of Directors authorized an additional $1.0 billion for its common stock share repurchase program. This authorization is incremental to the existing $4.4 billion program, initially approved in October 2010 and expanded in each fiscal year thereafter. Acquisitions for the share repurchase programs will be made from time to time in private transactions, accelerated share repurchase programs, or open market purchases as permitted by securities laws and other legal requirements. The programs can be terminated at any time. On February 3, 2021, the Company entered into Accelerated Share Repurchase (ASR) agreements with two financial institutions under which the Company paid an aggregate of $500 million. The ASR agreements were accounted for as two separate transactions (1) a repurchase of common stock and (2) an equity-linked contract on the Company's own stock. Upon execution of the ASR agreements, the Company received an initial delivery of 2.1 million shares for an aggregate price of $400 million, based on the market price of $194.91 per share of the Company's common stock on the date of the transaction. The initial shares received by the Company were retired immediately upon receipt. The equity-linked contract for the remaining $100 million, representing remaining shares to be delivered by the financial institutions under the ASR agreements, was recorded to common stock as of March 31, 2021 and was settled in the third quarter of fiscal 2021 with the Company receiving 449,049 additional shares, which were retired immediately upon receipt. The total ASR resulted in a repurchase of 2.5 million shares of the Company's common stock at a volume weighted average repurchase price, less an agreed upon discount, of $199.90 per share. The shares received by the Company were retired, accounted for as a reduction to stockholder’s equity in the Condensed Consolidated Balance Sheets, and treated as a repurchase of common stock for purposes of calculating earnings per share. The Company was not required to make any additional cash payments or delivery of common stock to the financial institutions upon settlement of the agreements. As of September 30, 2021, the Company had $773 million remaining authorized to purchase shares under its share repurchase program.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement, Noncash Expense [Abstract]
Stock-Based Compensation	Stock-based Compensation The Company recognized $243.3 million, $201.9 million and $162.9 million of stock-based compensation expense for the fiscal years ended September 30, 2021, 2020 and 2019, respectively. The income tax benefit recognized on stock-based compensation within income tax expense was $44.1 million, $37.6 million and $31.3 million for the fiscal years ended September 30, 2021, 2020 and 2019, respectively. As of September 30, 2021, there was $220.7 million of total unrecognized stock-based compensation cost, the majority of which will be recognized over approximately two years. Going forward, stock-based compensation expenses may increase as the Company issues additional equity-based awards to continue to attract and retain key employees. On October 29, 2021, the Company’s Board of Directors and Talent and Compensation Committee approved 881,908 RSUs to employees and executive officers pursuant to the Company’s annual equity awards program. Company has adopted a number of stock-based compensation plans as discussed below. 2011 Employee Stock Purchase Plan. In April 2012, the Board of Directors amended and restated the Company’s 1999 Employee Stock Purchase Plan, or the Employee Stock Purchase Plan. A total of 10,000,000 shares of common stock have been reserved for issuance under the Employee Stock Purchase Plan. The Employee Stock Purchase Plan permits eligible employees to acquire shares of the Company’s common stock through periodic payroll deductions of up to 15% of base compensation. No employee may purchase more than 10,000 shares during an offering period. In addition, no employee may purchase more than $25,000 worth of stock, determined by the fair market value of the shares at the time such option is granted, in one calendar year. The Employee Stock Purchase Plan has been implemented in a series of offering periods, each 6 months in duration. The price at which the common stock may be purchased is 85% of the lesser of the fair market value of the Company’s common stock on the first day of the applicable offering period or on the last day of the respective purchase period. As of September 30, 2021 there were 1,356,896 shares available for awards under the Employee Stock Purchase Plan. In determining the fair value of the right to purchase under the Employee Stock Purchase Plan, the Company uses the Black-Scholes option pricing model that employs the following key assumptions: Employee Stock Purchase Plan 2021 2020 2019 Risk-free interest rate 0.07% - 0.13% 1.10% - 1.97% 2.25% - 2.51% Expected dividend — — — Expected term 0.5 years 0.5 years 0.5 years Expected volatility 29.67% - 37.22% 26.32% - 41.94% 18.14% - 31.74% Acquisition Related Incentive Plans. In connection with the Company’s acquisition of Traffix Systems in the second quarter of fiscal year 2012, the Company assumed the Traffix 2007 Israeli Employee Share Option Plan, or the Traffix Plan. Unvested options to acquire Traffix’s common stock were converted into options to acquire the Company’s common stock in connection with the acquisition. A total of 106,829 shares of common stock were reserved for issuance under the Traffix Plan. The plan provided for grants of stock options to persons who were employees, officers, directors, consultants or advisors to Traffix on or prior to February 21, 2012. During the fiscal year 2021, the Company issued no stock options or restricted stock units under the Traffix Plan. As of September 30, 2021, there were options to purchase 49 shares outstanding and no shares available for additional awards under the Traffix Plan. The Company terminated the Traffix Plan effective January 3, 2014 and no additional shares may be issued from the Traffix Plan. In May 2019, the Company adopted the Nginx Acquisition Equity Incentive Plan, or the Nginx Acquisition Plan. The Nginx Acquisition Plan provided for discretionary grants of stock options and stock units for employees, directors and consultants of Nginx, Inc. to whom the Company offered employment in connection with the Company’s acquisition of Nginx. A total of 183,061 shares of common stock were reserved for issuance under the Nginx Acquisition Plan. Upon certain changes in control of the Company, the surviving entity will either assume or substitute all outstanding stock awards under the Nginx Acquisition Plan or the vesting of 50% of the stock awards shall be accelerated. During the fiscal year 2021, the Company issued no stock options or restricted stock units under the Nginx Acquisition Plan. As of September 30, 2021, there were no options outstanding and 71,302 stock units outstanding. The Company terminated the Nginx Acquisition Plan effective October 31, 2019 and no additional shares may be issued from the Nginx Acquisition Plan. In connection with the Company’s acquisition of Nginx, Inc. in the third quarter of fiscal year 2019, the Company assumed the Nginx Inc. 2011 Share Plan, or the Nginx Plan. Unvested options to acquire Nginx's common stock and unvested stock units with respect to Nginx’s common stock were converted into options to acquire the Company’s common stock and stock units with respect to the Company’s stock in connection with the acquisition. A total of 302,634 shares of common stock were reserved for issuance under the Nginx Plan (including converted options and stock units). The Nginx Plan provided for grants of stock options, stock awards and stock units to persons who were employees, officers, directors and consultants to Nginx, Inc. prior to May 8, 2019. During the fiscal year 2021, the Company issued no stock options or restricted stock units under the Nginx Plan. As of September 30, 2021, there were options to purchase 68,095 shares outstanding and 9,242 stock units outstanding. The Company terminated the Nginx Plan effective October 31, 2019 and no additional shares may be issued from the Nginx Plan. In January 2020, the Company adopted the Shape Acquisition Equity Incentive Plan, or the Shape Acquisition Plan. The Shape Acquisition Plan provided for discretionary grants of stock options and stock units for employees, directors and consultants of Shape Security, Inc. to whom the Company offered employment in connection with the Company’s acquisition of Shape. A total of 450,000 shares of common stock were reserved for issuance under the Shape Acquisition Plan. Upon certain changes in control of the Company, the surviving entity will either assume or substitute all outstanding stock awards under the Shape Acquisition Plan or the vesting of 50% of the stock awards shall be accelerated. During the fiscal year 2021, the Company issued no stock options or restricted stock units under the Shape Acquisition Plan. As of September 30, 2021, there were no options outstanding and 210,720 stock units outstanding. The Company terminated the Shape Acquisition Plan effective December 28, 2020 and no additional shares may be issued from the Shape Acquisition Plan. In connection with the Company’s acquisition of Shape Security, Inc. in the second quarter of fiscal year 2020, the Company assumed the Shape 2011 Stock Plan, or the Shape Plan. Unvested options to acquire Shape’s common stock and unvested stock units with respect to Shape’s common stock were converted into options to acquire the Company’s common stock and stock units with respect to the Company’s stock in connection with the acquisition. A total of 501,085 shares of common stock were reserved for issuance under the Shape Plan (including converted options and stock units). The Shape Plan provided for grants of stock options, stock awards and stock units to persons who were employees, officers, directors and consultants to Shape Security, Inc. prior to January 24, 2020. During the fiscal year 2021, the Company issued no stock options or restricted stock units under the Shape Plan. As of September 30, 2021, there were options to purchase 140,033 shares outstanding and 3,755 stock units outstanding. The Company terminated the Shape Plan effective December 28, 2020 and no additional shares may be issued from the Shape Plan. In January 2021, the Company adopted the Volterra Acquisition Equity Incentive Plan, or the Volterra Acquisition Plan. The Volterra Acquisition Plan provided for discretionary grants of stock options and stock units for employees, directors and consultants of Volterra, Inc. to whom the Company offered employment in connection with the Company’s acquisition of Volterra. A total of 140,000 shares of common stock were reserved for issuance under the Volterra Acquisition Plan. Upon certain changes in control of the Company, the surviving entity will either assume or substitute all outstanding stock awards under the Volterra Acquisition Plan or the vesting of 50% of the stock awards shall be accelerated. During the fiscal year 2021, the Company issued no stock options and 122,056 restricted stock units under the Volterra Acquisition Plan. As of September 30, 2021, there were no options outstanding and 121,036 stock units outstanding. The Company terminated the Volterra Acquisition Plan effective October 29, 2021 and no additional shares may be issued from the Volterra Acquisition Plan. In connection with the Company’s acquisition of Volterra, Inc. in the second quarter of fiscal year 2021, the Company assumed the Volterra 2017 Stock Plan, or the Volterra Plan. Unvested options to acquire Shape’s common stock and unvested stock units with respect to Volterra’s common stock were converted into options to acquire the Company’s common stock and stock units with respect to the Company’s stock in connection with the acquisition. A total of 261,696 shares of common stock were reserved for issuance under the Volterra Plan (including converted options and stock units). The Volterra Plan provided for grants of stock options, stock awards and stock units to persons who were employees, officers, directors and consultants to Volterra, Inc. prior to January 22, 2021. During the fiscal year 2021, the Company issued (including conversions to Company awards) 145,360 stock options and 44,846 stock units under the Volterra Plan. As of September 30, 2021, there were options to purchase 116,447 shares outstanding and 34,863 stock units outstanding. The Company terminated the Volterra Plan effective October 29, 2021 and no additional shares may be issued from the Volterra Plan. 2014 Incentive Plan. In March 2014, the Company adopted the 2014 Incentive Plan, or the 2014 Plan, which amended and restated the 2005 Equity Incentive Plan. The 2014 Plan provides for discretionary grants of stock options, stock units and other equity and cash-based awards for employees, including officers, directors and consultants. A total of 22,180,000 shares of common stock have been reserved for issuance under the 2014 Plan. Upon certain changes in control of the Company, all outstanding and unvested options or stock awards under the 2014 Plan will vest at the rate of 50%, unless assumed or substituted by the acquiring entity. During the fiscal year 2021, the Company issued no stock options, 153,434 performance stock units and 1,510,829 restricted stock units under the 2014 Plan. As of September 30, 2021, there were no options outstanding, 230,926 performance stock units outstanding, 1,340,548 restricted stock units outstanding and 1,889,511 shares available for new awards under the 2014 Plan. A summary of restricted stock unit activity under the 2014 Plan is as follows: Performance Stock Units Restricted Stock Units Outstanding Weighted Outstanding Weighted Balance, September 30, 2020 145,869 $ 146.42 1,204,290 $ 146.39 Units granted 153,434 117.16 1,510,829 137.33 Units vested (59,365) 137.13 (1,183,086) 183.01 Units cancelled (9,012) 162.72 (191,485) 138.09 Balance, September 30, 2021 230,926 $ 136.47 1,340,548 $ 141.90 A majority of the restricted stock units the Company grants to its employees vest quarterly over a two Expected Volatility Fair Value Expected Term Risk-Free Index Expected Grant Date per Share (in years) Interest Rate F5 Members Dividend November 2, 2020 Tranche 1 $ 182.01 0.91 0.13 % 41.89 % 53.54 % — Tranche 2 $ 185.86 1.91 0.16 % 34.77 % 41.85 % — Tranche 3 $ 189.57 2.91 0.20 % 31.74 % 37.45 % — As of September 30, 2021, the following annual equity grants for executive officers or a portion thereof are outstanding: Grant Date RSUs Granted Vesting Schedule Vesting Period Date Fully Vested November 2, 2020 257,568 Quarterly, Annually 1 3 years November 1, 2023 November 1, 2019 228,616 Quarterly, Annually 1 3 years November 1, 2022 November 1, 2018 144,066 Quarterly, Annually 1 3 years November 1, 2021 November 1, 2017 140,135 Quarterly, Annually 1 4 years November 1, 2021 (1) 50% of the annual equity grant vests in equal quarterly increments and 50% is subject to the Company achieving specified annual performance goals. A summary of stock option activity under all of the Company’s plans is as follows: Options Outstanding Number of Weighted Balance, September 30, 2020 391,100 $ 36.71 Options granted 145,360 14.84 Options exercised (163,880) 29.68 Options cancelled (47,956) 34.21 Balance, September 30, 2021 324,624 $ 30.83 All stock options granted in fiscal years 2021, 2020 and 2019 were replacement awards of those assumed as part of the acquisitions of Volterra, Shape and NGINX, respectively. The total intrinsic value of options exercised during fiscal 2021, 2020 and 2019 was $25.6 million, $11.4 million and $0.7 million, respectively. A summary of options outstanding that are exercisable and that have vested and are expected to vest as of September 30, 2021 is as follows: Number of Weighted Weighted Aggregate (In thousands) Stock options outstanding 324,624 7.19 $ 30.83 $ 54,520 Exercisable 158,544 6.67 $ 28.15 $ 27,052 Vested and expected to vest 313,777 7.16 $ 30.53 $ 52,794 (1) Aggregate intrinsic value represents the difference between the fair value of the Company’s common stock underlying these options at September 30, 2021 and the related exercise prices. As of September 30, 2021, equity based awards (including stock options and restricted stock units) are available for future issuance as follows: Awards Balance, September 30, 2020 2,714,958 Granted (1,976,525) Cancelled 299,248 Additional shares reserved (terminated), net 950,729 Balance, September 30, 2021 1,988,410

Net Income Per Share

Net Income Per Share	12 Months Ended
	Sep. 30, 2021
Net Income Per Share [Abstract]
Net Income Per Share	Net Income Per ShareBasic net income per share is computed by dividing net income by the weighted average number of common shares outstanding during the period. Diluted net income per share is computed by dividing net income by the weighted average number of common and dilutive common stock equivalent shares outstanding during the period. The Company’s nonvested restricted stock units do not have nonforfeitable rights to dividends or dividend equivalents and are not considered participating securities that should be included in the computation of earnings per share under the two-class method. The following table sets forth the computation of basic and diluted net income per share (in thousands, except per share data): Years Ended September 30, 2021 2020 2019 Numerator Net income $ 331,241 $ 307,441 $ 427,734 Denominator Weighted average shares outstanding — basic 60,707 60,911 60,044 Dilutive effect of common shares from stock options and restricted stock units 1,350 467 412 Weighted average shares outstanding — diluted 62,057 61,378 60,456 Basic net income per share $ 5.46 $ 5.05 $ 7.12 Diluted net income per share $ 5.34 $ 5.01 $ 7.08 Anti-dilutive stock-based awards excluded from the calculations of diluted earnings per share were not material for the years ended September 30, 2021, 2020 and 2019.

Commitments And Contingencies

Commitments And Contingencies	12 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	Commitments and Contingencies Purchase Obligations Purchase obligations are comprised of purchase commitments with the Company’s contract manufacturers. The agreement with the Company’s primary contract manufacturer allows them to procure component inventory on the Company’s behalf based on the Company’s production forecast. The Company is obligated to purchase component inventory that the contract manufacturer procures in accordance with the forecast, unless cancellation is given within applicable lead times. As of September 30, 2021, the Company’s remaining unfulfilled purchase obligations were $26.4 million. Litigation Lynwood Investment CY Limited v. F5 Networks et al. On June 8, 2020, Lynwood Investment CY Limited (“Lynwood”) filed a lawsuit in the United States District Court for the Northern District of California against the Company and certain affiliates, along with other defendants. In its complaint, Lynwood claims to be the assignee of all rights and interests of Rambler Internet Holding LLC (“Rambler”), and alleges that the intellectual property in the NGINX software originally released by the co-founder of NGINX in 2004 belongs to Rambler (and therefore Lynwood, by assignment) because the software was created and developed while the co-founder was employed by Rambler. Lynwood asserts 26 causes of action against the various defendants, including copyright infringement, violation of trademark law, tortious interference, conspiracy, and fraud. The complaint seeks damages, disgorgement of profits, fees and costs, declarations of copyright and trademark ownership, trademark cancellations, and injunctive relief. Lynwood also initiated several trademark opposition and cancellation proceedings before the Trademark Trial and Appeal Board of the United States Patent and Trademark Office, which have all since been suspended. In August and October 2020, the Company and the other defendants filed motions to dismiss all claims asserted against them in the lawsuit. While these motions were pending, the Court ordered Lynwood to select ten of its twenty-six claims to litigate through trial while the remaining sixteen claims would be stayed pending resolution of the ten selected claims. On March 25 and 30, 2021, the Court dismissed the ten selected claims and granted Lynwood leave to cure the deficiencies in its complaint though it expressed doubt about Lynwood’s ability to do so. The Court further ruled that Lynwood may not add new causes of action or add new parties without stipulation or leave of court, and that unless Lynwood corrects “all the defects” identified in the Court’s orders and the Company’s and other defendants’ motions to dismiss, the Court will dismiss the ten claims with prejudice. On April 6, the Court referred the parties to private mediation to be completed by June 1, 2021. Pursuant to the Court’s order, the parties held a private mediation on May 27, 2021. The matter did not resolve. On April 29, Lynwood filed its amended complaint, seeking the same relief against the Company and other defendants. On May 27, 2021, the Company and other defendants filed a consolidated motion to dismiss the claims Lynwood had selected to proceed to litigate through trial, reserving their right to move to dismiss the 16 stayed claims once the Court lifts the stay. The motion to dismiss was set to be heard by the Court on October 14, 2021, but on October 11, 2021, the Court vacated the hearing and gave notice that it will decide the motion on the papers without oral argument. Proven Networks LLC Litigations Proven Networks LLC (“Proven”) is a non-practicing entity (NPE) whose sole business is acquiring patents and filing lawsuits alleging infringement of those patents to extract licensing fees. Proven acquired a portfolio of Alcatel-Lucent patents and has asserted various patents from that portfolio against more than a dozen technology companies in courts in California and Texas, in the International Trade Commission and in foreign courts. Proven is currently pursuing three actions against the Company. In each of these cases, Management believes that the Company has strong non-infringement and invalidity defenses against the asserted patents and intends to vigorously defend these lawsuits. 1. Proven Networks, LLC v. F5 Networks, Inc. (Northern District of California and Western District of Texas) On April 13, 2020, Proven filed a lawsuit in the United States District Court for the Northern District of California against the Company alleging infringement of four U.S. patents. Prior to the Company’s response to Proven’s complaint, Proven dismissed its claims on two of the asserted patents with prejudice. For the two remaining patents, the Company filed a motion to dismiss those patents as ineligible for patenting under 35 U.S.C. Sect. 101. Prior to the California court’s decision on these motions, however, the case against the Company was moved to the Western District of Texas for pretrial proceedings along with 15 other defendants as part of a Multi-District Litigation (“MDL”). The Company intends to seek remand to the Northern District of California for the remainder of the case. Both remaining patents being asserted against the Company are subject to currently pending validity challenges in the U.S. Patent and Trademark Office’s inter partes review (“IPR”) procedure. The Company has strong non-infringement and invalidity defenses against the asserted patents. 2. Proven Networks, LLC v. F5 Networks, Inc. (International Trade Commission) On May 28, 2021, Proven filed a complaint in the International Trade Commission against the Company. In its complaint, Proven alleges that Company products – particularly the Policy Enforcement Manager (“PEM”) module - infringe a patent owned by Proven. The ITC instituted the investigation in August 2021. The trial is scheduled to begin on May 2, 2022. Management believes that the Company has strong non-infringement and invalidity defenses against the asserted patent and intends to vigorously defend this lawsuit. 3. Proven Networks, LLC v. F5 Networks, Inc. (Munich, Germany) On September 14 and 15, 2020, respectively, Proven filed two lawsuits against the Company in the Regional Court in Munich, Germany. Each suit also names a German distributor of the Company. One suit alleges infringement of the European counterpart of one of the patents previously asserted against the Company in the California and Texas cases and the other suit alleges another patent that is not involved in the California and Texas cases. In response to Proven’s infringement actions, the Company has filed nullity actions against both patents at the Federal Patent Court in Munich. An infringement hearing in the first-filed case is currently set for December 15, 2021, and an infringement hearing in the second case is set for March 8, 2022. Like the cases in the U.S., the Company believes that it has strong defenses to Proven’s claims. In addition to the above matters, the Company is subject to a variety of legal proceedings, claims, investigations, and litigation arising in the ordinary course of business, including intellectual property litigation. Management believes that the Company has meritorious defenses to the allegations made in its pending cases and intends to vigorously defend these lawsuits; however, the Company is unable currently to determine the ultimate outcome of these or similar matters or the potential exposure to loss, if any. There are many uncertainties associated with any litigation and these actions or other third-party claims against the Company may cause it to incur costly litigation and/or substantial settlement charges that could have a material adverse effect on the Company's business, financial condition, results of operations, and cash flows. The Company records an accrual for loss contingencies for legal proceedings when it believes that an unfavorable outcome is both (a) probable and (b) the amount or range of any possible loss is reasonably estimable. The Company has not recorded any accrual for loss contingencies associated with such legal proceedings or the investigations discussed above.

Restructuring Charges

Restructuring Charges	12 Months Ended
	Sep. 30, 2021
Restructuring and Related Activities [Abstract]
Restructuring Charges	Restructuring ChargesIn December 2019, the Company initiated a restructuring plan to match strategic and financial objectives and optimize resources for long term growth, including a reduction in force program affecting approximately 75 employees. The Company recorded a restructuring charge of $7.8 million in the first quarter of fiscal 2020. The Company does not expect to record any future charges related to the restructuring plan.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Sep. 30, 2021
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Employee Benefit Plans	Employee Benefit PlansThe Company has a 401(k) savings plan whereby eligible employees may voluntarily contribute a percentage of their compensation. The Company may, at its discretion, match a portion of the employees’ eligible contributions. Contributions by the Company to the plan during the years ended September 30, 2021, 2020, and 2019 were approximately $13.2 million, $11.3 million and $10.5 million, respectively. Contributions made by the Company vest over four years.

Segment Information

Segment Information	12 Months Ended
	Sep. 30, 2021
Segments, Geographical Areas [Abstract]
Segment Reporting Disclosure	Segment Information Operating segments are defined as components of an enterprise for which separate financial information is available and evaluated regularly by the chief operating decision-maker, or decision-making group, in deciding how to allocate resources and in assessing performance. Management has determined that the Company is organized as, and operates in, one reportable operating segment: the development, marketing and sale of application services that optimize the security, performance and availability of network applications, servers and storage systems. Revenues by Geographic Location and Other Information The Company does business in three main geographic regions: the Americas (primarily the United States); Europe, the Middle East, and Africa (EMEA); and the Asia Pacific region (APAC). The Company’s chief operating decision-maker reviews financial information presented on a consolidated basis accompanied by information about revenues by geographic region. The Company’s foreign offices conduct sales, marketing and support activities. Revenues are attributed by geographic location based on the location of the customer. The following presents revenues by geographic region (in thousands): Years Ended September 30, 2021 2020 2019 Americas: United States $ 1,365,625 $ 1,221,190 $ 1,137,556 Other 92,111 95,878 108,112 Total Americas 1,457,736 1,317,068 1,245,668 EMEA 667,219 593,307 553,701 Asia Pacific 478,461 440,447 443,078 $ 2,603,416 $ 2,350,822 $ 2,242,447 The Company generates revenues from the sale of products and services. The Company continues to offer its products through a range of consumption models, from physical systems to software solutions and managed services. The following presents net product revenues by systems and software (in thousands): Years Ended September 30, 2021 2020 2019 Net product revenues Systems revenue $ 748,192 $ 668,313 $ 745,798 Software revenue 498,892 357,543 239,793 Total net product revenue $ 1,247,084 $ 1,025,856 $ 985,591 The following distributors of the Company's products accounted for more than 10% of total net revenue: Years Ended September 30, 2021 2020 2019 Ingram Micro, Inc. 19.2 % 16.7 % 18.2 % Tech Data — — 10.2 % Westcon Group, Inc. — — 10.0 % Synnex Corporation 11.1 % — — The following distributors of the Company's products accounted for more than 10% of total receivables: September 30, 2021 2020 Ingram Micro, Inc. 12.6 % 14.1 % Synnex Corporation 11.9 % 11.4 % Carahsoft Technology 11.5 % — The Company tracks assets by physical location. Long-lived assets consist of property and equipment, net, and are shown below (in thousands): September 30, 2021 2020 United States $ 153,030 $ 190,509 EMEA 20,526 20,361 Other countries 17,608 18,369 $ 191,164 $ 229,239

Subsequent Events

Subsequent Events	12 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Acquisition of Threat Stack, Inc. In September 2021, the Company entered into a Merger Agreement (the “Threat Stack Merger Agreement”) with Threat Stack, Inc. ("Threat Stack"), a provider of cloud security and workload protection solutions. The transaction closed on October 1, 2021 with Threat Stack becoming a wholly-owned subsidiary of F5. The addition of Threat Stack’s cloud security capabilities to F5’s application and API protection solutions is expected to enhance visibility across application infrastructure and workloads to deliver more actionable security insights for customers. Pursuant to the Threat Stack Merger Agreement, at the effective time of the Merger, the capital stock of Threat Stack and the vested outstanding and unexercised stock options in Threat Stack were cancelled and converted to the right to receive approximately $68 million in cash, subject to certain adjustments and conditions set forth in the Threat Stack Merger Agreement. During fiscal 2021, the Company incurred approximately $1.7 million of acquisition and integration related expenses associated with the Threat Stack acquisition, which is included within General and Administrative operating expenses in the Company's Consolidated Income Statements.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policy)	12 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Accounting Principles	Accounting Principles The Company’s consolidated financial statements and accompanying notes are prepared on the accrual basis of accounting in accordance with generally accepted accounting principles in the United States of America (GAAP).
Principles Of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
Use Of Estimates and Assumptions	Use of Estimates and Assumptions The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Examples of estimates and assumptions include: revenue recognition, identifying and evaluating the performance obligations of contracts with non-standard terms, and the allocation of purchase consideration based on the relative fair value standalone sales price of these performance obligations; business combinations, including the determination of fair value for acquired developed technology assets and the evaluation and selection of significant assumptions such as revenue growth rate and technology migration curve; and the incremental borrowing rate for measuring lease obligations. Actual results may differ materially from management's estimates and assumptions due to risks and uncertainties, including uncertainty in the current economic environment due to the global impact of the COVID-19 pandemic.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted CashThe Company considers all highly liquid investments with original maturities of three months or less to be cash equivalents. The Company invests its cash and cash equivalents in deposits with five major financial institutions, which, at times, exceed federally insured limits. The Company has not experienced any losses on its cash and cash equivalents. Amounts included in restricted cash represent those for which the Company's use is restricted by a contractual agreement.
Investments	Investments The Company classifies its investment securities as available-for-sale. Investment securities, consisting of certificates of deposit, corporate and municipal bonds and notes, the United States government and agency securities and international government securities are reported at fair value with the related unrealized gains and losses included as a component of accumulated other comprehensive income (loss) in shareholders’ equity. Realized gains and losses and impairments due to credit losses, in which the fair value of a security is below its amortized cost and management’s intent is to sell the impaired security prior to its recovery, are included in other income (expense). An allowance for credit losses for the excess of amortized cost over the expected cash flows is recorded in other income, net in the Company's consolidated income statements. The cost of investments for purposes of computing realized and unrealized gains and losses is based on the specific identification method. Investments in securities with maturities of less than one year or where management’s intent is to use the investments to fund current operations are classified as short-term investments. Investments with maturities of greater than one year are classified as long-term investments.
Accounts Receivable	Accounts Receivable Trade accounts receivable are recorded at the invoiced amount, net of allowances for credit losses for any potential uncollectible amounts. The allowance for credit losses is based on the assessment of the collectability of accounts. Management regularly reviews the adequacy of the allowance for credit losses on a collective basis by considering the age of each outstanding invoice, each customer’s expected ability to pay and collection history, current market conditions, and reasonable and supportable forecasts of future economic conditions to determine whether the allowance is appropriate. Accounts receivable deemed uncollectible are charged against the allowance for credit losses when identified. For fiscal years ended September 30, 2021 and 2020, the allowance for credit losses activity was not material.
Concentration Of Credit Risk	Concentration of Credit Risk The Company extends credit to customers and is therefore subject to credit risk. The Company performs initial and ongoing credit evaluations of its customers’ financial condition and does not require collateral. An allowance for credit losses is recorded for any potential uncollectible amount. Estimates are used in determining the allowance for credit losses in accordance with the Accounts Receivable policy. See Note 16 - Segment Information, for disaggregated accounts receivable by significant customer. The Company maintains its cash and investment balances with high credit quality financial institutions.
Fair Value Of Financial Instruments	Fair Value of Financial Instruments Short-term and long-term investments are recorded at fair value as the underlying securities are classified as available-for-sale with any unrealized gain or loss being recorded to other comprehensive income. The fair value for securities held is determined using quoted market prices, broker or dealer quotations, or alternative pricing sources with reasonable levels of price transparency.
Inventories	Inventories The Company outsources the manufacturing of its pre-configured hardware platforms to contract manufacturers, who assemble each product to the Company’s specifications. As protection against component shortages and to provide replacement parts for its service teams, the Company also stocks limited supplies of certain key product components. The Company reduces inventory to net realizable value based on excess and obsolete inventories determined primarily by historical usage and forecasted demand. Inventories consist of hardware and related component parts and are recorded at the lower of cost and net realizable value (as determined by the first-in, first-out method).
Property And Equipment	Property and Equipment Property and equipment are stated at net book value. Depreciation of property and equipment are provided using the straight-line method over the estimated useful lives of the assets, ranging from two Property and equipment consist of the following (in thousands): September 30, 2021 2020 Computer equipment $ 166,846 $ 153,256 Software 94,169 95,288 Office furniture and equipment 45,204 45,280 Leasehold improvements 174,504 175,593 480,723 469,417 Accumulated depreciation and amortization (289,559) (240,178) $ 191,164 $ 229,239
Business Combinations	Business Combinations The Company’s business combinations are accounted for under the acquisition method. Management allocates the fair value of purchase consideration to the tangible and intangible assets acquired and liabilities assumed based on their estimated fair values. The excess of the fair value of purchase consideration over the fair values of these identifiable assets and liabilities is recorded as goodwill. Such valuations require management to make significant estimates and assumptions, especially with respect to intangible assets. On January 22, 2021, the Company completed its acquisition of Volterra, Inc. for a total purchase price of $427.2 million, of which approximately $59.5 million of finite-lived developed technology was recorded. Management valued the developed technology using the relief-from-royalty method under the income approach. Management applied significant judgment in estimating the fair value of the acquired developed technology, which involved the use of a significant assumption with respect to the royalty rate.
Goodwill	Goodwill Goodwill represents the excess purchase price over the estimated fair value of net assets acquired as of the acquisition date. The Company tests goodwill for impairment on an annual basis and between annual tests when impairment indicators are identified, and goodwill is written down when impaired. For its annual goodwill impairment test in all periods to date, the Company has operated under one reporting unit and the fair value of its reporting unit has been determined by the Company’s enterprise value. The Company performs its annual goodwill impairment test during the second fiscal quarter. For its annual impairment test performed in the second quarter of fiscal 2021, the Company completed a quantitative assessment and determined that there was no impairment of goodwill. The Company also considered potential impairment indicators of goodwill at September 30, 2021 and noted no indicators of impairment.
Intangible Assets	Intangible AssetsIntangible assets with finite lives consist of acquired developed technology, customer relationships, patents and trademarks, trade names, and non-compete covenants acquired through business combination or asset acquisition. Intangible assets acquired through business combination are recorded at their respective estimated fair values upon acquisition close. Other intangible assets acquired through asset acquisition are recorded at their respective cost. The Company determines the estimated useful lives for acquired intangible assets based on the expected future cash flows associated with the respective asset. The Company's intangible assets with finite lives are amortized using the straight-line method over their estimated useful lives, ranging from two
Software Development Costs	Software Development Costs The authoritative guidance requires certain internal software development costs related to software to be sold to be capitalized upon the establishment of technological feasibility. Capitalized software development costs are amortized over the remaining estimated economic life of the product. The Company's software development costs incurred subsequent to achieving technological feasibility have not been significant and, as a result, all software development costs have been expensed as research and development activities as incurred.
Internal-Use Software	Internal-Use Software The Company capitalizes costs incurred during the application development stage associated with the development of internal-use software systems. The capitalized costs are then amortized over the estimated useful life of the software, which is generally three
Impairment Of Long-Lived Assets	Impairment of Long-Lived AssetsThe Company assesses the impairment of long-lived assets whenever events or changes in business circumstances indicate that the carrying amount of an asset may not be recoverable. When such events occur, management determines whether there has been impairment by comparing the anticipated undiscounted net future cash flows to the related asset’s carrying value. If impairment exists, the asset is written down to its estimated fair value.
Revenue Recognition	Revenue Recognition On October 1, 2018, the Company adopted the new revenue recognition standard by applying the modified retrospective approach to those contracts which were not completed as of October 1, 2018. Results for reporting periods beginning after October 1, 2018 are presented under the new revenue recognition standard, while prior period amounts are not adjusted and continue to be reported under the accounting standards in effect for the prior periods. The Company sells products through distributors, resellers, and directly to end users. Revenue related to the Company's contracts with customers is recognized by following a five-step process: • Identify the contract(s) with a customer. Evidence of a contract generally consists of a purchase order issued pursuant to the terms and conditions of a distributor, reseller or end user agreement. • Identify the performance obligations in the contract. Performance obligations are identified in the Company's contracts and include hardware, hardware-based software, software-only solutions, cloud-based subscription services as well as a broad range of service performance obligations including consulting, training, installation and maintenance. • Determine the transaction price. The purchase price stated in an agreed upon purchase order is generally representative of the transaction price. The Company offers several programs in which customers are eligible for certain levels of rebates if certain conditions are met. When determining the transaction price, the Company considers the effects of any variable consideration. • Allocate the transaction price to the performance obligations in the contract. The transaction price in a contract is allocated based upon the relative standalone selling price of each distinct performance obligation identified in the contract. • Recognize revenue when (or as) the entity satisfies a performance obligation. The Company satisfies performance obligations either over time or at a point in time as discussed in further detail below. Revenue is recognized at the time the related performance obligation is satisfied by transferring control of promised products and services to a customer. Revenue is recognized net of any taxes collected, which are subsequently remitted to governmental authorities. Shipping and handling fees charged to the Company’s 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. The following is a description of the principal activities from which the Company generates revenue: Product Revenue from the sale of the Company's hardware and perpetual software products is generally recognized at a point in time when the product has been fulfilled and the customer is obligated to pay for the product. The Company also offers several products by subscription, either through term-based license agreements or as a service through its cloud-based platform. Revenue for term-based license agreements is recognized at a point in time, when the Company delivers the software license to the customer and the subscription term has commenced. For the Company's software-as-a-service offerings, revenue is recognized ratably as the services are provided. Hardware, including the software run on those devices is considered Systems revenue. Perpetual or subscription software offerings that are deployed on a standalone basis, along with software sold as a service are considered Software revenue. When rights of return are present and the Company cannot estimate returns, revenue is recognized when such rights of return lapse. Payment terms to customers are generally net 30 days to net 60 days. Global Services Revenues for post-contract customer support (PCS) are recognized on a straight-line basis over the service contract term. PCS includes a limited period of telephone support, updates, repair or replacement of any failed product or component that fails during the term of the agreement, bug fixes and rights to upgrades, when and if available. Consulting services are customarily billed at fixed hourly rates, plus out-of-pocket expenses, and revenues are recognized as the consulting is completed. Similarly, training revenue is recognized as the training is completed. Contract Acquisition Costs Sales commissions earned by the Company's sales force are considered incremental and recoverable costs of obtaining a contract with a customer. Sales commissions for initial service contracts and subscription offerings are deferred and then amortized as an expense on a straight-line basis over the period of benefit which management has determined to be 4.5 years and 3 years, respectively. Significant Judgments The Company enters into certain contracts with customers, including flexible consumption programs and multi-year subscriptions, with non-standard terms and conditions. Management exercises significant judgment in assessing contractual terms in these arrangements to identify and evaluate performance obligations. Management allocates consideration to each performance obligation based on relative fair value using standalone selling price and recognizes associated revenue as control is transferred to the customer.
Guarantees And Product Warranties	Guarantees and Product Warranties In the normal course of business to facilitate sales of its products, the Company indemnifies other parties, including customers, resellers, lessors, and parties to other transactions with the Company, with respect to certain matters. The Company has agreed to hold the other party harmless against losses arising from a breach of representations or covenants, or out of intellectual property infringement or other claims made against certain parties. These agreements may limit the time within which an indemnification claim can be made and the amount of the claim. The Company has entered into indemnification agreements with its officers and directors, and the Company’s bylaws contain similar indemnification obligations to the Company’s agents. It is not possible to determine the maximum potential amount under these indemnification agreements due to the limited history of prior indemnification claims and the unique facts and circumstances involved in each particular agreement. The Company offers warranties of one year for hardware for those customers without service contracts, with the option of purchasing additional warranty coverage in yearly increments. The Company accrues for warranty costs as part of its cost of sales based on associated material product costs and technical support labor costs. Warranty expense and accrued warranty costs were not material for all periods presented.
Research And Development	Research and Development Research and development expenses consist of salaries and related benefits of product development personnel, prototype materials and expenses related to the development of new and improved products, and an allocation of facilities, depreciation and amortization expense. Research and development expenses are reflected in the income statements as incurred.
Advertising	Advertising Advertising costs are expensed as incurred. The Company incurred $10.0 million, $7.8 million and $4.7 million in advertising costs during the fiscal years 2021, 2020 and 2019, respectively.
Income Taxes	Income Taxes Deferred income tax assets and liabilities are determined based upon differences between the financial statement and income tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The realization of deferred tax assets is based on historical tax positions and estimates of future taxable income. A valuation allowance is recorded when it is more-likely-than-not that some of the deferred tax assets will not be realized. The Company assesses whether tax benefits claimed or expected to be claimed on a tax return should be recorded in the financial statements. The Company may recognize the tax benefit from an uncertain tax position only if it is more-likely-than-not that the tax position will be sustained on examination by the taxing authorities, including resolution of any related appeals or litigation processes, based on the technical merits of the position. The tax benefits to be recognized in the financial statements from such a position is measured as the largest amount of benefit that has a greater than fifty percent likelihood of being realized upon ultimate settlement. The Company adjusts these liabilities based on a variety of factors, including the evaluation of information not previously available. These adjustments are reflected as increases or decreases to income tax expense in the period in which new information is available. The Company has made an accounting policy election to treat taxes under the global intangible low-taxed income (GILTI) provision as a current period expense.
Foreign Currency	Foreign Currency The functional currency for the Company’s foreign subsidiaries is either the U.S. dollar or the local currency depending on the assessment of management. An entity’s functional currency is determined by the currency of the economic environment in which the majority of cash is generated and expended by the entity. The financial statements of all majority-owned subsidiaries and related entities, with a functional currency other than the U.S. dollar, have been translated into U.S. dollars. All assets and liabilities of the respective entities are translated at year-end exchange rates and all revenues and expenses are translated at average rates during the respective period. Translation adjustments are reported as other comprehensive income (loss) in the consolidated statements of comprehensive income. Foreign currency transaction gains and losses are a result of the effect of exchange rate changes on transactions denominated in currencies other than the functional currency, including U.S. dollars. Gains and losses on those foreign currency transactions are included in determining net income or loss for the period of exchange and are recorded in other income, net. The net effect of foreign currency gains and losses was not material during the fiscal years ended September 30, 2021, 2020 and 2019.
Segments	Segments Management has determined that the Company is organized as, and operates in, one reportable segment and operating segment: the development, marketing and sale of application services that optimize the security, performance and availability of network applications, servers and storage systems.
Stock-Based Compensation	Stock-based Compensation The Company issues incentive awards to its employees through stock-based compensation consisting of restricted stock units (RSUs). RSUs are payable in shares of the Company’s common stock as the periodic vesting requirements are satisfied, generally over one The Company offers an Employee Stock Purchase Plan (ESPP) that permits eligible employees to purchase shares of the Company’s common stock at a discount. In determining the fair value of shares issued under the ESPP, the Company uses the Black-Scholes option pricing model. The assumptions within the option pricing model are based on management’s best estimates at that time, which impact the fair value of the ESPP option calculated under the Black-Scholes methodology and, ultimately, the expense that will be recognized over the life of the ESPP option. The Company has also issued stock options as replacement awards, most notably for those assumed as part of business combinations. The Company used the Black-Scholes option pricing model to determine the fair value of the stock option replacement awards. The assumptions within the option pricing model are based on management’s best estimates at that time, which impact the fair value of the option calculated under the Black-Scholes methodology and, ultimately, the expense that will be recognized over the term of the option. The Company accounts for stock-based compensation using the straight-line attribution method for recognizing compensation expense. The Company recognizes compensation expense for only the portion of stock-based awards that are expected to vest. Therefore, the Company applies estimated forfeiture rates that are derived from historical employee termination behavior. Based on historical differences with forfeitures of stock-based awards granted to the Company’s executive officers and Board of Directors versus grants awarded to all other employees, the Company has developed separate forfeiture expectations for these two groups. The Company issues incentive awards to certain current executive officers as part of its annual equity awards program. A portion of the aggregate number of RSUs issued to executive officers vest in equal quarterly increments, and a portion is subject to the Company achieving specified performance goals. For the performance stock awards granted prior to fiscal 2018, attainment is based on the Company achieving specific quarterly revenue and EBITDA targets. In each case, 70% of the quarterly performance stock grant is based on achieving at least 80% of the quarterly revenue goal set by the Company's Board of Directors, and the other 30% is based on achieving at least 80% of the quarterly EBITDA goal set by the Company's Board of Directors. The quarterly performance stock grant is paid linearly over 80% of the targeted goals. At least 100% of both goals must be attained in order for the quarterly performance stock grant to be awarded over 100%. Each goal is evaluated individually and subject to the 80% achievement threshold and the 100% over-achievement threshold. Each goal is also capped at achievement of 200% above target. In fiscal 2018, the Company's Talent and Compensation Committee adopted a new set of metrics for the performance stock awards that are differentiated from the quarterly revenue and EBITDA measures, including (1) 50% of the annual performance stock grant is based on achieving 80% of the annual revenue goal set by the Company’s Board of Directors; (2) 25% of the annual performance stock grant is based on achieving at least an 18% increase in annual software revenue compared to the prior year; and (3) 25% of the annual performance stock grant is based on relative total shareholder return (TSR) benchmarked to the S&P 500 index. In each case, no vesting or payment with respect to a performance goal shall occur unless a minimum threshold is met for the applicable goal. Vesting and payment with respect to the performance goal is linear above the threshold of the applicable goal and is capped at achievement of 200% above target. The Company recognizes compensation costs for awards with performance conditions and market conditions on a straight-line basis over the requisite service period for each separately vesting portion of the award and, for awards with performance conditions, when it concludes it is probable that the performance condition will be achieved. The Company reassesses the probability of vesting at each balance sheet date and adjusts compensation costs based on the probability assessment.
Comprehensive Income	Comprehensive Income Comprehensive income includes certain changes in equity that are excluded from net income. Specifically, unrealized gains or losses on securities and foreign currency translation adjustments. These changes are included in accumulated other comprehensive income or loss.
Recent Accounting Pronouncements	Recently Adopted Accounting Standards In August 2018, the FASB issued ASU 2018-15, Intangibles - Goodwill and Other - Internal-Use Software (Subtopic 350-40) (ASU 2018-15), which aligns the requirements for capitalizing implementation costs incurred in a hosting arrangement that is a service contract with the requirements for capitalizing implementation costs incurred to develop or obtain internal-use software, and hosting arrangements that include an internal-use software license. The accounting for the service element of a hosting arrangement that is a service contract is not affected by the amendments in this update. The Company adopted this new standard prospectively on October 1, 2020. The adoption of this standard did not have a material impact to the Company’s consolidated financial statements or disclosures. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (ASU 2016-13), which modifies the accounting for credit losses for most financial assets and requires the use of an expected loss model, replacing the currently used incurred loss method. Under this model, entities will be required to estimate the lifetime expected credit loss on such instruments and record an allowance to offset the amortized cost basis of the financial asset, resulting in a net presentation of the amount expected to be collected on the financial asset. The Company adopted this new standard on October 1, 2020 using the modified retrospective approach. The adoption of this standard did not have a material impact on the Company’s condensed consolidated financial statements. Recently Issued Accounting Pronouncements

Accounting Policies (Tables)

Accounting Policies (Tables)	12 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Schedule of Inventories	Inventories consist of the following (in thousands): September 30, 2021 2020 Finished goods $ 13,081 $ 17,096 Raw materials 8,974 10,802 $ 22,055 $ 27,898
Schedule of Earnings Per Share, Basic and Diluted	The following table sets forth the computation of basic and diluted net income per share (in thousands, except per share data): Years Ended September 30, 2021 2020 2019 Numerator Net income $ 331,241 $ 307,441 $ 427,734 Denominator Weighted average shares outstanding — basic 60,707 60,911 60,044 Dilutive effect of common shares from stock options and restricted stock units 1,350 467 412 Weighted average shares outstanding — diluted 62,057 61,378 60,456 Basic net income per share $ 5.46 $ 5.05 $ 7.12 Diluted net income per share $ 5.34 $ 5.01 $ 7.08

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Sep. 30, 2021
Revenue from Contracts with Customers [Abstract]
Capitalized Contract Cost	The table below shows significant movements in capitalized contract acquisition costs (current and noncurrent) for the years ended September 30, 2021, 2020, and 2019 (in thousands): 2021 2020 2019 Balance, beginning of year $ 70,396 $ 59,446 $ — Impacts from adoption of ASC 606 — — 54,608 Additional capitalized contract acquisition costs 41,719 43,557 33,925 Amortization of capitalized contract acquisition costs (34,279) (32,607) (29,087) Balance, end of year $ 77,836 $ 70,396 $ 59,446
Contract with Customer, Asset and Liability	The table below shows significant movements in unbilled receivables (current and noncurrent) for the years ended September 30, 2021, 2020, and 2019 (in thousands): 2021 2020 2019 Balance, beginning of year $ 200,472 $ 132,492 $ — Impacts from adoption of ASC 606 — — 57,499 Revenue recognized during period but not yet billed 60,511 37,260 27,459 Unbilled receivables additions 256,437 129,578 88,068 Unbilled receivables reclassified to accounts receivable (143,138) (98,858) (40,534) Balance, end of year $ 374,282 $ 200,472 $ 132,492 2021 2020 2019 Balance, beginning of year $ 1,272,632 $ 1,198,116 $ 1,015,321 Impacts from adoption of ASC 606 — — 68,078 Amounts added but not recognized as revenues 1,122,081 850,022 866,142 Deferred revenue acquired through acquisition of businesses 779 39,000 — Revenues recognized related to the opening balance of deferred revenue (905,650) (814,506) (751,425) Balance, end of year $ 1,489,842 $ 1,272,632 $ 1,198,116

Business Combinations (Tables)

Business Combinations (Tables)	12 Months Ended
	Sep. 30, 2021
Business Combinations [Abstract]
Schedule of Recognized Identified Assets Acquired and Liabilities Assumed	The allocated purchase consideration to assets acquired and liabilities assumed based on preliminary estimated fair values is presented in the following table (in thousands): Estimated Useful Life Assets acquired Cash, cash equivalents, and restricted cash $ 14,012 Other tangible assets acquired, at fair value 7,499 Identifiable intangible assets: Developed technology 59,500 7 years Customer relationships 500 1 year Goodwill 351,417 Total assets acquired 432,928 Liabilities assumed (5,686) Net assets acquired $ 427,242 The allocated purchase consideration to assets acquired and liabilities assumed is presented in the following table (in thousands): Estimated Useful Life Assets acquired Cash, cash equivalents, and restricted cash $ 53,934 Fair value of tangible assets: Accounts receivable 21,077 Deferred tax assets 29,848 Operating lease right-of-use assets 29,644 Other tangible assets 22,571 Identifiable intangible assets: Developed technology 120,000 7 years Customer relationships 21,000 4 years Trade name 9,500 5 years Goodwill 798,867 Total assets acquired $ 1,106,441 Liabilities assumed Deferred revenue $ (39,000) Operating lease liabilities (30,773) Other assumed liabilities (18,571) Total liabilities assumed $ (88,344) Net assets acquired $ 1,018,097 The allocated purchase consideration to assets acquired and liabilities assumed is presented in the following table (in thousands): Estimated Useful Life Assets acquired Cash and cash equivalents $ 29,911 Fair value of tangible assets: Other tangible assets 23,699 Identifiable intangible assets: Developed technology 62,500 7 years Customer relationships 12,000 15 years Trade name 14,500 7 years Non-competition agreements 300 2 years Goodwill 510,328 Total assets acquired $ 653,238 Liabilities assumed Other assumed liabilities $ (9,116) Total liabilities assumed $ (9,116) Net assets acquired $ 644,122

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Schedule Of Financial Assets Measured At Fair Value on A Recurring Basis	The Company’s financial assets measured at fair value on a recurring basis subject to the disclosure requirements at September 30, 2021, were as follows (in thousands): Fair Value Measurements at Reporting Date Using Fair Value at Quoted Prices in Significant Significant Cash equivalents $ 17,150 $ 4,397 $ — $ 21,547 Short-term investments Available-for-sale securities — certificates of deposit — 255 — 255 Available-for-sale securities — corporate bonds and notes — 186,107 — 186,107 Available-for-sale securities — municipal bonds and notes — 13,566 — 13,566 Available-for-sale securities — U.S. government securities — 102,615 — 102,615 Available-for-sale securities — U.S. government agency securities — 27,087 — 27,087 Long-term investments Available-for-sale securities — corporate bonds and notes — 53,107 — 53,107 Available-for-sale securities — municipal bonds and notes — 11,111 — 11,111 Available-for-sale securities — U.S. government securities — 59,608 — 59,608 Available-for-sale securities — U.S. government agency securities — 8,952 — 8,952 Total $ 17,150 $ 466,805 $ — $ 483,955 The Company’s financial assets measured at fair value on a recurring basis subject to the disclosure requirements at September 30, 2020, were as follows (in thousands): Fair Value Measurements at Reporting Date Using Fair Value at Quoted Prices in Significant Significant Cash equivalents $ 43,553 $ 207,417 $ — $ 250,970 Short-term investments Available-for-sale securities — corporate bonds and notes — 189,662 — 189,662 Available-for-sale securities — municipal bonds and notes — 6,146 — 6,146 Available-for-sale securities — U.S. government securities — 117,374 — 117,374 Available-for-sale securities — U.S. government agency securities — 47,151 — 47,151 Long-term investments Available-for-sale securities — corporate bonds and notes — 102,939 — 102,939 Total $ 43,553 $ 670,689 $ — $ 714,242
Impairment Charges	Impairment charges were allocated to the following income statement line items for the years ended September 30, 2021, 2020, and 2019 (in thousands): Years Ended September 30, 2021 2020 2019 Cost of net product revenue $ 2,865 $ 241 $ — Cost of net service revenue 3,492 1,034 — Sales and marketing 11,515 2,876 — Research and development 12,974 2,906 — General and administrative 9,852 2,616 6,273 Total impairment charges $ 40,698 $ 9,673 $ 6,273

Short-Term And Long-Term Inve_2

Short-Term And Long-Term Investments (Tables)	12 Months Ended
	Sep. 30, 2021
Investments, Debt and Equity Securities [Abstract]
Schedule Of Short-Term And Long-Term Investments	Short-term investments consist of the following (in thousands): September 30, 2021 Cost or Gross Gross Fair Value Certificates of deposit $ 255 $ — $ — $ 255 Corporate bonds and notes 186,043 116 (52) 186,107 Municipal bonds and notes 13,570 1 (5) 13,566 U.S. government securities 102,607 12 (4) 102,615 U.S. government agency securities 27,096 — (9) 27,087 $ 329,571 $ 129 $ (70) $ 329,630 September 30, 2020 Cost or Gross Gross Fair Value Corporate bonds and notes $ 188,932 $ 736 $ (6) $ 189,662 Municipal bonds and notes 6,143 3 — 6,146 U.S. government securities 117,363 14 (3) 117,374 U.S. government agency securities 47,148 3 — 47,151 $ 359,586 $ 756 $ (9) $ 360,333 Long-term investments consist of the following (in thousands): September 30, 2021 Cost or Gross Gross Fair Value Corporate bonds and notes $ 53,128 $ 13 $ (34) $ 53,107 Municipal bonds and notes 11,114 1 (4) 11,111 U.S. government securities 59,614 2 (8) 59,608 U.S. government agency securities 8,957 — (5) 8,952 $ 132,813 $ 16 $ (51) $ 132,778 September 30, 2020 Cost or Gross Gross Fair Value Corporate bonds and notes $ 102,206 $ 756 $ (23) $ 102,939 $ 102,206 $ 756 $ (23) $ 102,939
Schedule Of Investments That Have Been In A Continuous Unrealized Loss Position	The following table summarizes investments that have been in a continuous unrealized loss position for less than 12 months and those that have been in a continuous unrealized loss position for more than 12 months as of September 30, 2021 (in thousands): Less Than 12 Months 12 Months or Greater Total September 30, 2021 Fair Value Gross Fair Gross Fair Value Gross Corporate bonds and notes $ 151,986 $ (86) $ — $ — $ 151,986 $ (86) Municipal bonds and notes 13,764 (9) — — 13,764 (9) U.S. government securities 77,401 (12) — — 77,401 (12) U.S. government agency securities 31,384 (14) — — 31,384 (14) Total $ 274,535 $ (121) $ — $ — $ 274,535 $ (121) The following table summarizes investments that have been in a continuous unrealized loss position for less than 12 months and those that have been in a continuous unrealized loss position for more than 12 months as of September 30, 2020 (in thousands): Less Than 12 Months 12 Months or Greater Total September 30, 2020 Fair Value Gross Fair Value Gross Fair Value Gross Corporate bonds and notes $ 43,492 $ (28) $ 5,006 $ (1) $ 48,498 $ (29) U.S. government securities 41,812 (3) — — 41,812 (3) Total $ 85,304 $ (31) $ 5,006 $ (1) $ 90,310 $ (32)

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	12 Months Ended
	Sep. 30, 2021
Balance Sheet Details [Abstract]
Cash, Cash Equivalents and Restricted Cash	The following table provides a reconciliation of the Company’s cash and cash equivalents and restricted cash reported within the consolidated balance sheets that sum to the total cash, cash equivalents and restricted cash shown in the Company’s consolidated statements of cash flows for the periods presented (in thousands): September 30, 2021 2020 Cash and cash equivalents $ 580,977 $ 849,556 Restricted cash included in other assets, net 3,356 3,270 Total cash, cash equivalents and restricted cash $ 584,333 $ 852,826
Inventories	Inventories consist of the following (in thousands): September 30, 2021 2020 Finished goods $ 13,081 $ 17,096 Raw materials 8,974 10,802 $ 22,055 $ 27,898
Other Current Assets	Other current assets consist of the following (in thousands): September 30, 2021 2020 Unbilled receivables $ 215,396 $ 138,096 Prepaid expenses 59,636 47,197 Capitalized contract acquisition costs 34,265 29,650 Other 28,605 44,563 $ 337,902 $ 259,506
Property, Plant and Equipment	Property and Equipment Property and equipment are stated at net book value. Depreciation of property and equipment are provided using the straight-line method over the estimated useful lives of the assets, ranging from two Property and equipment consist of the following (in thousands): September 30, 2021 2020 Computer equipment $ 166,846 $ 153,256 Software 94,169 95,288 Office furniture and equipment 45,204 45,280 Leasehold improvements 174,504 175,593 480,723 469,417 Accumulated depreciation and amortization (289,559) (240,178) $ 191,164 $ 229,239
Goodwill	Changes in the carrying amount of goodwill during fiscal years 2021 and 2020 are summarized as follows (in thousands): Balance, September 30, 2019 $ 1,065,379 Acquisition of Shape Security, Inc. 799,611 Other (6,024) Balance, September 30, 2020 1,858,966 Acquisition of Volterra, Inc. 351,417 Other 6,170 Balance, September 30, 2021 $ 2,216,553
Other Assets	Other assets consist of the following (in thousands): September 30, 2021 2020 Intangible assets $ 237,178 $ 225,900 Unbilled receivables 158,885 62,377 Capitalized contract acquisition costs 43,571 40,746 Other 32,924 18,424 $ 472,558 $ 347,447
Intangible Assets	Intangible assets are included in other assets on the balance sheet and consist of the following (in thousands): September 30, 2021 September 30, 2020 Gross Accumulated Net Carrying Gross Accumulated Net Carrying Developed technology $ 305,673 $ (111,279) $ 194,394 $ 246,173 $ (76,556) $ 169,617 Customer relationships 41,742 (17,865) 23,877 41,242 (10,657) 30,585 Patents and trademarks 20,260 (17,180) 3,080 20,260 (14,448) 5,812 Trade names 24,973 (9,146) 15,827 24,973 (5,174) 19,799 Non-compete covenants 2,260 (2,260) — 2,260 (2,173) 87 $ 394,908 $ (157,730) $ 237,178 $ 334,908 $ (109,008) $ 225,900
Estimated Amortization Expense For Intangible Assets	For intangible assets held as of September 30, 2021, amortization expense for the five succeeding fiscal years is as follows (in thousands): 2022 $ 50,095 2023 49,125 2024 43,860 2025 38,124 2026 32,860 $ 214,064
Accrued Liabilities	Accrued liabilities consist of the following (in thousands): September 30, 2021 2020 Payroll and benefits $ 179,147 $ 169,708 Operating lease liabilities, current 49,286 46,010 Income and other tax accruals 44,075 33,048 Other 68,979 72,632 $ 341,487 $ 321,398
Other Long-term Liabilities	Other long-term liabilities consist of the following (in thousands): September 30, 2021 2020 Income taxes payable $ 66,081 $ 49,846 Other 9,155 9,665 $ 75,236 $ 59,511

Debt Facilities (Tables)

Debt Facilities (Tables)	12 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Schedule of Maturities of Long-term Debt	The following table presents the scheduled principal maturities as of September 30, 2021 (in thousands): Fiscal Years Ending September 30: 2022 $ 20,000 2023 350,000 Total $ 370,000

Leases (Tables)

Leases (Tables)	12 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Lease, Cost	The components of the Company's operating lease expenses for the years ended September 30, 2021 and 2020 were as follows (in thousands): Fiscal year ended September 30, 2021 2020 Operating lease expense $ 47,993 $ 49,925 Short-term lease expense 2,953 3,563 Variable lease expense 25,200 21,980 Total lease expense $ 76,146 $ 75,468
Assets And Liabilities Lessee	Supplemental balance sheet information related to the Company's operating leases was as follows (in thousands, except lease term and discount rate): September 30, 2021 2020 Operating lease right-of-use assets, net $ 244,934 $ 300,680 Operating lease liabilities, current 1 49,286 46,010 Operating lease liabilities, long-term 296,945 338,715 Total operating lease liabilities $ 346,231 $ 384,725 Weighted average remaining lease term (in years) 9.7 10.2 Weighted average discount rate 2.60 % 2.58 % (1) Current portion of operating lease liabilities is included in accrued liabilities on the Company's consolidated balance sheets.
Lessee, Operating Lease, Liability, Maturity	As of September 30, 2021, the future operating leases payments for each of the next five years and thereafter is as follows (in thousands): Fiscal Years Ending September 30: Operating Lease 2022 $ 57,849 2023 48,458 2024 41,142 2025 33,600 2026 26,609 Thereafter 191,142 Total lease payments 398,800 Less: imputed interest (52,569) Total lease liabilities $ 346,231
Future Minimum Rental Payments for Operating Leases	Prior to the adoption of the Leasing Standard, future minimum operating lease payments, net of sublease income, were as follows as of September 30, 2019 (in thousands): Fiscal Year Gross Lease Sublease Net Lease 2020 $ 54,046 $ 683 $ 53,363 2021 50,712 1,051 49,661 2022 47,550 1,082 46,468 2023 36,514 368 36,146 2024 33,971 — 33,971 Thereafter 242,826 — 242,826 $ 465,619 $ 3,184 $ 462,435

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Components Of Income Before Income Taxes	The United States and international components of income before income taxes are as follows (in thousands): Years Ended September 30, 2021 2020 2019 United States $ 189,398 $ 216,409 $ 360,648 International 197,539 179,988 180,463 $ 386,937 $ 396,397 $ 541,111
Schedule Of Provision For Income Taxes (Benefit)	The provision for income taxes consists of the following (in thousands): Years Ended September 30, 2021 2020 2019 Current U.S. federal $ 53,107 $ 26,978 $ 43,039 State 16,686 4,230 13,864 Foreign 62,832 50,368 49,197 Total 132,625 81,576 106,100 Deferred U.S. federal (61,739) 10,875 8,716 State (15,294) (1,121) 1,617 Foreign 104 (2,374) (3,056) Total (76,929) 7,380 7,277 $ 55,696 $ 88,956 $ 113,377
Schedule Of Effective Tax Rate Differs From The U.S. Federal Statutory Rate	The effective tax rate differs from the U.S. federal statutory rate as follows (in thousands): Years Ended September 30, 2021 2020 2019 Income tax provision at statutory rate $ 81,257 $ 83,243 $ 113,633 State taxes, net of federal benefit 5,118 4,258 14,206 Tax impact of foreign operations (26,881) (7,693) (9,161) Research and development and other credits (18,055) (11,843) (12,760) Stock-based and other compensation 12,740 18,002 6,771 Other 1,517 2,989 688 $ 55,696 $ 88,956 $ 113,377
Schedule Of Tax Effects To Deferred Tax Assets And Liabilities	The tax effects of the temporary differences that give rise to the deferred tax assets and liabilities are as follows (in thousands): Years Ended September 30, 2021 2020 Deferred tax assets Net operating loss carry-forwards $ 41,252 $ 54,842 Capitalized research and development costs 95,259 — Accrued compensation and benefits 13,207 13,162 Stock-based compensation 12,829 13,010 Deferred revenue 30,115 40,577 Lease liabilities 23,747 19,656 Other accruals and reserves 18,450 17,384 Tax credit carryforwards 34,187 15,807 Depreciation 580 620 269,626 175,058 Valuation allowance (40,404) (32,587) 229,222 142,471 Deferred tax liabilities Purchased intangibles (57,219) (46,491) Depreciation (26,516) (34,757) Deferred costs (13,057) (11,924) Other accruals and reserves (6,651) (4,728) (103,443) (97,900) Net deferred tax assets $ 125,779 $ 44,571
Schedule Of Reconciliation Of Beginning And Ending Amount Of Unrecognized Tax Benefits	The following table provides a reconciliation of the beginning and ending amount of unrecognized tax benefits in fiscal years 2021, 2020 and 2019 (in thousands): 2021 2020 2019 Balance, beginning of period $ 51,767 $ 42,287 $ 31,672 Gross increases related to prior period tax positions 14,867 8,664 5,129 Gross decreases related to prior period tax positions — (1,051) (287) Gross increases related to current period tax positions 12,595 9,272 7,756 Decreases relating to settlements with tax authorities (321) (3,578) — Reductions due to lapses of statute of limitations (8,094) (3,827) (1,983) Balance, end of period $ 70,814 $ 51,767 $ 42,287

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement, Noncash Expense [Abstract]
Schedule Of Assumptions In Determining The Fair Value Of Shares Issued Under The Employee Stock Purchase Plan	In determining the fair value of the right to purchase under the Employee Stock Purchase Plan, the Company uses the Black-Scholes option pricing model that employs the following key assumptions: Employee Stock Purchase Plan 2021 2020 2019 Risk-free interest rate 0.07% - 0.13% 1.10% - 1.97% 2.25% - 2.51% Expected dividend — — — Expected term 0.5 years 0.5 years 0.5 years Expected volatility 29.67% - 37.22% 26.32% - 41.94% 18.14% - 31.74%
Schedule Of Summary Of Restricted Stock Unit Activity	A summary of restricted stock unit activity under the 2014 Plan is as follows: Performance Stock Units Restricted Stock Units Outstanding Weighted Outstanding Weighted Balance, September 30, 2020 145,869 $ 146.42 1,204,290 $ 146.39 Units granted 153,434 117.16 1,510,829 137.33 Units vested (59,365) 137.13 (1,183,086) 183.01 Units cancelled (9,012) 162.72 (191,485) 138.09 Balance, September 30, 2021 230,926 $ 136.47 1,340,548 $ 141.90
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions	In determining the fair value of the portion of the performance awards based on Total Shareholder Return, the Company uses a Monte Carlo simulation model that employs the following key assumptions: Expected Volatility Fair Value Expected Term Risk-Free Index Expected Grant Date per Share (in years) Interest Rate F5 Members Dividend November 2, 2020 Tranche 1 $ 182.01 0.91 0.13 % 41.89 % 53.54 % — Tranche 2 $ 185.86 1.91 0.16 % 34.77 % 41.85 % — Tranche 3 $ 189.57 2.91 0.20 % 31.74 % 37.45 % —
Schedule of Nonvested Restricted Stock Units Activity	As of September 30, 2021, the following annual equity grants for executive officers or a portion thereof are outstanding: Grant Date RSUs Granted Vesting Schedule Vesting Period Date Fully Vested November 2, 2020 257,568 Quarterly, Annually 1 3 years November 1, 2023 November 1, 2019 228,616 Quarterly, Annually 1 3 years November 1, 2022 November 1, 2018 144,066 Quarterly, Annually 1 3 years November 1, 2021 November 1, 2017 140,135 Quarterly, Annually 1 4 years November 1, 2021 (1) 50% of the annual equity grant vests in equal quarterly increments and 50% is subject to the Company achieving specified annual performance goals.
Schedule Of Stock Option Activity	A summary of stock option activity under all of the Company’s plans is as follows: Options Outstanding Number of Weighted Balance, September 30, 2020 391,100 $ 36.71 Options granted 145,360 14.84 Options exercised (163,880) 29.68 Options cancelled (47,956) 34.21 Balance, September 30, 2021 324,624 $ 30.83
Schedule Of Outstanding Stock Options Currently Exercisable, Vested And Expected To Vest	A summary of options outstanding that are exercisable and that have vested and are expected to vest as of September 30, 2021 is as follows: Number of Weighted Weighted Aggregate (In thousands) Stock options outstanding 324,624 7.19 $ 30.83 $ 54,520 Exercisable 158,544 6.67 $ 28.15 $ 27,052 Vested and expected to vest 313,777 7.16 $ 30.53 $ 52,794 (1) Aggregate intrinsic value represents the difference between the fair value of the Company’s common stock underlying these options at September 30, 2021 and the related exercise prices.
Schedule Of Equity Based Awards (Including Stock Options And Restricted Stock Units)	As of September 30, 2021, equity based awards (including stock options and restricted stock units) are available for future issuance as follows: Awards Balance, September 30, 2020 2,714,958 Granted (1,976,525) Cancelled 299,248 Additional shares reserved (terminated), net 950,729 Balance, September 30, 2021 1,988,410

Net Income Per Share (Tables)

Net Income Per Share (Tables)	12 Months Ended
	Sep. 30, 2021
Net Income Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	The following table sets forth the computation of basic and diluted net income per share (in thousands, except per share data): Years Ended September 30, 2021 2020 2019 Numerator Net income $ 331,241 $ 307,441 $ 427,734 Denominator Weighted average shares outstanding — basic 60,707 60,911 60,044 Dilutive effect of common shares from stock options and restricted stock units 1,350 467 412 Weighted average shares outstanding — diluted 62,057 61,378 60,456 Basic net income per share $ 5.46 $ 5.05 $ 7.12 Diluted net income per share $ 5.34 $ 5.01 $ 7.08

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Sep. 30, 2021
Segments, Geographical Areas [Abstract]
Schedule Of Revenues By Geographic Region	The following presents revenues by geographic region (in thousands): Years Ended September 30, 2021 2020 2019 Americas: United States $ 1,365,625 $ 1,221,190 $ 1,137,556 Other 92,111 95,878 108,112 Total Americas 1,457,736 1,317,068 1,245,668 EMEA 667,219 593,307 553,701 Asia Pacific 478,461 440,447 443,078 $ 2,603,416 $ 2,350,822 $ 2,242,447
Schedule of Revenues by Systems and Software	The following presents net product revenues by systems and software (in thousands): Years Ended September 30, 2021 2020 2019 Net product revenues Systems revenue $ 748,192 $ 668,313 $ 745,798 Software revenue 498,892 357,543 239,793 Total net product revenue $ 1,247,084 $ 1,025,856 $ 985,591
Schedule of Revenue by Major Customers by Reporting Segments	The following distributors of the Company's products accounted for more than 10% of total net revenue: Years Ended September 30, 2021 2020 2019 Ingram Micro, Inc. 19.2 % 16.7 % 18.2 % Tech Data — — 10.2 % Westcon Group, Inc. — — 10.0 % Synnex Corporation 11.1 % — —
Schedule of Receivables by Major Customers by Reporting Segments	The following distributors of the Company's products accounted for more than 10% of total receivables: September 30, 2021 2020 Ingram Micro, Inc. 12.6 % 14.1 % Synnex Corporation 11.9 % 11.4 % Carahsoft Technology 11.5 % —
Long-lived Assets by Geographic Areas [Table Text Block]	The Company tracks assets by physical location. Long-lived assets consist of property and equipment, net, and are shown below (in thousands): September 30, 2021 2020 United States $ 153,030 $ 190,509 EMEA 20,526 20,361 Other countries 17,608 18,369 $ 191,164 $ 229,239

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies - Narrative (Details)	Jan. 22, 2021USD ($)	Sep. 30, 2021USD ($)segment	Sep. 30, 2020USD ($)segment	Sep. 30, 2019USD ($)segment
Segment Reporting [Abstract]
Number of Reportable Segments | segment		1	1	1
Advertising
Advertising Expense		$ 10,000,000	$ 7,800,000	$ 4,700,000
Restricted Stock Units (RSUs) [Member]
Restricted Stock Award
Award vesting period		2 years	2 years	2 years
Restricted Stock Units (RSUs) [Member] | Annual Equity Program [Member]
Restricted Stock Award
Percentage Of Quarterly Performance Stock Grant Based On Achieving Quarterly Revenue Goal		70.00%
Percentage Of Quarterly Revenue Goal To Be Achieved For Performance Stock Grant		80.00%
Percentage Of Quarterly Performance Stock Grant Based On Achieving Ebitda Goal		30.00%
Percentage Of Quarterly Ebitda Goal To Be Achieved For Performance Stock Grant		80.00%
Threshold percentage of targeted goals above which quarterly performance stock grant is paid linearly		80.00%
Percentage Of Over-Achievement Threshold To Which The Goals Are Entitled		100.00%
Percentage Of Over-Achievement To Which Quarterly Performance Based Vesting Cannot Exceed		200.00%
Percentage Of Annual Performance Stock Grant Based On Achieving Annual Revenue Goal		50.00%
Percentage Of Annual Revenue Goal To Be Achieved For Performance Stock Grant		80.00%
Percentage Of Annual Performance Stock Grant Based On Achieving Annual Increase in Stand-alone Software Goal		25.00%
Percentage Of Annual Increase in Stand-alone Software Goal To Be Achieved For Performance Stock Grant		18.00%
Percentage Of Annual Performance Stock Grant Based On Achieving Relative Total Shareholder Return Benchmarked to the S&P 500 Index Goal		25.00%
Percentage Of Over-Achievement To Which Annual Performance Based Vesting Cannot Exceed		200.00%
Maintenance [Member]
Revenue Recognition
Capitalized Contract Cost, Amortization Period		4 years 6 months
Subscription and Circulation [Member]
Revenue Recognition
Capitalized Contract Cost, Amortization Period		3 years
Hardware [Member]
Guarantees and Product Warranties
Standard Product Warranty Period		1 year
Volterra, Inc.
Business Combinations
Total Purchase Price	$ 427,200,000
Volterra, Inc. | Developed Technology Rights
Business Combinations
Identifiable intangible assets:	$ 59,500,000
Minimum
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life		2 years
Property, Plant and Equipment [Abstract]
Property and equipment, useful life		2 years
Revenue Recognition
Accounts Receivable Payment Term Period In Days		30 days
Restricted Stock Award
Award vesting period		1 year
Minimum | Software and Software Development Costs [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life		3 years
Maximum
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life		15 years
Property, Plant and Equipment [Abstract]
Property and equipment, useful life		5 years
Revenue Recognition
Accounts Receivable Payment Term Period In Days		60 days
Restricted Stock Award
Award vesting period		4 years
Maximum | Software and Software Development Costs [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Finite-Lived Intangible Asset, Useful Life		5 years

Summary Of Significant Accoun_4

Summary Of Significant Accounting Policies - Schedule Of Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Accounting Policies [Abstract]
Finished goods	$ 13,081	$ 17,096
Raw materials	8,974	10,802
Inventories, Total	$ 22,055	$ 27,898

Summary Of Significant Accoun_5

Summary Of Significant Accounting Policies - Property And Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Property, Plant and Equipment [Line Items]
Computer equipment	$ 166,846	$ 153,256
Capitalized Computer Software, Gross	94,169	95,288
Office furniture and equipment	45,204	45,280
Leasehold improvements	174,504	175,593
Property and equipment, gross	480,723	469,417
Accumulated depreciation and amortization	(289,559)	(240,178)
Property, Plant and Equipment, Net	$ 191,164	$ 229,239
Minimum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Maximum
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years

Summary Of Significant Accoun_6

Summary Of Significant Accounting Policies - Schedule Of Computation Of Basic And Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Accounting Policies [Abstract]
Net income	$ 331,241	$ 307,441	$ 427,734
Weighted average shares outstanding - basic	60,707	60,911	60,044
Dilutive effect of common shares from stock options and restricted stock units	1,350	467	412
Weighted average shares outstanding - diluted	62,057	61,378	60,456
Basic net income per share (USD per share)	$ 5.46	$ 5.05	$ 7.12
Diluted net income per share (USD per share)	$ 5.34	$ 5.01	$ 7.08

Revenue from Contracts with C_3

Revenue from Contracts with Customers - Capitalized Contract Acquisition Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Capitalized Contract Acquisition Costs [Abstract]
Balance, beginning of year	$ 70,396	$ 59,446	$ 0
Capitalized Contract Cost, Cumulative Catch-up Adjustment to Revenue, Change in Estimate of Transaction Price	0	0	54,608
Capitalized Contract Cost, Deferred Acquisition Costs	41,719	43,557	33,925
Capitalized Contract Cost, Amortization	(34,279)	(32,607)	(29,087)
Balance, end of year	$ 77,836	$ 70,396	$ 59,446

Revenue from Contracts with C_4

Revenue from Contracts with Customers - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Change in Contract with Customer, Asset [Roll Forward]
Balance, beginning of year	$ 200,472	$ 132,492	$ 0
Impacts from adoption of ASC 606	0	0	57,499
Revenue recognized during period but not yet billed	60,511	37,260	27,459
Unbilled receivables additions	256,437	129,578	88,068
Unbilled receivables reclassified to accounts receivable	(143,138)	(98,858)	(40,534)
Balance, end of year	374,282	200,472	132,492
Change in Contract with Customer, Liability [Roll Forward]
Balance, beginning of year	1,272,632	1,198,116	1,015,321
Impacts from adoption of ASC 606	0	0	68,078
Amounts added but not recognized as revenues	1,122,081	850,022	866,142
Deferred revenue acquired through acquisition of businesses	779	39,000	0
Revenues recognized related to the opening balance of deferred revenue	(905,650)	(814,506)	(751,425)
Balance, end of year	$ 1,489,842	$ 1,272,632	$ 1,198,116

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Narrative (Details) - USD ($)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Capitalized Contract Cost, Amortization	$ 34,279,000	$ 32,607,000	$ 29,087,000
Capitalized Contract Cost, Impairment Loss	$ 0	$ 0	$ 0

Revenue from Contracts with C_6

Revenue from Contracts with Customers - Remaining Performance Obligations. (Details) $ in Billions	Sep. 30, 2021USD ($)
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 1.5
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Percentage	65.00%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-10-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Percentage	21.30%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	12 months

Business Combinations - Purchas

Business Combinations - Purchase Price Allocation (Details) - USD ($)	Jan. 22, 2021	Jan. 24, 2020	May 08, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Fair Value of intangible Assets Abstract [Abstract]
Goodwill				$ 2,216,553,000	$ 1,858,966,000	$ 1,065,379,000
Shape Security, Inc.
AssetsAcquiredAbstract [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents		$ 53,934,000
Fair Value of intangible Assets Abstract [Abstract]
Accounts receivable		21,077,000
Deferred tax assets		29,848,000
Operating lease right-of-use assets		29,644,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other		$ 22,571,000
Identifiable Intangible Assets Useful Life		6 years 6 months
Goodwill		$ 798,867,000
Total assets acquired		1,106,441,000
Liabilities assumed
Deferred revenue		(39,000,000)
Operating lease liabilities		(30,773,000)
Other assumed liabilities		(18,571,000)
Total liabilities assumed		(88,344,000)
Net assets acquired		1,018,097,000
Shape Security, Inc. | Developed Technology Rights
Fair Value of intangible Assets Abstract [Abstract]
Identifiable intangible assets:		$ 120,000,000
Identifiable Intangible Assets Useful Life		7 years
Shape Security, Inc. | Customer Relationships
Fair Value of intangible Assets Abstract [Abstract]
Identifiable intangible assets:		$ 21,000,000
Identifiable Intangible Assets Useful Life		4 years
Shape Security, Inc. | Trade Names
Fair Value of intangible Assets Abstract [Abstract]
Identifiable intangible assets:		$ 9,500,000
Identifiable Intangible Assets Useful Life		5 years
Volterra, Inc.
AssetsAcquiredAbstract [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	$ 14,012,000
Fair Value of intangible Assets Abstract [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets	$ 7,499,000
Identifiable Intangible Assets Useful Life	6 years 11 months 12 days
Goodwill	$ 351,417,000
Total assets acquired	432,928,000
Liabilities assumed
Total liabilities assumed	(5,686,000)
Net assets acquired	427,242,000
Volterra, Inc. | Developed Technology Rights
Fair Value of intangible Assets Abstract [Abstract]
Identifiable intangible assets:	$ 59,500,000
Identifiable Intangible Assets Useful Life	7 years
Volterra, Inc. | Customer Relationships
Fair Value of intangible Assets Abstract [Abstract]
Identifiable intangible assets:	$ 500,000
Identifiable Intangible Assets Useful Life	1 year
F5 Networks Acquisition of Nginx
AssetsAcquiredAbstract [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents			$ 29,911,000
Fair Value of intangible Assets Abstract [Abstract]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other			$ 23,699,000
Identifiable Intangible Assets Useful Life			8 years 1 month 6 days
Goodwill			$ 510,328,000
Total assets acquired			653,238,000
Liabilities assumed
Other assumed liabilities			(9,116,000)
Total liabilities assumed			(9,116,000)
Net assets acquired			644,122,000
F5 Networks Acquisition of Nginx | Developed Technology Rights
Fair Value of intangible Assets Abstract [Abstract]
Identifiable intangible assets:			$ 62,500,000
Identifiable Intangible Assets Useful Life			7 years
F5 Networks Acquisition of Nginx | Customer Relationships
Fair Value of intangible Assets Abstract [Abstract]
Identifiable intangible assets:			$ 12,000,000
Identifiable Intangible Assets Useful Life			15 years
F5 Networks Acquisition of Nginx | Trade Names
Fair Value of intangible Assets Abstract [Abstract]
Identifiable intangible assets:			$ 14,500,000
Identifiable Intangible Assets Useful Life			7 years
F5 Networks Acquisition of Nginx | Non-competition Agreements
Fair Value of intangible Assets Abstract [Abstract]
Identifiable intangible assets:			$ 300,000
Identifiable Intangible Assets Useful Life			2 years

Business Combinations - Narrati

Business Combinations - Narrative (Details) - USD ($) $ in Thousands	Jan. 22, 2021	Jan. 24, 2020	May 08, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Business Acquisition [Line Items]
Goodwill, Other Increase (Decrease)				$ 6,170	$ (6,024)
Volterra, Inc.
Business Acquisition [Line Items]
Total Purchase Price	$ 427,200
Identifiable Intangible Assets Useful Life	6 years 11 months 12 days
Volterra, Inc. | General and Administrative Expense
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs				9,500
Shape Security, Inc.
Business Acquisition [Line Items]
Total Purchase Price		$ 1,000,000
Transaction Costs		$ 23,200
Identifiable Intangible Assets Useful Life		6 years 6 months
Goodwill, Other Increase (Decrease)				$ (700)
Shape Security, Inc. | General and Administrative Expense
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs					$ 15,300
F5 Networks Acquisition of Nginx
Business Acquisition [Line Items]
Total Purchase Price			$ 643,200
Transaction Costs			$ 19,000
Identifiable Intangible Assets Useful Life			8 years 1 month 6 days
Tax Deductible Goodwill			$ 500,500
F5 Networks Acquisition of Nginx | General and Administrative Expense
Business Acquisition [Line Items]
Business Combination, Acquisition Related Costs						$ 1,000
Developed Technology Rights | Volterra, Inc.
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life	7 years
Developed Technology Rights | Shape Security, Inc.
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life		7 years
Developed Technology Rights | F5 Networks Acquisition of Nginx
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life			7 years
Customer Relationships | Volterra, Inc.
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life	1 year
Customer Relationships | Shape Security, Inc.
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life		4 years
Customer Relationships | F5 Networks Acquisition of Nginx
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life			15 years
Trade Names | Shape Security, Inc.
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life		5 years
Trade Names | F5 Networks Acquisition of Nginx
Business Acquisition [Line Items]
Identifiable Intangible Assets Useful Life			7 years

Fair Value Measurements - Sched

Fair Value Measurements - Schedule Of Financial Assets Measured At Fair Value On A Recurring Basis (Details) - Fair Value, Recurring [Member] - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value	$ 21,547	$ 250,970
Fair Value	483,955	714,242
Quoted Prices In Active Markets For Identical Securities (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value	17,150	43,553
Fair Value	17,150	43,553
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value	4,397	207,417
Fair Value	466,805	670,689
Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value	0	0
Fair Value	0	0
Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	255
Certificates of Deposit [Member] | Quoted Prices In Active Markets For Identical Securities (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	0
Certificates of Deposit [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	255
Certificates of Deposit [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	0
Corporate Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	186,107	189,662
Debt Securities, Available-for-sale, Noncurrent	53,107	102,939
Corporate Bonds And Notes [Member] | Quoted Prices In Active Markets For Identical Securities (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	0	0
Debt Securities, Available-for-sale, Noncurrent	0	0
Corporate Bonds And Notes [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	186,107	189,662
Debt Securities, Available-for-sale, Noncurrent	53,107	102,939
Corporate Bonds And Notes [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	0	0
Debt Securities, Available-for-sale, Noncurrent	0	0
Municipal Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	13,566	6,146
Debt Securities, Available-for-sale, Noncurrent	11,111
Municipal Bonds And Notes [Member] | Quoted Prices In Active Markets For Identical Securities (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	0	0
Debt Securities, Available-for-sale, Noncurrent	0
Municipal Bonds And Notes [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	13,566	6,146
Debt Securities, Available-for-sale, Noncurrent	11,111
Municipal Bonds And Notes [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	0	0
Debt Securities, Available-for-sale, Noncurrent	0
US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	102,615	117,374
Debt Securities, Available-for-sale, Noncurrent	59,608
US Government Debt Securities [Member] | Quoted Prices In Active Markets For Identical Securities (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	0	0
Debt Securities, Available-for-sale, Noncurrent	0
US Government Debt Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	102,615	117,374
Debt Securities, Available-for-sale, Noncurrent	59,608
US Government Debt Securities [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	0	0
Debt Securities, Available-for-sale, Noncurrent	0
US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	27,087	47,151
Debt Securities, Available-for-sale, Noncurrent	8,952
US Government Agencies Debt Securities [Member] | Quoted Prices In Active Markets For Identical Securities (Level 1) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	0	0
Debt Securities, Available-for-sale, Noncurrent	0
US Government Agencies Debt Securities [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	27,087	47,151
Debt Securities, Available-for-sale, Noncurrent	8,952
US Government Agencies Debt Securities [Member] | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Debt Securities, Available-for-sale, Current	0	$ 0
Debt Securities, Available-for-sale, Noncurrent	$ 0

Fair Value Measurements - Sch_2

Fair Value Measurements - Schedule of Impairment Charges by Income Statement Line Item (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Property, Plant and Equipment [Line Items]
Impairment of assets	$ 40,698	$ 9,673	$ 6,273
Cost of net product revenue
Property, Plant and Equipment [Line Items]
Impairment of assets	2,865	241	0
Cost of net service revenue
Property, Plant and Equipment [Line Items]
Impairment of assets	3,492	1,034	0
Selling and Marketing Expense
Property, Plant and Equipment [Line Items]
Impairment of assets	11,515	2,876	0
Research and Development Expense
Property, Plant and Equipment [Line Items]
Impairment of assets	12,974	2,906	0
General and Administrative Expense
Property, Plant and Equipment [Line Items]
Impairment of assets	$ 9,852	$ 2,616	$ 6,273

Fair Value Measurements - Impai

Fair Value Measurements - Impairment of Assets Measured at Fair Value on a Nonrecurring Basis Narrative (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Operating Lease, Impairment Loss	$ 23.5	$ 6.7	$ 9.7
Fair Value, Nonrecurring | Fair Value, Inputs, Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Operating Lease, Impairment Loss	23.5	6.7	$ 9.7
Tangible Asset Impairment Charges	$ 10.3	$ 0.2
Capitalized Computer Software, Impairments				$ 6.3

Short-Term And Long-Term Inve_3

Short-Term And Long-Term Investments - Schedule Of Short-Term And Long-Term Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Short-Term Investments
Schedule of Investments [Line Items]
Cost or Amortized Cost	$ 329,571	$ 359,586
Gross Unrealized Gains	129	756
Gross Unrealized Losses	(70)	(9)
Fair Value	329,630	360,333
Short-Term Investments | Certificates of Deposit [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	255
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	255
Short-Term Investments | Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	186,043	188,932
Gross Unrealized Gains	116	736
Gross Unrealized Losses	(52)	(6)
Fair Value	186,107	189,662
Short-Term Investments | Municipal Bonds And Notes [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	13,570	6,143
Gross Unrealized Gains	1	3
Gross Unrealized Losses	(5)	0
Fair Value	13,566	6,146
Short-Term Investments | US Government Debt Securities [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	102,607	117,363
Gross Unrealized Gains	12	14
Gross Unrealized Losses	(4)	(3)
Fair Value	102,615	117,374
Short-Term Investments | US Government Agencies Debt Securities [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	27,096	47,148
Gross Unrealized Gains	0	3
Gross Unrealized Losses	(9)	0
Fair Value	27,087	47,151
Long-Term Investments
Schedule of Investments [Line Items]
Cost or Amortized Cost	132,813	102,206
Gross Unrealized Gains	16	756
Gross Unrealized Losses	(51)	(23)
Fair Value	132,778	102,939
Long-Term Investments | Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	53,128	102,206
Gross Unrealized Gains	13	756
Gross Unrealized Losses	(34)	(23)
Fair Value	53,107	$ 102,939
Long-Term Investments | Municipal Bonds And Notes [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	11,114
Gross Unrealized Gains	1
Gross Unrealized Losses	(4)
Fair Value	11,111
Long-Term Investments | US Government Debt Securities [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	59,614
Gross Unrealized Gains	2
Gross Unrealized Losses	(8)
Fair Value	59,608
Long-Term Investments | US Government Agencies Debt Securities [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	8,957
Gross Unrealized Gains	0
Gross Unrealized Losses	(5)
Fair Value	$ 8,952

Short-Term And Long-Term Inve_4

Short-Term And Long-Term Investments - Schedule Of Investments That Have Been In A Continuous Unrealized Loss Position (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Fair Value
Less Than 12 Months	$ 274,535	$ 85,304
12 Months or Greater	0	5,006
Total	274,535	90,310
Gross Unrealized Losses
Less Than 12 Months	(121)	(31)
12 Months or Greater	0	(1)
Total	(121)	(32)
Corporate Debt Securities [Member]
Fair Value
Less Than 12 Months	151,986	43,492
12 Months or Greater	0	5,006
Total	151,986	48,498
Gross Unrealized Losses
Less Than 12 Months	(86)	(28)
12 Months or Greater	0	(1)
Total	(86)	(29)
Municipal Bonds And Notes [Member]
Fair Value
Less Than 12 Months	13,764
12 Months or Greater	0
Total	13,764
Gross Unrealized Losses
Less Than 12 Months	(9)
12 Months or Greater	0
Total	(9)
US Government Debt Securities [Member]
Fair Value
Less Than 12 Months	77,401	41,812
12 Months or Greater	0	0
Total	77,401	41,812
Gross Unrealized Losses
Less Than 12 Months	(12)	(3)
12 Months or Greater	0	0
Total	(12)	$ (3)
US Government Agencies Debt Securities [Member]
Fair Value
Less Than 12 Months	31,384
12 Months or Greater	0
Total	31,384
Gross Unrealized Losses
Less Than 12 Months	(14)
12 Months or Greater	0
Total	$ (14)

Short-Term And Long-Term Inve_5

Short-Term And Long-Term Investments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Investment Income, Interest	$ 2.5	$ 12.2	$ 25.3

Balance Sheet Details - Cash, C

Balance Sheet Details - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Balance Sheet Details [Abstract]
Cash and Cash Equivalents, at Carrying Value	$ 580,977	$ 849,556
Restricted Cash	3,356	3,270
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 584,333	$ 852,826	$ 602,254	$ 425,894

Balance Sheet Details - Invento

Balance Sheet Details - Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Balance Sheet Details [Abstract]
Finished goods	$ 13,081	$ 17,096
Raw materials	8,974	10,802
Inventory, Net	$ 22,055	$ 27,898

Balance Sheet Details - Other C

Balance Sheet Details - Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Balance Sheet Details [Abstract]
Unbilled receivables	$ 215,396	$ 138,096
Prepaid expenses	59,636	47,197
Capitalized contract acquisition costs	34,265	29,650
Other	28,605	44,563
Other Assets, Current	$ 337,902	$ 259,506

Balance Sheet Details - Propert

Balance Sheet Details - Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Balance Sheet Details [Abstract]
Machinery and Equipment, Gross	$ 166,846	$ 153,256
Capitalized Computer Software, Gross	94,169	95,288
Furniture and Fixtures, Gross	45,204	45,280
Leasehold Improvements, Gross	174,504	175,593
Property, Plant and Equipment, Gross	480,723	469,417
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(289,559)	(240,178)
Property, Plant and Equipment, Net	$ 191,164	$ 229,239

Balance Sheet Details - Goodwil

Balance Sheet Details - Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Balance Sheet Details [Abstract]
Goodwill, Beginning Balance	$ 1,858,966	$ 1,065,379
Goodwill, Acquired During Period	351,417	799,611
Goodwill, Other Increase (Decrease)	6,170	(6,024)
Goodwill, Ending Balance	$ 2,216,553	$ 1,858,966

Balance Sheet Details - Other A

Balance Sheet Details - Other Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Balance Sheet Details [Abstract]
Intangible assets	$ 237,178	$ 225,900
Unbilled receivables	158,885	62,377
Capitalized contract acquisition costs	43,571	40,746
Other	32,924	18,424
Other Assets, Noncurrent	$ 472,558	$ 347,447

Balance Sheet Details - Intangi

Balance Sheet Details - Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 394,908	$ 334,908
Accumulated Amortization	(157,730)	(109,008)
Net Carrying Amount	237,178	225,900
Amortization of Intangible Assets	48,700	34,600	$ 11,800
Developed Technology Rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	305,673	246,173
Accumulated Amortization	(111,279)	(76,556)
Net Carrying Amount	194,394	169,617
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	41,742	41,242
Accumulated Amortization	(17,865)	(10,657)
Net Carrying Amount	23,877	30,585
Patents And Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	20,260	20,260
Accumulated Amortization	(17,180)	(14,448)
Net Carrying Amount	3,080	5,812
Trade Names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	24,973	24,973
Accumulated Amortization	(9,146)	(5,174)
Net Carrying Amount	15,827	19,799
Non-Compete Covenants [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2,260	2,260
Accumulated Amortization	(2,260)	(2,173)
Net Carrying Amount	$ 0	$ 87

Balance Sheet Details - Estimat

Balance Sheet Details - Estimated Amortization Expense For Intangible Assets (Details) $ in Thousands	Sep. 30, 2021USD ($)
Balance Sheet Details [Abstract]
2022	$ 50,095
2023	49,125
2024	43,860
2025	38,124
2026	32,860
Total estimated amortization expense	$ 214,064

Balance Sheet Details - Accrued

Balance Sheet Details - Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Balance Sheet Details [Abstract]
Payroll and benefits	$ 179,147	$ 169,708
Operating lease liabilities, current	49,286	46,010
Income and other tax accruals	44,075	33,048
Other	68,979	72,632
Accrued Liabilities, Current	$ 341,487	$ 321,398

Balance Sheet Details - Other L

Balance Sheet Details - Other Long-term Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Balance Sheet Details [Abstract]
Income taxes payable	$ 66,081	$ 49,846
Other	9,155	9,665
Other Liabilities, Noncurrent	$ 75,236	$ 59,511

Balance Sheet Details - Narrati

Balance Sheet Details - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Property, Plant and Equipment [Line Items]
Depreciation and amortization			$ 115,424	$ 95,857	$ 68,507
Fair Value, Inputs, Level 3 | Fair Value, Nonrecurring
Property, Plant and Equipment [Line Items]
Tangible Asset Impairment Charges	$ 10,300	$ 200
Capitalized Computer Software, Impairments					6,300
Property, Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization			$ 61,300	$ 59,500	$ 58,000

Debt Facilities - Long-term Deb

Debt Facilities - Long-term Debt Maturities (Details) - Term Loan Facility [Member] $ in Thousands	Sep. 30, 2021USD ($)
Debt Instrument [Line Items]
2022	$ 20,000
2023	350,000
Total	$ 370,000

Debt Facilities - Narrative (De

Debt Facilities - Narrative (Details)	Jan. 31, 2020USD ($)	Jan. 24, 2020USD ($)	Sep. 30, 2021USD ($)extension	Sep. 30, 2020
Term Loan Facility [Member]
Debt Instrument [Line Items]
Aggregate Principal Amount		$ 400,000,000
Debt Issuance Costs		$ 2,200,000	$ 1,000,000
Redemption Percentage		1.25%
Long-term Debt			$ 370,000,000
Interest Rate at Period End			1.361%	2.365%
Term Loan Facility [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument [Line Items]
Basis Spread on Variable Rate			1.125%
Term Loan Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum
Debt Instrument [Line Items]
Basis Spread on Variable Rate		1.125%
Term Loan Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum
Debt Instrument [Line Items]
Basis Spread on Variable Rate		1.75%
Term Loan Facility [Member] | Alternate Base Rate [Member]
Debt Instrument [Line Items]
Basis Spread on Variable Rate			0.125%
Term Loan Facility [Member] | Alternate Base Rate [Member] | Minimum
Debt Instrument [Line Items]
Basis Spread on Variable Rate		0.125%
Term Loan Facility [Member] | Alternate Base Rate [Member] | Maximum
Debt Instrument [Line Items]
Basis Spread on Variable Rate		0.75%
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Aggregate Principal Amount	$ 350,000,000
Conditional Increase In Borrowing Capacity	$ 150,000,000
Number Of Extensions | extension			2
Length Of Extension Period			1 year
Long-term Line of Credit			$ 0
Outstanding Line of Credit Balance			$ 350,000,000
Revolving Credit Facility [Member] | Minimum
Debt Instrument [Line Items]
Commitment Fee Percentage	0.125%
Revolving Credit Facility [Member] | Maximum
Debt Instrument [Line Items]
Commitment Fee Percentage	0.30%
Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.125%
Revolving Credit Facility [Member] | London Interbank Offered Rate (LIBOR) [Member] | Maximum
Debt Instrument [Line Items]
Basis Spread on Variable Rate	1.75%
Revolving Credit Facility [Member] | Alternate Base Rate [Member] | Minimum
Debt Instrument [Line Items]
Basis Spread on Variable Rate	0.125%
Revolving Credit Facility [Member] | Alternate Base Rate [Member] | Maximum
Debt Instrument [Line Items]
Basis Spread on Variable Rate	0.75%

Leases - Operating Lease Expens

Leases - Operating Lease Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Operating lease expense	$ 47,993	$ 49,925
Short-term lease expense	2,953	3,563
Variable lease expense	25,200	21,980
Total lease expense	$ 76,146	$ 75,468

Leases - Supplemental Balance S

Leases - Supplemental Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Operating lease right-of-use assets	$ 244,934	$ 300,680
Operating Lease, Liability, Current	49,286	46,010
Operating lease liabilities, long-term	296,945	338,715
Total lease liabilities	$ 346,231	$ 384,725
Weighted average remaining lease term (in years)	9 years 8 months 12 days	10 years 2 months 12 days
Weighted average discount rate	2.60%	2.58%

Leases - Maturities of Lease Li

Leases - Maturities of Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
2022	$ 57,849
2023	48,458
2024	41,142
2025	33,600
2026	26,609
Thereafter	191,142
Total lease payments	398,800
Less: imputed interest	(52,569)
Total lease liabilities	$ 346,231	$ 384,725

Leases - Operating Lease Future

Leases - Operating Lease Future Minimum ASC 840 (Details) $ in Thousands	Sep. 30, 2019USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2020	$ 54,046
2021	50,712
2022	47,550
2023	36,514
2024	33,971
Thereafter	242,826
Gross Lease Payments, Total	465,619
Operating Leases, Future Minimum Payments Receivable [Abstract]
2020	683
2021	1,051
2022	1,082
2023	368
2024	0
Thereafter	0
Operating Leases, Future Minimum Payments Receivable	3,184
Future Minimum Operating Net Lease Payments Fiscal Year Maturity [Abstract]
2020	53,363
2021	49,661
2022	46,468
2023	36,146
2024	33,971
Thereafter	242,826
Net Lease Payments, Total	$ 462,435

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2021USD ($)	Dec. 31, 2020USD ($)	Sep. 30, 2021USD ($)ft²	Sep. 30, 2020USD ($)	Oct. 01, 2019USD ($)
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets			$ 244,934	$ 300,680
Operating Lease, Impairment Loss	$ 23,500	$ 6,700		$ 9,700
Sublease Income			13,000
Lessor, Operating Lease, Payments to be Received, Next Twelve Months			5,700
Lessor, Operating Lease, Payments to be Received, Two To Four Years			$ 7,300
Office Building [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Number of Square Feet | ft²			515,000
Accounting Standards Update 2016-02 [Member]
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets					$ 304,800
Lease Liabilities					$ 386,400

Income Taxes - Components Of In

Income Taxes - Components Of Income Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
United States	$ 189,398	$ 216,409	$ 360,648
International	197,539	179,988	180,463
Income before income taxes	$ 386,937	$ 396,397	$ 541,111

Income Taxes - Schedule Of Prov

Income Taxes - Schedule Of Provision For Income Taxes (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Current, U.S. federal	$ 53,107	$ 26,978	$ 43,039
Current, State	16,686	4,230	13,864
Current, Foreign	62,832	50,368	49,197
Total	132,625	81,576	106,100
Deferred, U.S. federal	(61,739)	10,875	8,716
Deferred, State	(15,294)	(1,121)	1,617
Deferred, Foreign	104	(2,374)	(3,056)
Total	(76,929)	7,380	7,277
Income taxes (benefit)	$ 55,696	$ 88,956	$ 113,377

Income Taxes - Schedule Of Effe

Income Taxes - Schedule Of Effective Tax Rate Differs From The U.S. Federal Statutory Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income tax provision at statutory rate	$ 81,257	$ 83,243	$ 113,633
State taxes, net of federal benefit	5,118	4,258	14,206
Tax impact of foreign operations	(26,881)	(7,693)	(9,161)
Research and development and other credits	(18,055)	(11,843)	(12,760)
Stock-based and other compensation	12,740	18,002	6,771
Other	1,517	2,989	688
Income taxes (benefit)	$ 55,696	$ 88,956	$ 113,377

Income Taxes - Schedule Of Tax

Income Taxes - Schedule Of Tax Effects To Deferred Tax Assets And Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Sep. 30, 2020
Income Tax Disclosure [Abstract]
Net operating loss carry-forwards	$ 41,252	$ 54,842
Capitalized research and development costs	95,259	0
Accrued compensation and benefits	13,207	13,162
Stock-based compensation	12,829	13,010
Deferred revenue	30,115	40,577
Lease liabilities	23,747	19,656
Other accruals and reserves	18,450	17,384
Tax credit carryforwards	34,187	15,807
Depreciation	580	620
Total deferred tax assets before deferred liabilities	269,626	175,058
Valuation allowance	(40,404)	(32,587)
Deferred tax assets, net of valuation allowance	229,222	142,471
Purchased intangibles	(57,219)	(46,491)
Depreciation	(26,516)	(34,757)
Deferred Tax Liabilities, Deferred Expense, Other Capitalized Costs	(13,057)	(11,924)
Deferred Tax Liabilities, Deferred Expense, Reserves and Accruals	(6,651)	(4,728)
Total deferred tax liabilities	(103,443)	(97,900)
Net deferred tax assets	$ 125,779	$ 44,571

Income Taxes - Schedule Of Reco

Income Taxes - Schedule Of Reconciliation Of Beginning And Ending Amount Of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance, beginning of period	$ 51,767	$ 42,287	$ 31,672
Gross increases related to prior period tax positions	14,867	8,664	5,129
Gross decreases related to prior period tax positions	0	(1,051)	(287)
Gross increases related to current period tax positions	12,595	9,272	7,756
Decreases relating to settlements with tax authorities	(321)	(3,578)	0
Reductions due to lapses of statute of limitations	(8,094)	(3,827)	(1,983)
Balance, end of period	$ 70,814	$ 51,767	$ 42,287

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Operating Loss Carryforwards [Line Items]
Income Tax Holiday, Aggregate Dollar Amount	$ 6,000	$ 8,200	$ 8,100
Income Tax Holiday, Income Tax Benefits Per Share	$ 0.10	$ 0.13	$ 0.13
Deferred Tax Assets, Operating Loss Carryforwards	$ 41,252	$ 54,842
Deferred Tax Assets, Tax Credit Carryforwards	34,187	15,807
Valuation Allowance, Deferred Tax Asset, Change in Amount	7,800	9,100
Unrecognized Tax Benefits	70,814	51,767	$ 42,287	$ 31,672
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	39,200	34,300	29,400
Unrecognized Tax Benefits, Period Increase (Decrease)	1,400	(1,000)	$ 2,400
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	4,400	$ 3,000
Foreign [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry-forwards, net	61,300
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	2,700
Deferred Tax Assets, Tax Credit Carryforwards	3,300
Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry-forwards, net	82,900
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	9,900
Deferred Tax Assets, Operating Loss Carryforwards	92,800
Deferred Tax Assets, Tax Credit Carryforwards	9,500
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry-forwards, net	292,000
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	184,100
Deferred Tax Assets, Operating Loss Carryforwards	476,100
Deferred Tax Assets, Tax Credit Carryforwards	25,700
Deferred Tax Assets, Tax Credit Carryforwards, Subject to Expiration	$ 3,300

Shareholders' Equity - Narrativ

Shareholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2021	Sep. 30, 2021	Feb. 03, 2021	Oct. 31, 2018	Oct. 25, 2017
Common Stock Repurchase [Line Items]
Accelerated Share Repurchases, Settlement (Payment) or Receipt		$ 400			$ 500
Treasury Stock Acquired, Average Cost Per Share		$ 194.91	$ 199.90
Accelerated Share Repurchases, Cash or Stock Settlement	449,049	2.1 million	2.5 million
Adjustments To Additional Paid In Capital, Equity Forward Contract	$ 100
Stock Repurchase Program, Remaining Authorized Repurchase Amount				$ 773
October Twenty Six Two Thousand Ten Program [Member]
Common Stock Repurchase [Line Items]
Stock Repurchase Program, Authorized Amount						$ 1,000	$ 4,400

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions (Details)	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Fair Value Assumptions
Expected dividend	0.00%	0.00%	0.00%
Expected term	6 months	6 months	6 months
Minimum
Fair Value Assumptions
Risk-free interest rate	0.07%	1.10%	2.25%
Expected volatility	29.67%	26.32%	18.14%
Maximum
Fair Value Assumptions
Risk-free interest rate	0.13%	1.97%	2.51%
Expected volatility	37.22%	41.94%	31.74%
Two Thousand Eleven Employee Stock Purchase Plan [Member]
Fair Value Assumptions
Expected term	6 months

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule Of Summary Of Restricted Stock Unit Activity (Details)	12 Months Ended
	Sep. 30, 2021$ / sharesshares
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning balance	$ 137.84
Weighted Average Grant Date Fair Value, Ending balance	$ 145.89
Performance Shares [Member] | Two Thousand Fourteen Equity Incentive Plan [Member]
Outstanding Restricted Stock Units
Outstanding Stock Units, Beginning balance | shares	145,869
Outstanding Stock Units, Units granted | shares	153,434
Outstanding Stock Units, Units vested | shares	(59,365)
Outstanding Stock Units, Units cancelled | shares	(9,012)
Outstanding Stock Units, Ending balance | shares	230,926
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning balance	$ 146.42
Weighted Average Grant Date Fair Value, Units granted	117.16
Weighted Average Grant Date Fair Value, Units vested	137.13
Weighted Average Grant Date Fair Value, Units cancelled	162.72
Weighted Average Grant Date Fair Value, Ending balance	$ 136.47
Restricted Stock Units (RSUs) [Member] | Two Thousand Fourteen Equity Incentive Plan [Member]
Outstanding Restricted Stock Units
Outstanding Stock Units, Beginning balance | shares	1,204,290
Outstanding Stock Units, Units granted | shares	1,510,829
Outstanding Stock Units, Units vested | shares	(1,183,086)
Outstanding Stock Units, Units cancelled | shares	(191,485)
Outstanding Stock Units, Ending balance | shares	1,340,548
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning balance	$ 146.39
Weighted Average Grant Date Fair Value, Units granted	137.33
Weighted Average Grant Date Fair Value, Units vested	183.01
Weighted Average Grant Date Fair Value, Units cancelled	138.09
Weighted Average Grant Date Fair Value, Ending balance	$ 141.90

Stock-Based Compensation - Sc_3

Stock-Based Compensation - Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions (Details) - $ / shares	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	6 months	6 months	6 months
Expected dividend	0.00%	0.00%	0.00%
Tranche 1 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair Value, Per Share	$ 182.01
Expected term	10 months 28 days
Risk-free interest rate	0.13%
Expected dividend	0.00%
Tranche 1 [Member] | F5 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	41.89%
Tranche 1 [Member] | Index Members [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	53.54%
Tranche 2 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair Value, Per Share	$ 185.86
Expected term	1 year 10 months 28 days
Risk-free interest rate	0.16%
Expected dividend	0.00%
Tranche 2 [Member] | F5 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	34.77%
Tranche 2 [Member] | Index Members [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	41.85%
Tranche 3 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair Value, Per Share	$ 189.57
Expected term	2 years 10 months 28 days
Risk-free interest rate	0.20%
Expected dividend	0.00%
Tranche 3 [Member] | F5 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	31.74%
Tranche 3 [Member] | Index Members [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	37.45%

Stock-Based Compensation - Sc_4

Stock-Based Compensation - Schedule of Nonvested Restricted Stock Units Activity (Details) - Restricted Stock Units (RSUs) [Member] - shares	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	2 years	2 years	2 years
Annual Equity Program [Member] | November 2, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity Instruments Other than Options, Grants in Period	257,568
Award vesting period	3 years
Annual Equity Program [Member] | November 1, 2019 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity Instruments Other than Options, Grants in Period	228,616
Award vesting period	3 years
Annual Equity Program [Member] | November 1, 2018 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity Instruments Other than Options, Grants in Period	144,066
Award vesting period	3 years
Annual Equity Program [Member] | November 1, 2017 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity Instruments Other than Options, Grants in Period	140,135
Award vesting period	4 years

Stock-Based Compensation - Sc_5

Stock-Based Compensation - Schedule Of Stock Option Activity (Details)	12 Months Ended
	Sep. 30, 2021$ / sharesshares
Number of Shares
Number of Shares, Beginning balance | shares	391,100
Number of Shares, Options granted | shares	145,360
Number of Shares, Options exercised | shares	(163,880)
Number of Shares, Options cancelled | shares	(47,956)
Number of Shares, Ending balance | shares	324,624
Weighted Average Exercise Price per Share
Weighted Average Exercise Price per Share, Beginning balance | $ / shares	$ 36.71
Weighted Average Exercise Price per Share, Options granted | $ / shares	14.84
Weighted Average Exercise Price per Share, Options exercised | $ / shares	29.68
Weighted Average Exercise Price per Share, Options cancelled | $ / shares	34.21
Weighted Average Exercise Price per Share, Ending balance | $ / shares	$ 30.83

Stock-Based Compensation - Sc_6

Stock-Based Compensation - Schedule Of Outstanding Stock Options Currently Exercisable, Vested And Expected To Vest (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Share-based Payment Arrangement, Noncash Expense [Abstract]
Stock options outstanding	324,624	391,100
Stock options outstanding, Weighted Average Remaining Contractual Life (in Years)	7 years 2 months 8 days
Stock options outstanding, Weighted Average Exercise Price per Share	$ 30.83	$ 36.71
Stock options outstanding, Aggregate Intrinsic Value	$ 54,520
Exercisable, Number of Shares	158,544
Exercisable, Weighted Average Remaining Contractual Life (in Years)	6 years 8 months 1 day
Exercisable, Weighted Average Exercise Price per Share	$ 28.15
Exercisable, Aggregate Intrinsic Value	$ 27,052
Vested and expected to vest, Number of Shares	313,777
Vested and expected to vest, Weighted Average Remaining Contractual Life (in Years)	7 years 1 month 28 days
Vested and expected to vest, Weighted Average Exercise Price per Share	$ 30.53
Vested and expected to vest, Aggregate Intrinsic Value	$ 52,794

Stock-Based Compensation - Sc_7

Stock-Based Compensation - Schedule Of Equity Based Awards (Including Stock Options And Restricted Stock Units (Details) - Equity Based Awards [Member]	12 Months Ended
	Sep. 30, 2021shares
Awards Available for Grant
Awards Available for Grant, Beginning balance	2,714,958
Awards Available for Grant, Granted	(1,976,525)
Awards Available for Grant, Cancelled	299,248
Additional shares reserved (terminated), net	950,729
Awards Available for Grant, Ending balance	1,988,410

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($)	Oct. 29, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019	Jan. 22, 2021	Jan. 24, 2020	May 08, 2019	Mar. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Payment Arrangement, Expense		$ 243,300,000	$ 201,900,000	$ 162,900,000
Share-based Payment Arrangement, Expense, Tax Benefit		44,100,000	$ 37,600,000	$ 31,300,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount		$ 220,700,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition		2 years
Expected term		6 months	6 months	6 months
Weighted Average Grant Date Fair Value		$ 145.89	$ 137.84	$ 165.64
Fair market value of restricted stock vested		$ 261,900,000	$ 138,400,000	$ 159,600,000
Total intrinsic value of options exercised		$ 25,600,000	$ 11,400,000	$ 700,000
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity Instruments Other than Options, Grants in Period	881,908
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period		2 years	2 years	2 years
Two Thousand Eleven Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance		10,000,000
Percentage of base compensation for which employees can acquire shares of common stock		15.00%
Maximum shares allowed for purchase by employee in period		10,000
Maximum aggregate fair value of stock that an employee may purchase		$ 25,000
Expected term		6 months
Percentage of common stock lesser of the fair market value		85.00%
Number of Shares Authorized		1,356,896
Traffix 2007 Plan [Member] [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance								106,829
Shares available for purchase under stock option plan		49
Nginx Acquisition Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance							183,061
Vesting rate of stock options and awards upon certain changes in ownership control		50.00%
Nginx Acquisition Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding stock units		71,302
Nginx, Inc. 2011 Share Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance							302,634
Nginx, Inc. 2011 Share Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding stock units		9,242
Nginx, Inc. 2011 Share Plan [Member] | Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for purchase under stock option plan		68,095
Shape Acquisition Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance						450,000
Vesting rate of stock options and awards upon certain changes in ownership control		50.00%
Shape Acquisition Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding stock units		210,720
Shape 2011 Share Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance						501,085
Shape 2011 Share Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Outstanding stock units		3,755
Shape 2011 Share Plan [Member] | Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for purchase under stock option plan		140,033
Volterra Acquisition Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance					140,000
Vesting rate of stock options and awards upon certain changes in ownership control		50.00%
Volterra Acquisition Equity Incentive Plan | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued in Period		122,056
Outstanding stock units		121,036
Volterra 2017 Stock Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance					261,696
Volterra 2017 Stock Plan | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued in Period		44,846
Outstanding stock units		34,863
Volterra 2017 Stock Plan | Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued in Period		145,360
Shares available for purchase under stock option plan		116,447
Two Thousand Fourteen Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance		22,180,000
Vesting rate of stock options and awards upon certain changes in ownership control		50.00%
Number of Shares Authorized		1,889,511
Two Thousand Fourteen Equity Incentive Plan [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued in Period		153,434
Outstanding stock units		230,926	145,869
Weighted Average Grant Date Fair Value		$ 136.47	$ 146.42
Equity Instruments Other than Options, Grants in Period		153,434
Two Thousand Fourteen Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued in Period		1,510,829
Outstanding stock units		1,340,548	1,204,290
Weighted Average Grant Date Fair Value		$ 141.90	$ 146.39
Equity Instruments Other than Options, Grants in Period		1,510,829

Net Income Per Share (Details)

Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Net Income Per Share [Abstract]
Net income	$ 331,241	$ 307,441	$ 427,734
Weighted average shares - basic (shares)	60,707	60,911	60,044
Weighted Average Number Diluted Shares Outstanding Adjustment	1,350	467	412
Weighted Average Number of Shares Outstanding, Diluted	62,057	61,378	60,456
Net income per share - basic (USD per share)	$ 5.46	$ 5.05	$ 7.12
Net income per share - diluted (USD per share)	$ 5.34	$ 5.01	$ 7.08

Commitments And Contingencies -

Commitments And Contingencies - Narrative (Details) $ in Millions	Sep. 30, 2021USD ($)
Purchase Commitment [Member]
Commitments And Contingencies [Line Items]
Purchase Commitment, Remaining Minimum Amount Committed	$ 26.4

Restructuring Charges (Details)

Restructuring Charges (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2020USD ($)employee	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)
Restructuring and Related Activities [Abstract]
Number of Employees in Reduction of Force Program | employee	75
Restructuring charges | $	$ 7,800	$ 0	$ 7,800	$ 0

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Contributions by the Company to the plan	$ 13.2	$ 11.3	$ 10.5
Employer contribution, vesting period	4 years	4 years	4 years

Segment Information (Details)

Segment Information (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2021USD ($)segmentgeographic_region	Sep. 30, 2020USD ($)segmentgeographic_region	Sep. 30, 2019USD ($)geographic_regionsegment
Segment Reporting Information [Line Items]
Number of Reportable Segments | segment	1	1	1
Number of Geographic Regions | geographic_region	3	3	3
Net revenues	$ 2,603,416	$ 2,350,822	$ 2,242,447
Property and equipment, net	191,164	229,239
Product [Member]
Segment Reporting Information [Line Items]
Net revenues	1,247,084	1,025,856	985,591
Product [Member] | Systems
Segment Reporting Information [Line Items]
Net revenues	748,192	668,313	745,798
Product [Member] | Software
Segment Reporting Information [Line Items]
Net revenues	498,892	357,543	239,793
United States [Member]
Segment Reporting Information [Line Items]
Net revenues	1,365,625	1,221,190	1,137,556
Property and equipment, net	153,030	190,509
Other Americas [Member]
Segment Reporting Information [Line Items]
Net revenues	92,111	95,878	108,112
Americas [Member]
Segment Reporting Information [Line Items]
Net revenues	1,457,736	1,317,068	1,245,668
EMEA [Member]
Segment Reporting Information [Line Items]
Net revenues	667,219	593,307	553,701
Property and equipment, net	20,526	20,361
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net revenues	478,461	440,447	$ 443,078
Other International Countries [Member]
Segment Reporting Information [Line Items]
Property and equipment, net	$ 17,608	$ 18,369
Customer One [Member] | Geographic Concentration Risk [Member] | Revenue Benchmark [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage	19.20%	16.70%	18.20%
Customer One [Member] | Geographic Concentration Risk [Member] | Accounts Receivable [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage	12.60%	14.10%
Customer Two [Member] | Geographic Concentration Risk [Member] | Revenue Benchmark [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage	0.00%	0.00%	10.20%
Customer Three [Member] | Geographic Concentration Risk [Member] | Revenue Benchmark [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage	0.00%	0.00%	10.00%
Customer Four [Member] | Geographic Concentration Risk [Member] | Revenue Benchmark [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage	11.10%	0.00%	0.00%
Customer Four [Member] | Geographic Concentration Risk [Member] | Accounts Receivable [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage	11.90%	11.40%
Customer Five [Member] | Geographic Concentration Risk [Member] | Accounts Receivable [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage	11.50%	0.00%

Subsequent Events (Details)

Subsequent Events (Details) - Threat Stack, Inc. - USD ($) $ in Millions	Oct. 01, 2021	Sep. 30, 2021
Subsequent Event [Line Items]
Transaction Costs		$ 1.7
Subsequent Event [Member]
Subsequent Event [Line Items]
Total Purchase Price	$ 68

Uncategorized Items - ffiv-2021

Label	Element	Value
Accounting Standards Update 2014-09 [Member]
Stockholders' Equity, Other	us-gaap_StockholdersEquityOther	$ 36,048,000
Accounting Standards Update 2014-09 [Member] | Retained Earnings [Member]
Stockholders' Equity, Other	us-gaap_StockholdersEquityOther	$ 36,048,000