F5 (FFIV) 10-K 19 Nov 20 2020 FY Annual report Financial data

Cover Page

Cover Page - USD ($)	12 Months Ended
	Sep. 30, 2020	Nov. 09, 2020	Mar. 31, 2020
Cover [Abstract]
Entity Central Index Key	0001048695
Document Type	10-K
Document Annual Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	000-26041
Entity Registrant Name	F5 Networks, 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
Entity Shell Company	false
Entity Public Float			$ 6,445,848,331
Entity Common Stock, Shares Outstanding		61,603,102
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 2020, 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
Current Fiscal Year End Date	--09-30
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Amendment Flag	false

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
ASSETS
Cash and cash equivalents	$ 849,556	$ 599,219
Short-term investments	360,333	373,063
Accounts receivable, net of allowances of $3,105 and $3,259	296,183	322,029
Inventories	27,898	34,401
Other current assets	259,506	182,874
Total current assets	1,793,476	1,511,586
Property and equipment, net	229,239	223,426
Operating lease right-of-use assets	300,680	0
Long-term investments	102,939	358,402
Deferred tax assets	45,173	27,701
Goodwill	1,858,966	1,065,379
Other assets, net	347,447	203,781
Total assets	4,677,920	3,390,275
LIABILITIES AND SHAREHOLDERS’ EQUITY
Accounts payable	64,472	62,627
Accrued liabilities	321,398	235,869
Deferred revenue	883,134	807,030
Current portion of long-term debt	19,275	0
Total current liabilities	1,288,279	1,105,526
Deferred tax liabilities	602	313
Deferred revenue, long-term	389,498	391,086
Operating lease liabilities, long-term	338,715	0
Long-term debt	369,047	0
Other long-term liabilities	59,511	131,853
Total long-term liabilities	1,157,373	523,252
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, 61,099 and 60,367 shares issued and outstanding	305,453	142,597
Accumulated other comprehensive loss	(18,716)	(19,190)
Retained earnings	1,945,531	1,638,090
Total shareholders’ equity	2,232,268	1,761,497
Total liabilities and shareholders’ equity	$ 4,677,920	$ 3,390,275
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, par value (USD per share)	$ 0	$ 0
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 outstanding	61,099,000	60,367,000

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Statement of Financial Position [Abstract]
Accounts receivable, allowances	$ 3,105	$ 3,259
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	61,099,000	60,367,000
Common stock, shares outstanding	61,099,000	60,367,000

Consolidated Income Statements

Consolidated Income Statements - USD ($) shares in Thousands, $ in Thousands	3 Months Ended									12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Net revenues
Net revenues	$ 614,816	$ 583,252	$ 583,449	$ 569,305	$ 590,388	$ 563,394	$ 544,895	$ 543,770		$ 2,350,822	$ 2,242,447	$ 2,161,407
Cost of net revenues
Cost of net revenues	111,967	106,040	101,238	88,642	90,918	90,767	88,178	86,714		407,887	356,577	361,481
Gross profit	502,849	477,212	482,211	480,663	499,470	472,627	456,717	457,056		1,942,935	1,885,870	1,799,926
Operating expenses
Sales and marketing	220,379	211,808	215,472	195,519	217,554	195,852	170,954	164,259		843,178	748,619	664,135
Research and development	120,300	115,991	109,028	96,005	102,812	116,894	96,314	92,038		441,324	408,058	366,084
General and administrative	63,557	61,792	74,013	59,004	64,390	57,141	46,656	42,543		258,366	210,730	160,382
Restructuring charges	0	0	0	7,800	0	0	0	0	$ 18,400	7,800	0	18,426
Total	404,236	389,591	398,513	358,328	384,756	369,887	313,924	298,840		1,550,668	1,367,407	1,209,027
Income from operations	98,613	87,621	83,698	122,335	114,714	102,740	142,793	158,216		392,267	518,463	590,899
Other income, net	(1,090)	141	(141)	5,220	3,397	4,722	7,434	7,095		4,130	22,648	12,861
Income before income taxes	97,523	87,762	83,557	127,555	118,111	107,462	150,227	165,311		396,397	541,111	603,760
Provision for income taxes	19,860	17,890	22,178	29,028	23,274	21,557	34,140	34,406		88,956	113,377	150,071
Net income	$ 77,663	$ 69,872	$ 61,379	$ 98,527	$ 94,837	$ 85,905	$ 116,087	$ 130,905		$ 307,441	$ 427,734	$ 453,689
Net income per share - basic (USD per share)	$ 1.27	$ 1.15	$ 1.01	$ 1.62	$ 1.57	$ 1.43	$ 1.94	$ 2.17		$ 5.05	$ 7.12	$ 7.41
Weighted average shares - basic (shares)	61,149	60,978	60,869	60,649	60,283	59,981	59,686	60,216		60,911	60,044	61,262
Net income per share - diluted (USD per share)	$ 1.26	$ 1.14	$ 1	$ 1.62	$ 1.57	$ 1.43	$ 1.93	$ 2.16		$ 5.01	$ 7.08	$ 7.32
Weighted average shares - diluted (shares)	61,636	61,415	61,084	60,815	60,448	60,196	60,029	60,645		61,378	60,456	62,013
Product [Member]
Net revenues
Net revenues	$ 278,451	$ 253,331	$ 259,538	$ 234,536	$ 264,926	$ 248,929	$ 237,859	$ 233,877		$ 1,025,856	$ 985,591	$ 960,108
Cost of net revenues
Cost of net revenues	62,634	57,437	53,086	42,118	44,693	44,336	43,547	42,410		215,275	174,986	181,061
Service [Member]
Net revenues
Net revenues	336,365	329,921	323,911	334,769	325,462	314,465	307,036	309,893		1,324,966	1,256,856	1,201,299
Cost of net revenues
Cost of net revenues	$ 49,333	$ 48,603	$ 48,152	$ 46,524	$ 46,225	$ 46,431	$ 44,631	$ 44,304		$ 192,612	$ 181,591	$ 180,420

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income Statement - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income	$ 307,441	$ 427,734	$ 453,689
Other Comprehensive Income (Loss), Net of Tax [Abstract]
Foreign currency translation adjustment	(572)	(837)	(1,415)
Available-for-sale securities:
Unrealized gains (losses) on securities, net of taxes of $76, $954, and $(869) for the years ended September 30, 2020, 2019, and 2018, respectively	809	3,715	(2,775)
Reclassification adjustment for realized losses included in net income, net of taxes of $(65), $(35), and $(4) for the years ended September 30, 2020, 2019, and 2018, respectively	237	110	9
Net change in unrealized gains (losses) on available-for-sale securities, net of tax	1,046	3,825	(2,766)
Total other comprehensive income (loss)	474	2,988	(4,181)
Comprehensive income	$ 307,915	$ 430,722	$ 449,508

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	$ 76	$ 954	$ (869)
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	$ (65)	$ (35)	$ (4)

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, 2017		62,594,000
Balance at Sep. 30, 2017	$ 1,229,392	$ 17,627	$ (17,997)	$ 1,229,762
Exercise of employee stock options	3	$ 3
Exercise of employee stock options, shares		1,000
Issuance of stock under employee stock purchase plan	48,815	$ 48,815
Issuance of stock under employee stock purchase plan, shares		475,000
Issuance of restricted stock, shares		1,219,000
Repurchase of common stock	(600,081)	$ (203,873)		(396,208)
Repurchase of common stock, shares		(4,074,000)
Taxes paid related to net share settlement of equity awards	0
Stock-based compensation	157,855	$ 157,855
Net income	453,689			453,689
Other comprehensive income (loss)	(4,181)		(4,181)
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	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	104,487	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	(799,495)	(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

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Operating activities
Net income	$ 307,441	$ 427,734	$ 453,689
Adjustments to reconcile net income to net cash provided by operating activities:
Stock-based compensation	201,948	162,914	157,855
Depreciation and amortization	95,857	68,507	59,491
Non-cash operating lease costs	39,139	0	0
Deferred income taxes	7,293	7,440	20,810
Impairment of assets	9,673	6,273	0
Non-cash provisions for exit costs	0	8,211	0
Other	2,122	1,662	1,194
Changes in operating assets and liabilities (excluding effects of the acquisition of businesses):
Accounts receivable	46,502	(18,305)	(4,889)
Inventories	6,503	(3,832)	(734)
Other current assets	(49,895)	(75,449)	15,607
Other assets	(25,690)	(22,742)	446
Accounts payable and accrued liabilities	34,742	74,710	6,583
Deferred revenue	35,514	110,718	51,016
Lease liabilities	(50,251)	0	0
Net cash provided by operating activities	660,898	747,841	761,068
Investing activities
Purchases of investments	(584,240)	(602,987)	(855,424)
Maturities of investments	543,065	625,201	439,130
Sales of investments	309,687	278,244	12,736
Acquisition of businesses, net of cash acquired	(955,574)	(611,550)	0
Cash provided by sale of fixed assets	0	0	1,000
Purchases of property and equipment	(59,940)	(103,542)	(53,465)
Net cash used in investing activities	(747,002)	(414,634)	(456,023)
Financing activities
Proceeds from the exercise of stock options and purchases of stock under employee stock purchase plan	52,835	45,598	48,818
Repurchase of common stock	(100,016)	(201,045)	(600,081)
Proceeds from term debt agreement	400,000	0	0
Payments on term debt agreement	(10,000)	0	0
Payments for debt issuance costs	(3,040)	0	0
Taxes paid related to net share settlement of equity awards	(2,536)	0	0
Net cash provided by (used in) financing activities	337,243	(155,447)	(551,263)
Net increase (decrease) in cash, cash equivalents and restricted cash	251,139	177,760	(246,218)
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(567)	(1,400)	(2,340)
Cash, cash equivalents and restricted cash, beginning of year	602,254	425,894	674,452
Cash, cash equivalents and restricted cash, end of year	852,826	602,254	425,894
Supplemental disclosures of cash flow information
Cash paid for taxes, net of refunds	80,236	100,569	104,878
Cash paid for amounts included in the measurement of operating lease liabilities	60,564	0	0
Cash paid for interest on long-term debt	6,568	0	0
Supplemental disclosures of non-cash activities
Right-of-use assets obtained in exchange for lease obligations	402,007	0	0
Capitalized leasehold improvements paid directly by landlord	$ 0	$ 34,948	$ 9,958

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	12 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Summary Of Significant Accounting Policies	Summary of Significant Accounting Policies The Company F5 Networks, Inc. (the “Company”) is a leading provider of multi-cloud application services 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 24, 2020, the Company completed the acquisition of Shape Security, Inc. ("Shape"), a leader in online fraud and abuse prevention, adding protection from automated attacks, botnets, and targeted fraud to F5's world-class portfolio of application services. 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. Prior Period Reclassifications Certain prior year amounts have been reclassified to conform to the current year presentation in the Consolidated Statements of Cash Flows. The reclassified amounts are considered immaterial and there was no change to total cash from operating, investing or financing activities as a result. 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 and outcomes may differ from management's estimates and assumptions. In December 2019, a novel strain of coronavirus (“COVID-19“) was first identified, and in March 2020, the World Health Organization categorized COVID-19 as a pandemic. The Company assessed the impact that COVID-19 had on its results of operations, including, but not limited to an assessment of its allowance for doubtful accounts, the carrying value of short-term and long-term investments, the carrying value of goodwill and other long-lived assets, and the impact to revenue recognition and cost of revenues. The Company is actively monitoring the impact to the results of its business operations, and may make decisions required by federal, state or local authorities, or that are determined to be in the best interests of its employees, customers, partners, suppliers and stockholders. As of the filing date, the extent to which the COVID-19 pandemic may impact the Company’s financial condition or results of operations remains uncertain. 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 declines in value of securities judged to be other than temporary are included in other income (expense). 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. 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 doubtful accounts is recorded to account for potential bad debts. Estimates are used in determining the allowance for doubtful accounts and are based upon an assessment of selected accounts and as a percentage of remaining accounts receivable by aging category. In determining these percentages, the Company evaluates historical write-offs, and current trends in customer credit quality, as well as changes in credit policies. At September 30, 2020, Ingram Micro, Inc. and Synnex Corporation accounted for 14.1% and 11.4% of the Company’s accounts receivable, respectively. At September 30, 2019, Synnex Corporation, Ingram Micro, Inc. and Carahsoft Technology accounted for 12.9%, 12.4% and 11.5% of the Company’s accounts receivable, respectively. No other customers accounted for more than 10% of total receivables as of September 30, 2020 and 2019. 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 24, 2020, the Company completed its acquisition of Shape Security, Inc. for a total purchase price of $1.0 billion, of which approximately $120.0 million of finite-lived developed technology was recorded. Management valued the developed technology using the multi-period excess earnings 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 respects to the revenue growth rate and technology migration curve. 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 2020, 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, 2020 and noted no indicators of impairment. Intangible Assets Intangible assets with finite lives consist of acquired developed technologies, 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. 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. 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 enterprise license arrangements, with non-standard terms and conditions. Management exercises significant judgment in assessing contractual terms in these arrangements to identify and evaluate performance obligations and total consideration. 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. Shipping and Handling 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. 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. Accrued warranty costs as of September 30, 2020 and 2019 were not material. 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 $7.8 million, $4.7 million and $4.6 million in advertising costs during the fiscal years 2020, 2019 and 2018, 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, 2020, 2019 and 2018. 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 four 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 life 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. For the fiscal 2018, 2019 and 2020 performance stock awards, the Company's Compensation Committee adopted a new set of metrics 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 May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) (ASU 2014-09). ASU 2014-09 and the related amendments outline a new, single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. The new model requires revenue recognition to depict the transfer of promised goods or services to customers in an amount that reflects the consideration a company expects to receive in exchange for those goods or services. The Company adopted this new accounting standard and the related amendments on October 1, 2018 using the modified retrospective method. Refer to Note 2 - Revenue from Contracts with Customers for further discussion. In February 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-02, Leases (Topic 842) (ASU 2016-02), which requires lessees to recognize on the balance sheet a right-of-use asset, representing its right to use the underlying asset for the lease term, and a corresponding lease liability for all leases with terms greater than twelve months. The Company's leases consist primarily of operating leases for its offices and lab spaces. The Company does not have finance leases. The guidance also requires qualitative and quantitative disclosures designed to assess the amount, timing and uncertainty of cash flows arising from leases. The Company adopted this standard on October 1, 2019 on a modified retrospective basis by applying the new standard to its lease portfolio as of October 1, 2019. Under the modified retrospective method, financial results reported in periods prior to fiscal 2020 are unchanged. As a result of the adoption of this standard, the Company recognized lease liabilities and corresponding right-of-use assets for its long-term leases for office space, which had a material impact on its consolidated balance sheets. The adoption of this standard had no impact on the consolidated income statements and consolidated statements of cash flows. Refer to Note 8 - Leases for further discussion. Upon adoption of the standard, the Company elected the package of three practical expedients for existing and expired contracts to not reassess: the existence of additional leases, lease classification, or the treatment of initial direct costs. The Company also applies the short-term lease exemption for leases with an original expected term of 12 months or less and expenses such leases month-to-month and does not record a right-of-use asset or lease liability. Short-term lease activity under the exception is not significant. Additionally, the Company does not separate lease and non-lease components in the allocation of minimum lease payments for its office space and equipment leases, as such separation is not significant. The Company includes in minimum lease payments, fixed and variable payments based on a rate or index, but excludes variable payments based on satisfying future benchmarks or actual future costs incurred; such amounts are expensed as incurred. To calculate the net present value, the Company applied an incremental borrowing rate. This incremental borrowing rate is determined using a portfolio approach based on the rate of interest the Company would pay to borrow an amount equal to the lease payments on a collateralized basis over a similar term. Renewal options to extend lease terms are excluded from the minimum lease term at lease commencement. Recently Issued Accounting Pronouncements 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 new standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted. The Company does not anticipate that the adoption of this standard will have a material impact on its consolidated financial statements. 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 new standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted. The Company does not anticipate that the adoption of this standard will hav

Revenue from Contracts with Cus

Revenue from Contracts with Customers	12 Months Ended
	Sep. 30, 2020
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, 2020 and 2019 (in thousands): 2020 2019 Balance, beginning of year $ 59,446 $ — Impacts from adoption of ASC 606 — 54,608 Additional capitalized contract acquisition costs deferred 43,557 33,925 Amortization of capitalized contract acquisition costs (32,607) (29,087) Balance, end of year $ 70,396 $ 59,446 Amortization of capitalized contract acquisition costs was $32.6 million and $29.1 million for the years ended September 30, 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. The Company records assets for amounts related to performance obligations that are satisfied but not yet billed and/or collected, in addition to contracts that have started, but not yet been fully billed. These assets are recorded as contract assets rather than receivables when receipt of the consideration is conditional on something other than the passage of time. 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 contract assets (current and noncurrent) for the years ended September 30, 2020 and 2019 (in thousands): 2020 2019 Balance, beginning of year $ 132,492 $ — Impacts from adoption of ASC 606 — 57,499 Revenue recognized during period but not yet billed 37,260 27,459 Contract asset net additions 123,533 88,068 Contract assets acquired through the purchase of Shape 6,045 — Contract assets reclassified to accounts receivable (98,858) (40,534) Balance, end of year $ 200,472 $ 132,492 As of September 30, 2020, contract assets that are expected to be reclassified to receivables 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. There were no impairments of contract assets during the year ended September 30, 2020. The table below shows significant movements in the deferred revenue balances (current and noncurrent) for the year ended September 30, 2020 and 2019 (in thousands): 2020 2019 Balance, beginning of year $ 1,198,116 $ 1,015,321 Impacts from adoption of ASC 606 — 68,078 Amounts billed but not recognized as revenues 850,022 866,142 Amounts acquired through the purchase of Shape 39,000 — Revenues recognized related to the opening balance of deferred revenue (814,506) (751,425) Balance, end of year $ 1,272,632 $ 1,198,116 The Company's contract assets and liabilities are reported in a net position on a contract by contract basis at the end of each reporting period. 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, 2020, the total non-cancelable remaining performance obligations under the Company's contracts with customers was approximately $1.3 billion and the Company expects to recognize revenues on approximately 69.4% of these remaining performance obligations over the next 12 months, 19.0% 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, 2020
Business Combinations [Abstract]
Business Combinations	Business Combinations Fiscal Year 2020 Acquisition of Shape Security, Inc. On December 19, 2019, the Company entered into a Merger Agreement (the "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. Pursuant to the 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 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 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 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 $ 53,934 Fair value of tangible assets: Accounts receivable 21,077 Deferred tax assets 24,619 Operating lease right-of-use assets 29,644 Other tangible assets 22,571 Identifiable intangible assets: Developed technologies 120,000 7 years Customer relationships 21,000 4 years Trade name 9,500 5 years Goodwill 799,611 Total assets acquired $ 1,101,956 Liabilities assumed Deferred revenue $ (39,000) Operating lease liabilities (30,773) Other assumed liabilities (18,571) Total liabilities assumed $ (88,344) Net assets acquired $ 1,013,612 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 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 considered material to the Company's operations. Fiscal Year 2019 Acquisition of Nginx, Inc. On March 9, 2019, the Company entered into a Merger Agreement (the "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 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 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 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 based on the estimated fair values 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 technologies 62,500 7 years Customer relationships 12,000 15 years Trade name 14,500 7 years Non-competition agreements 300 2 years Goodwill 503,414 Total assets acquired $ 646,324 Liabilities assumed Other assumed liabilities $ (9,116) Total liabilities assumed $ (9,116) Net assets acquired $ 637,208 The measurement period for the NGINX acquisition lapsed during the third quarter of fiscal 2020. The Company reduced the carrying amount of goodwill by $6.0 million to reflect an adjustment to consideration exchanged for the purchase of NGINX within the post-close measurement period. No other financial statement amounts were affected by this adjustment. The adjustment was not material to the current period or any of the previous period financial statements. 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. Tax deductible goodwill based on the Company's preliminary calculation is $490.3 million. Since the NGINX acquisition was completed on May 8, 2019, the F5 and NGINX teams have been executing a plan to integrate ongoing operations.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Sep. 30, 2020
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. 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’s financial assets measured at fair value on a recurring basis subject to the disclosure requirements at September 30, 2019, were as follows (in thousands): Fair Value Measurements at Reporting Date Using Fair Value at Quoted Prices in Significant Significant Cash equivalents $ 140,238 $ 153,404 $ — $ 293,642 Short-term investments Available-for-sale securities — certificates of deposit — 249 — 249 Available-for-sale securities — corporate bonds and notes — 259,547 — 259,547 Available-for-sale securities — municipal bonds and notes — 12,129 — 12,129 Available-for-sale securities — U.S. government securities — 78,992 — 78,992 Available-for-sale securities — U.S. government agency securities — 22,146 — 22,146 Long-term investments Available-for-sale securities — corporate bonds and notes — 298,916 — 298,916 Available-for-sale securities — municipal bonds and notes — 2,524 — 2,524 Available-for-sale securities — U.S. government securities — 5,515 — 5,515 Available-for-sale securities — U.S. government agency securities — 51,447 — 51,447 Total $ 140,238 $ 884,869 $ — $ 1,025,107 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. 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 and intangible assets 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 long-lived assets for impairment whenever events or changes in circumstances indicate its carrying amount may not be recoverable. During the year ended September 30, 2020, the Company recorded impairment of a right-of-use asset of $9.7 million related to the exit of a leased facility, which was allocated to various expense line items on the Company’s consolidated income statement. 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. No impairment of long-lived assets was noted as of and for the year ended 2018.

Short-Term And Long-Term Invest

Short-Term And Long-Term Investments	12 Months Ended
	Sep. 30, 2020
Investments [Abstract]
Short-Term And Long-Term Investments	Short-Term and Long-Term Investments Short-term investments consist of the following (in thousands): 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 September 30, 2019 Cost or Gross Gross Fair Value Certificates of deposit $ 249 $ — $ — $ 249 Corporate bonds and notes 259,242 402 (97) 259,547 Municipal bonds and notes 12,128 6 (5) 12,129 U.S. government securities 78,988 18 (14) 78,992 U.S. government agency securities 22,138 9 (1) 22,146 $ 372,745 $ 435 $ (117) $ 373,063 Long-term investments consist of the following (in thousands): 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 September 30, 2019 Cost or Gross Gross Fair Value Corporate bonds and notes $ 298,888 $ 469 $ (441) $ 298,916 Municipal bonds and notes 2,528 2 (6) 2,524 U.S. government securities 5,515 3 (3) 5,515 U.S. government agency securities 51,463 5 (21) 51,447 $ 358,394 $ 479 $ (471) $ 358,402 Interest income from investments was $12.2 million, $25.3 million and $17.0 million for fiscal years 2020, 2019 and 2018, respectively. Interest income is included in other 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, 2020 (in thousands): Less Than 12 Months 12 Months or Greater Total September 30, 2020 Fair Value Gross Fair 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 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, 2019 (in thousands): Less Than 12 Months 12 Months or Greater Total September 30, 2019 Fair Value Gross Fair Value Gross Fair Value Gross Corporate bonds and notes $ 237,747 $ (434) $ 109,613 $ (104) $ 347,360 $ (538) Municipal bonds and notes 864 — 7,800 (11) 8,664 (11) U.S. government securities 27,095 (12) 9,991 (5) 37,086 (17) U.S. government agency securities 30,946 (22) — — 30,946 (22) Total $ 296,652 $ (468) $ 127,404 $ (120) $ 424,056 $ (588) The Company invests in securities that are rated investment grade. The unrealized losses on investments for fiscal year 2020 were primarily caused by interest rate increases. The Company reviews the individual securities in its portfolio to determine whether a decline in a security's fair value below the amortized cost basis is other-than-temporary. The Company determined that as of September 30, 2020, there were no investments in its portfolio that were other-than-temporarily impaired.

Balance Sheet Details

Balance Sheet Details	12 Months Ended
	Sep. 30, 2020
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, 2020 2019 Cash and cash equivalents $ 849,556 $ 599,219 Restricted cash included in other assets, net 3,270 3,035 Total cash, cash equivalents and restricted cash $ 852,826 $ 602,254 Inventories Inventories consist of the following (in thousands): September 30, 2020 2019 Finished goods $ 17,096 $ 22,441 Raw materials 10,802 11,960 $ 27,898 $ 34,401 Other Current Assets Other current assets consist of the following (in thousands): September 30, 2020 2019 Contract assets $ 138,096 $ 79,407 Prepaid expenses 47,197 49,051 Capitalized contract acquisition costs 29,650 28,228 Other 44,563 26,188 $ 259,506 $ 182,874 Property and Equipment Property and equipment consist of the following (in thousands): September 30, 2020 2019 Computer equipment $ 153,256 $ 142,372 Software 95,288 85,866 Office furniture and equipment 45,280 38,892 Leasehold improvements 175,593 151,055 469,417 418,185 Accumulated depreciation and amortization (240,178) (194,759) $ 229,239 $ 223,426 Depreciation and amortization expense totaled approximately $59.5 million, $58.0 million, and $45.9 million for the fiscal years ended September 30, 2020, 2019 and 2018, respectively. During the year ended September 30, 2019, the Company recorded impairment of capitalized internal-use software costs of $6.3 million. The charge was reflected in the general and administrative expense line item on the Company’s consolidated statement of operations. Goodwill Changes in the carrying amount of goodwill during fiscal years 2020 and 2019 are summarized as follows (in thousands): Balance, September 30, 2018 $ 555,965 Acquisition of Nginx, Inc. 509,414 Balance, September 30, 2019 1,065,379 Acquisition of Shape Security, Inc. 799,611 Adjustment to goodwill 1 (6,024) Balance, September 30, 2020 $ 1,858,966 (1) The Company reduced the carrying amount of goodwill by $6.0 million in the third quarter of fiscal year 2020 to reflect an adjustment to consideration exchanged for the purchase of NGINX within the post-close measurement period. Other Assets Other assets consist of the following (in thousands): September 30, 2020 2019 Intangible assets $ 225,900 $ 108,903 Contract assets 62,377 53,085 Capitalized contract acquisition costs 40,746 31,218 Other 18,424 10,575 $ 347,447 $ 203,781 Intangible assets are included in other assets on the balance sheet and consist of the following (in thousands): 2020 2019 Gross Accumulated Net Carrying Gross Accumulated Net Carrying Developed technology $ 246,173 $ (76,556) $ 169,617 $ 126,173 $ (53,213) $ 72,960 Customer relationships 41,242 (10,657) 30,585 20,242 (5,533) 14,709 Patents and trademarks 20,260 (14,448) 5,812 19,160 (11,800) 7,360 Trade names 24,973 (5,174) 19,799 15,473 (1,836) 13,637 Non-compete covenants 2,260 (2,173) 87 2,260 (2,023) 237 $ 334,908 $ (109,008) $ 225,900 $ 183,308 $ (74,405) $ 108,903 Amortization expense related to intangible assets was approximately $34.6 million, $11.8 million, and $11.1 million for the fiscal years ended September 30, 2020, 2019 and 2018, respectively. Estimated amortization expense for intangible assets for the five succeeding fiscal years is as follows (in thousands): 2021 $ 42,722 2022 41,429 2023 40,625 2024 35,360 2025 29,624 $ 189,760 Accrued Liabilities Accrued liabilities consist of the following (in thousands): September 30, 2020 2019 Payroll and benefits $ 169,708 $ 138,453 Operating lease liabilities, current 46,010 — Income and other tax accruals 33,048 31,801 Other 72,632 65,615 $ 321,398 $ 235,869 Other Long-term Liabilities Other long-term liabilities consist of the following (in thousands): September 30, 2020 2019 Deferred rent $ — $ 66,103 Income taxes payable 49,846 42,324 Other 9,665 23,426 $ 59,511 $ 131,853

Debt Facilities

Debt Facilities	12 Months Ended
	Sep. 30, 2020
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, 2020, 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, 2020, the Company was in compliance with all covenants. As of September 30, 2020, $390.0 million of principal amount under the Term Loan Facility was outstanding, excluding unamortized debt issuance costs of $1.7 million. The weighted average interest rate on the principal amount under the Term Loan Facility outstanding balance was 2.365% for the period ending September 30, 2020. The following table presents the scheduled principal maturities as of September 30, 2020 (in thousands): Fiscal Years Ending September 30: 2021 $ 20,000 2022 20,000 2023 350,000 Total $ 390,000 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 2020 were not material.

Leases

Leases	12 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Leases	Leases During the first quarter of fiscal 2020, the Company adopted ASU 2016-02, Leases (Topic 842) (the "Leasing Standard") 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 has concluded that the renewal option is not yet likely to be exercised. 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 year ended September 30, 2020 were as follows (in thousands): Fiscal year ended September 30, 2020 Operating lease expense $ 49,925 Short-term lease expense 3,563 Variable lease expense 21,980 Total lease expense $ 75,468 In the fourth quarter of fiscal 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. Variable lease expense primarily consists of common area maintenance and parking expenses. The Company executed two sublease contracts that commenced during the first quarter of fiscal year 2020. Lease income payments commenced in the second fiscal quarter. The Company has three additional subleases through the fiscal 2020 acquisition of Shape Security. Supplemental balance sheet information related to the Company's operating leases was as follows (in thousands, except lease term and discount rate): September 30, 2020 Operating lease right-of-use assets, net $ 300,680 Operating lease liabilities, current 1 46,010 Operating lease liabilities, long-term 338,715 Total operating lease liabilities $ 384,725 Weighted average remaining lease term (in years) 10.2 Weighted average discount rate 2.58 % (1) Current portion of operating lease liabilities is included in accrued liabilities on the Company's consolidated balance sheet. As of September 30, 2020, 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 2021 $ 55,601 2022 56,813 2023 44,041 2024 39,590 2025 33,215 Thereafter 217,506 Total lease payments 446,766 Less: imputed interest (62,041) Total lease liabilities $ 384,725 Operating lease liabilities above do not include sublease income. As of September 30, 2020, the Company expects to receive sublease income of approximately $10.2 million, which consists of $4.5 million to be received in fiscal year 2021 and $5.7 million to be received over the two fiscal years thereafter. As of September 30, 2020, 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, 2020
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, 2020 2019 2018 United States $ 216,409 $ 360,648 $ 441,336 International 179,988 180,463 162,424 $ 396,397 $ 541,111 $ 603,760 The provision for income taxes consists of the following (in thousands): Years Ended September 30, 2020 2019 2018 Current U.S. federal $ 26,978 $ 43,039 $ 78,454 State 4,230 13,864 9,800 Foreign 50,368 49,197 41,040 Total 81,576 106,100 129,294 Deferred U.S. federal 10,875 8,716 21,259 State (1,121) 1,617 725 Foreign (2,374) (3,056) (1,207) Total 7,380 7,277 20,777 $ 88,956 $ 113,377 $ 150,071 The effective tax rate differs from the U.S. federal statutory rate as follows (in thousands): Years Ended September 30, 2020 2019 2018 Income tax provision at statutory rate $ 83,243 $ 113,633 $ 147,921 State taxes, net of federal benefit 4,258 14,206 9,349 Tax impact of foreign operations (7,693) (9,161) (6,696) Research and development and other credits (11,843) (12,760) (13,159) Domestic manufacturing deduction — — (9,722) Stock-based and other compensation 18,002 6,771 (150) Transition impacts of the Tax Cuts and Jobs Act — — 21,015 Other 2,989 688 1,513 $ 88,956 $ 113,377 $ 150,071 The provision for income taxes for fiscal year 2020, 2019, and 2018 includes various impacts from the Tax Cuts and Jobs Act enacted on December 22, 2017. Significant impacts for fiscal year 2020 include a deduction for foreign derived intangible income, a tax on global intangible low taxed income, and the base erosion anti-avoidance tax. Significant impacts for fiscal year 2019 include a reduction of the U.S. federal income tax rate to 21%, a deduction for foreign derived intangible income, a tax on global intangible low taxed income, and repeal of the deduction for income attributable to domestic production activities. Significant impacts for fiscal year 2018 include a reduction of the U.S. federal income tax rate to 24.5%, a tax for deemed repatriation of undistributed foreign earnings, and an expense from the remeasurement of the Company's net deferred tax assets to reflect the change in the U.S. federal income tax rate when temporary differences are expected to reverse. 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. In April 2020, recent interpretations of a German law relating to withholding taxes on intellectual property rights emerged. We have evaluated this law and do not expect a material impact to our financial position or results of operations. The Company benefits from tax incentive arrangements in certain foreign jurisdictions, which expire in fiscal year 2021 to 2034. The tax incentive agreements are conditional upon meeting certain operational, employment, and investment requirements. These arrangements decreased foreign taxes by $8.2 million, $8.1 million and $6.4 million, and increased diluted earnings per common share by $0.13, $0.13 and $0.10 for the years ended September 30, 2020, 2019 and 2018, 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, 2020 2019 Deferred tax assets Net operating loss carry-forwards $ 54,842 $ 12,269 Accrued compensation and benefits 13,162 13,478 Stock-based compensation 13,010 7,144 Deferred revenue 40,577 35,247 Lease liabilities 19,656 17,313 Other accruals and reserves 17,384 15,786 Tax credit carryforwards 15,807 13,783 Depreciation 620 592 175,058 115,612 Valuation allowance (32,587) (23,495) 142,471 92,117 Deferred tax liabilities Purchased intangibles (46,491) (10,560) Depreciation (34,757) (39,910) Deferred costs (11,924) (10,656) Other accruals and reserves (4,728) (3,603) (97,900) (64,729) Net deferred tax assets $ 44,571 $ 27,388 At September 30, 2020, the Company had foreign net operating loss carryforwards of approximately $59.5 million that can be carried forward indefinitely, and $3.4 million that will expire in fiscal years 2026 to 2030. The Company had $170.7 million of federal net operating loss carryforwards, of which $111.8 million can be carried forward indefinitely and $58.9 million that will expire in fiscal years 2032 to 2037. The annual utilization of the federal net operating loss carryforwards is limited under Internal Revenue Code Section 382. The Company also had $379.6 million of state net operating loss carryforwards, of which $158.2 million can be carried forward indefinitely and $221.4 million will expire in fiscal years 2027 to 2040. In addition, there are $4.0 million of foreign credit carryforwards that will expire in fiscal years 2021 to 2036, $0.5 million of federal credit carryforwards that will expire in fiscal year 2039, $15.6 million of state tax credit carryforwards that can be carried forward indefinitely, and $3.7 million of state tax credit carryforwards that will expire in fiscal years 2030 to 2035. 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 $9.1 million and $0.7 million for years ended September 30, 2020 and 2019, 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 2020, 2019 and 2018 (in thousands): 2020 2019 2018 Balance, beginning of period $ 42,287 $ 31,672 $ 23,135 Gross increases related to prior period tax positions 8,664 5,129 2,715 Gross decreases related to prior period tax positions (1,051) (287) — Gross increases related to current period tax positions 9,272 7,756 8,230 Decreases relating to settlements with tax authorities (3,578) — — Reductions due to lapses of statute of limitations (3,827) (1,983) (2,408) Balance, end of period $ 51,767 $ 42,287 $ 31,672 The total amount of gross unrecognized tax benefits was $51.8 million, $42.3 million, and $31.7 million as of September 30, 2020, 2019, and 2018, respectively, of which, $34.3 million, $29.4 million, and $23.1 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, 2020, 2019 and 2018, the Company recorded approximately $1.0 million decrease, $2.4 million increase and $0.4 million increase, respectively, of interest and penalty expense related to uncertain tax positions. As of September 30, 2020 and 2019, the Company had a cumulative balance of accrued interest and penalties on unrecognized tax positions of $3.0 million and $4.0 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, 2016. Major jurisdictions where there are wholly owned subsidiaries of F5 Networks, Inc. which require income tax filings include the United Kingdom, Japan, Singapore, Australia, and Israel. The earliest periods open for review by local taxing authorities are fiscal years 2019 for the United Kingdom, 2014 for Japan, 2015 for Singapore, 2016 for Australia, and 2013 for Israel. The Company is currently under audit by various states for fiscal years 2015 through 2018 and by Israel for fiscal years 2013 to 2017. Within the next four fiscal quarters, the statute of limitations will begin to close on the fiscal year 2017 federal income tax return, fiscal years 2015, 2016, and 2017 state income tax returns and fiscal years 2013 to 2019 foreign income tax returns.

Shareholders' Equity

Shareholders' Equity	12 Months Ended
	Sep. 30, 2020
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 new authorization is incremental to the existing $4.4 billion program, initially approved in October 2010 and expanded in each fiscal year. Acquisitions for the share repurchase programs will be made from time to time in private transactions or open market purchases as permitted by securities laws and other legal requirements. The programs can be terminated at any time. During fiscal year 2020, the Company repurchased and retired 799,495 shares at an average price of $125.10 per share and as of September 30, 2020, the Company had $1.3 billion remaining authorized to purchase shares. Shares repurchased and retired during the fourth quarter of fiscal year 2020 are as follows (in thousands, except shares and per share data): Total Number of Shares Purchased 1 Average Price Total Number of Approximate Dollar Value of Shares that May Yet be Purchased Under the Plan 2 July 1, 2020 — July 31, 2020 — $ — — $ 1,322,518 August 1, 2020 — August 31, 2020 373,078 $ 139.79 357,644 $ 1,272,511 September 1, 2020 — September 30, 2020 — $ — — $ 1,272,511 (1) Includes 15,434 shares withheld from restricted stock units that vested in the fourth quarter of 2020 to satisfy minimum tax withholding obligations that arose on the vesting of restricted stock units. (2) Shares withheld from restricted stock units that vested to satisfy minimum tax withholding obligations that arose on the vesting of such awards do not deplete the dollar amount available for purchases under the repurchase program.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Sep. 30, 2020
Share-based Payment Arrangement, Noncash Expense [Abstract]
Stock-Based Compensation	Stock-based Compensation The Company recognized $201.9 million, $162.9 million and $157.9 million of stock-based compensation expense for the fiscal years ended September 30, 2020, 2019 and 2018, respectively. The income tax benefit recognized on stock-based compensation within income tax expense was $37.6 million, $31.3 million and $34.6 million for the fiscal years ended September 30, 2020, 2019 and 2018, respectively. As of September 30, 2020, there was $205.6 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 30, 2020, the Company’s Board of Directors and Compensation Committee approved 1,451,566 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, 2020 there were 1,899,745 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 2020 2019 2018 Risk-free interest rate 1.10% - 1.97% 2.25% - 2.51% 1.14% - 1.77% Expected dividend — — — Expected term 0.5 years 0.5 years 0.5 years Expected volatility 26.32% - 41.94% 18.14% - 31.74% 22.03% - 24.87% 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 2020, the Company issued no stock options or restricted stock units under the Traffix Plan. As of September 30, 2020, 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 2020, the Company issued no stock options or restricted stock units under the Nginx Acquisition Plan. As of September 30, 2020, there were no options outstanding and 121,820 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 2020, the Company issued no stock options or restricted stock units under the Nginx Plan. As of September 30, 2020, there were options to purchase 131,342 shares outstanding and 17,986 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 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 2020, the Company issued no stock options and 411,385 restricted stock units under the Shape Acquisition Plan. As of September 30, 2020, there were no options outstanding and 377,066 stock units outstanding. 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 2020, the Company issued (including conversions to Company awards) 334,709 stock options and 7,703 stock units under the Shape Plan. As of September 30, 2020, there were options to purchase 259,709 shares outstanding and 5,631 stock units outstanding. 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 21,280,000 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 2020, the Company issued no stock options, 152,199 performance stock units and 1,237,609 restricted stock units under the 2014 Plan. As of September 30, 2020, there were no options outstanding, 145,869 performance stock units outstanding, 1,204,290 restricted stock units outstanding and 2,453,277 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, 2019 55,184 $ 165.83 1,041,889 $ 158.10 Units granted 152,199 147.30 1,237,609 142.58 Units vested (42,053) 142.01 (933,413) 134.49 Units cancelled (19,461) 157.81 (141,795) 150.58 Balance, September 30, 2020 145,869 $ 146.42 1,204,290 $ 146.39 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 Networks Members Dividend November 1, 2019 Tranche 1 $ 196.02 0.91 1.53 % 27.61 % 26.88 % — Tranche 2 $ 199.85 1.91 1.55 % 26.22 % 26.70 % — Tranche 3 $ 202.56 2.91 1.54 % 24.90 % 24.82 % — As of September 30, 2020, 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 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 November 1, 2016 115,347 Quarterly 4 years November 1, 2020 (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, 2019 207,759 $ 24.43 Options granted 334,709 41.10 Options exercised (104,487) 24.84 Options cancelled (46,881) 40.09 Balance, September 30, 2020 391,100 $ 36.71 All stock options granted in fiscal year 2020 and 2019 were replacement awards of those assumed as part of the acquisitions of Shape and NGINX, respectively. No stock options were granted in fiscal year 2018. The total intrinsic value of options exercised during fiscal 2020, 2019 and 2018 was $11.4 million, $0.7 million and $0.1 million, respectively. A summary of options outstanding that are exercisable and that have vested and are expected to vest as of September 30, 2020 is as follows: Number of Weighted Weighted Aggregate (In thousands) Stock options outstanding 391,100 7.81 $ 36.71 $ 34,236 Exercisable 119,734 7.11 $ 25.38 $ 11,683 Vested and expected to vest 368,503 7.77 $ 36.04 $ 32,477 (1) Aggregate intrinsic value represents the difference between the fair value of the Company’s common stock underlying these options at September 30, 2020 and the related exercise prices. As of September 30, 2020, equity based awards (including stock options and restricted stock units) are available for future issuance as follows: Awards Balance, September 30, 2019 2,939,974 Granted (2,143,605) Cancelled 266,925 Additional shares reserved (terminated), net 1,651,664 Balance, September 30, 2020 2,714,958

Net Income Per Share

Net Income Per Share	12 Months Ended
	Sep. 30, 2020
Net Income Per Share [Abstract]
Net Income Per Share	Net Income Per Share Basic net income per share is computed by dividing net income by the weighted average number of 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, 2020 2019 2018 Numerator Net income $ 307,441 $ 427,734 $ 453,689 Denominator Weighted average shares outstanding — basic 60,911 60,044 61,262 Dilutive effect of common shares from stock options and restricted stock units 467 412 751 Weighted average shares outstanding — diluted 61,378 60,456 62,013 Basic net income per share $ 5.05 $ 7.12 $ 7.41 Diluted net income per share $ 5.01 $ 7.08 $ 7.32 Anti-dilutive stock-based awards excluded from the calculations of diluted earnings per share were immaterial for the years ended September 30, 2020, 2019 and 2018.

Commitments And Contingencies

Commitments And Contingencies	12 Months Ended
	Sep. 30, 2020
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, 2020, the Company’s remaining unfulfilled purchase obligations were $18.1 million. Litigation 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. The Company and the other defendants have filed motions to dismiss all claims asserted against them in the lawsuit. In addition to the above matter, 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 an accrual for loss contingencies associated with the legal proceedings or the investigations discussed above.

Restructuring Charges

Restructuring Charges	12 Months Ended
	Sep. 30, 2020
Restructuring and Related Activities [Abstract]
Restructuring Charges	Restructuring Charges In 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 significant future charges related to the restructuring plan. During fiscal year 2020, the following activity was recorded (in thousands): Employee Severance, Benefits and Related Costs Accrued expenses, October 1, 2019 $ — Restructuring charges 7,800 Cash payments (7,639) Non-cash items — Accrued expenses, September 30, 2020 $ 161 In July 2018, the Company initiated a restructuring plan, which included a reduction in force program affecting approximately 215 employees. The Company recorded a restructuring charge of $18.4 million in the fourth quarter of fiscal 2018 and as of September 30, 2018, the Company had $8.3 million in accrued restructuring costs related to this plan. All severance restructuring costs had been paid as of September 30, 2019 and the plan was complete.

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Sep. 30, 2020
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, 2020, 2019, and 2018 were approximately $11.3 million, $10.5 million and $10.5 million, respectively. Contributions made by the Company vest over four years.

Segment Information

Segment Information	12 Months Ended
	Sep. 30, 2020
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, 2020 2019 2018 Americas: United States $ 1,221,190 $ 1,137,556 $ 1,088,270 Other 95,878 108,112 116,073 Total Americas 1,317,068 1,245,668 1,204,343 EMEA 593,307 553,701 546,239 Asia Pacific 440,447 443,078 410,825 $ 2,350,822 $ 2,242,447 $ 2,161,407 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, 2020 2019 2018 Net product revenues Systems revenue $ 668,313 $ 745,798 $ 810,182 Software revenue 357,543 239,793 149,926 Total net product revenue $ 1,025,856 $ 985,591 $ 960,108 The following distributors of the Company's products accounted for more than 10% of total net revenue: Years Ended September 30, 2020 2019 2018 Ingram Micro, Inc. 16.7 % 18.2 % 16.6 % Tech Data — 10.2 % 11.6 % Westcon Group, Inc. — 10.0 % 10.4 % Synnex Corporation — — 10.8 % Arrow ECS — — 10.7 % The Company tracks assets by physical location. Long-lived assets consist of property and equipment, net, and are shown below (in thousands): September 30, 2020 2019 United States $ 190,509 $ 194,176 EMEA 20,361 13,451 Other countries 18,369 15,799 $ 229,239 $ 223,426

Quarterly Results Of Operations

Quarterly Results Of Operations (Unaudited)	12 Months Ended
	Sep. 30, 2020
Quarterly Financial Data [Abstract]
Quarterly Results Of Operations (Unaudited)	Quarterly Results of Operations (Unaudited) The following presents the Company’s unaudited quarterly results of operations for the eight quarters ended September 30, 2020. The information should be read in conjunction with the Company’s financial statements and related notes included elsewhere in this report. This unaudited information has been prepared on the same basis as the audited financial statements and includes all adjustments, consisting only of normal recurring adjustments that were considered necessary for a fair statement of the Company’s operating results for the quarters presented. Three Months Ended Sept. 30, 2020 June 30, 2020 March 31, 2020 Dec. 31, 2019 Sept. 30, 2019 June 30, 2019 March 31, 2019 Dec. 31, 2018 (unaudited and in thousands, except per share data) Net revenues Products $ 278,451 $ 253,331 $ 259,538 $ 234,536 $ 264,926 $ 248,929 $ 237,859 $ 233,877 Services 336,365 329,921 323,911 334,769 325,462 314,465 307,036 309,893 Total 614,816 583,252 583,449 569,305 590,388 563,394 544,895 543,770 Cost of net revenues Products 62,634 57,437 53,086 42,118 44,693 44,336 43,547 42,410 Services 49,333 48,603 48,152 46,524 46,225 46,431 44,631 44,304 Total 111,967 106,040 101,238 88,642 90,918 90,767 88,178 86,714 Gross profit 502,849 477,212 482,211 480,663 499,470 472,627 456,717 457,056 Operating expenses Sales and marketing 220,379 211,808 215,472 195,519 217,554 195,852 170,954 164,259 Research and development 120,300 115,991 109,028 96,005 102,812 116,894 96,314 92,038 General and administrative 63,557 61,792 74,013 59,004 64,390 57,141 46,656 42,543 Restructuring charges — — — 7,800 — — — — Total operating expenses 404,236 389,591 398,513 358,328 384,756 369,887 313,924 298,840 Income from operations 98,613 87,621 83,698 122,335 114,714 102,740 142,793 158,216 Other income, net (1,090) 141 (141) 5,220 3,397 4,722 7,434 7,095 Income before income taxes 97,523 87,762 83,557 127,555 118,111 107,462 150,227 165,311 Provision for income taxes 19,860 17,890 22,178 29,028 23,274 21,557 34,140 34,406 Net income $ 77,663 $ 69,872 $ 61,379 $ 98,527 $ 94,837 $ 85,905 $ 116,087 $ 130,905 Net income per share — basic $ 1.27 $ 1.15 $ 1.01 $ 1.62 $ 1.57 $ 1.43 $ 1.94 $ 2.17 Weighted average shares — basic 61,149 60,978 60,869 60,649 60,283 59,981 59,686 60,216 Net income per share — diluted $ 1.26 $ 1.14 $ 1.00 $ 1.62 $ 1.57 $ 1.43 $ 1.93 $ 2.16 Weighted average shares — diluted 61,636 61,415 61,084 60,815 60,448 60,196 60,029 60,645

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policy)	12 Months Ended
	Sep. 30, 2020
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.
Prior Period Reclassifications	Prior Period Reclassifications Certain prior year amounts have been reclassified to conform to the current year presentation in the Consolidated Statements of Cash Flows. The reclassified amounts are considered immaterial and there was no change to total cash from operating, investing or financing activities as a result.
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 and outcomes may differ from management's estimates and assumptions. In December 2019, a novel strain of coronavirus (“COVID-19“) was first identified, and in March 2020, the World Health Organization categorized COVID-19 as a pandemic. The Company assessed the impact that COVID-19 had on its results of operations, including, but not limited to an assessment of its allowance for doubtful accounts, the carrying value of short-term and long-term investments, the carrying value of goodwill and other long-lived assets, and the impact to revenue recognition and cost of revenues. The Company is actively monitoring the impact to the results of its business operations, and may make decisions required by federal, state or local authorities, or that are determined to be in the best interests of its employees, customers, partners, suppliers and stockholders. As of the filing date, the extent to which the COVID-19 pandemic may impact the Company’s financial condition or results of operations remains uncertain.
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 declines in value of securities judged to be other than temporary are included in other income (expense). 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.
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 doubtful accounts is recorded to account for potential bad debts. Estimates are used in determining the allowance for doubtful accounts and are based upon an assessment of selected accounts and as a percentage of remaining accounts receivable by aging category. In determining these percentages, the Company evaluates historical write-offs, and current trends in customer credit quality, as well as changes in credit policies. At September 30, 2020, Ingram Micro, Inc. and Synnex Corporation accounted for 14.1% and 11.4% of the Company’s accounts receivable, respectively. At September 30, 2019, Synnex Corporation, Ingram Micro, Inc. and Carahsoft Technology accounted for 12.9%, 12.4% and 11.5% of the Company’s accounts receivable, respectively. No other customers accounted for more than 10% of total receivables as of September 30, 2020 and 2019. 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, 2020 2019 Computer equipment $ 153,256 $ 142,372 Software 95,288 85,866 Office furniture and equipment 45,280 38,892 Leasehold improvements 175,593 151,055 469,417 418,185 Accumulated depreciation and amortization (240,178) (194,759) $ 229,239 $ 223,426
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 24, 2020, the Company completed its acquisition of Shape Security, Inc. for a total purchase price of $1.0 billion, of which approximately $120.0 million of finite-lived developed technology was recorded. Management valued the developed technology using the multi-period excess earnings 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 respects to the revenue growth rate and technology migration curve.
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 2020, 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, 2020 and noted no indicators of impairment.
Intangible Assets	Intangible AssetsIntangible assets with finite lives consist of acquired developed technologies, 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. 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. 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 enterprise license arrangements, with non-standard terms and conditions. Management exercises significant judgment in assessing contractual terms in these arrangements to identify and evaluate performance obligations and total consideration. 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.
Shipping And Handling	Shipping and Handling 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.
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. Accrued warranty costs as of September 30, 2020 and 2019 were not material.
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 $7.8 million, $4.7 million and $4.6 million in advertising costs during the fiscal years 2020, 2019 and 2018, 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, 2020, 2019 and 2018.
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 four 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 life 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. For the fiscal 2018, 2019 and 2020 performance stock awards, the Company's Compensation Committee adopted a new set of metrics 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 May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606) (ASU 2014-09). ASU 2014-09 and the related amendments outline a new, single comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance, including industry-specific guidance. The new model requires revenue recognition to depict the transfer of promised goods or services to customers in an amount that reflects the consideration a company expects to receive in exchange for those goods or services. The Company adopted this new accounting standard and the related amendments on October 1, 2018 using the modified retrospective method. Refer to Note 2 - Revenue from Contracts with Customers for further discussion. In February 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-02, Leases (Topic 842) (ASU 2016-02), which requires lessees to recognize on the balance sheet a right-of-use asset, representing its right to use the underlying asset for the lease term, and a corresponding lease liability for all leases with terms greater than twelve months. The Company's leases consist primarily of operating leases for its offices and lab spaces. The Company does not have finance leases. The guidance also requires qualitative and quantitative disclosures designed to assess the amount, timing and uncertainty of cash flows arising from leases. The Company adopted this standard on October 1, 2019 on a modified retrospective basis by applying the new standard to its lease portfolio as of October 1, 2019. Under the modified retrospective method, financial results reported in periods prior to fiscal 2020 are unchanged. As a result of the adoption of this standard, the Company recognized lease liabilities and corresponding right-of-use assets for its long-term leases for office space, which had a material impact on its consolidated balance sheets. The adoption of this standard had no impact on the consolidated income statements and consolidated statements of cash flows. Refer to Note 8 - Leases for further discussion. Upon adoption of the standard, the Company elected the package of three practical expedients for existing and expired contracts to not reassess: the existence of additional leases, lease classification, or the treatment of initial direct costs. The Company also applies the short-term lease exemption for leases with an original expected term of 12 months or less and expenses such leases month-to-month and does not record a right-of-use asset or lease liability. Short-term lease activity under the exception is not significant. Additionally, the Company does not separate lease and non-lease components in the allocation of minimum lease payments for its office space and equipment leases, as such separation is not significant. The Company includes in minimum lease payments, fixed and variable payments based on a rate or index, but excludes variable payments based on satisfying future benchmarks or actual future costs incurred; such amounts are expensed as incurred. To calculate the net present value, the Company applied an incremental borrowing rate. This incremental borrowing rate is determined using a portfolio approach based on the rate of interest the Company would pay to borrow an amount equal to the lease payments on a collateralized basis over a similar term. Renewal options to extend lease terms are excluded from the minimum lease term at lease commencement. Recently Issued Accounting Pronouncements 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 new standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted. The Company does not anticipate that the adoption of this standard will have a material impact on its consolidated financial statements. 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 new standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. Early adoption is permitted. The Company does not anticipate that the adoption of this standard will have a material impact on its consolidated financial statements.

Accounting Policies (Tables)

Accounting Policies (Tables)	12 Months Ended
	Sep. 30, 2020
Accounting Policies [Abstract]
Schedule of Inventories	Inventories consist of the following (in thousands): September 30, 2020 2019 Finished goods $ 17,096 $ 22,441 Raw materials 10,802 11,960 $ 27,898 $ 34,401
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, 2020 2019 2018 Numerator Net income $ 307,441 $ 427,734 $ 453,689 Denominator Weighted average shares outstanding — basic 60,911 60,044 61,262 Dilutive effect of common shares from stock options and restricted stock units 467 412 751 Weighted average shares outstanding — diluted 61,378 60,456 62,013 Basic net income per share $ 5.05 $ 7.12 $ 7.41 Diluted net income per share $ 5.01 $ 7.08 $ 7.32

Revenue from Contracts with C_2

Revenue from Contracts with Customers (Tables)	12 Months Ended
	Sep. 30, 2020
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, 2020 and 2019 (in thousands): 2020 2019 Balance, beginning of year $ 59,446 $ — Impacts from adoption of ASC 606 — 54,608 Additional capitalized contract acquisition costs deferred 43,557 33,925 Amortization of capitalized contract acquisition costs (32,607) (29,087) Balance, end of year $ 70,396 $ 59,446
Contract with Customer, Asset and Liability	The table below shows significant movements in contract assets (current and noncurrent) for the years ended September 30, 2020 and 2019 (in thousands): 2020 2019 Balance, beginning of year $ 132,492 $ — Impacts from adoption of ASC 606 — 57,499 Revenue recognized during period but not yet billed 37,260 27,459 Contract asset net additions 123,533 88,068 Contract assets acquired through the purchase of Shape 6,045 — Contract assets reclassified to accounts receivable (98,858) (40,534) Balance, end of year $ 200,472 $ 132,492 2020 2019 Balance, beginning of year $ 1,198,116 $ 1,015,321 Impacts from adoption of ASC 606 — 68,078 Amounts billed but not recognized as revenues 850,022 866,142 Amounts acquired through the purchase of Shape 39,000 — Revenues recognized related to the opening balance of deferred revenue (814,506) (751,425) Balance, end of year $ 1,272,632 $ 1,198,116

Business Combinations (Tables)

Business Combinations (Tables)	12 Months Ended
	Sep. 30, 2020
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 $ 53,934 Fair value of tangible assets: Accounts receivable 21,077 Deferred tax assets 24,619 Operating lease right-of-use assets 29,644 Other tangible assets 22,571 Identifiable intangible assets: Developed technologies 120,000 7 years Customer relationships 21,000 4 years Trade name 9,500 5 years Goodwill 799,611 Total assets acquired $ 1,101,956 Liabilities assumed Deferred revenue $ (39,000) Operating lease liabilities (30,773) Other assumed liabilities (18,571) Total liabilities assumed $ (88,344) Net assets acquired $ 1,013,612 The allocated purchase consideration to assets acquired and liabilities assumed based on the estimated fair values 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 technologies 62,500 7 years Customer relationships 12,000 15 years Trade name 14,500 7 years Non-competition agreements 300 2 years Goodwill 503,414 Total assets acquired $ 646,324 Liabilities assumed Other assumed liabilities $ (9,116) Total liabilities assumed $ (9,116) Net assets acquired $ 637,208

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Sep. 30, 2020
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, 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’s financial assets measured at fair value on a recurring basis subject to the disclosure requirements at September 30, 2019, were as follows (in thousands): Fair Value Measurements at Reporting Date Using Fair Value at Quoted Prices in Significant Significant Cash equivalents $ 140,238 $ 153,404 $ — $ 293,642 Short-term investments Available-for-sale securities — certificates of deposit — 249 — 249 Available-for-sale securities — corporate bonds and notes — 259,547 — 259,547 Available-for-sale securities — municipal bonds and notes — 12,129 — 12,129 Available-for-sale securities — U.S. government securities — 78,992 — 78,992 Available-for-sale securities — U.S. government agency securities — 22,146 — 22,146 Long-term investments Available-for-sale securities — corporate bonds and notes — 298,916 — 298,916 Available-for-sale securities — municipal bonds and notes — 2,524 — 2,524 Available-for-sale securities — U.S. government securities — 5,515 — 5,515 Available-for-sale securities — U.S. government agency securities — 51,447 — 51,447 Total $ 140,238 $ 884,869 $ — $ 1,025,107

Short-Term And Long-Term Inve_2

Short-Term And Long-Term Investments (Tables)	12 Months Ended
	Sep. 30, 2020
Schedule of Investments [Line Items]
Schedule Of Short-Term And Long-Term Investments	Short-term investments consist of the following (in thousands): 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 September 30, 2019 Cost or Gross Gross Fair Value Certificates of deposit $ 249 $ — $ — $ 249 Corporate bonds and notes 259,242 402 (97) 259,547 Municipal bonds and notes 12,128 6 (5) 12,129 U.S. government securities 78,988 18 (14) 78,992 U.S. government agency securities 22,138 9 (1) 22,146 $ 372,745 $ 435 $ (117) $ 373,063 Long-term investments consist of the following (in thousands): 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 September 30, 2019 Cost or Gross Gross Fair Value Corporate bonds and notes $ 298,888 $ 469 $ (441) $ 298,916 Municipal bonds and notes 2,528 2 (6) 2,524 U.S. government securities 5,515 3 (3) 5,515 U.S. government agency securities 51,463 5 (21) 51,447 $ 358,394 $ 479 $ (471) $ 358,402
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, 2020 (in thousands): Less Than 12 Months 12 Months or Greater Total September 30, 2020 Fair Value Gross Fair 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 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, 2019 (in thousands): Less Than 12 Months 12 Months or Greater Total September 30, 2019 Fair Value Gross Fair Value Gross Fair Value Gross Corporate bonds and notes $ 237,747 $ (434) $ 109,613 $ (104) $ 347,360 $ (538) Municipal bonds and notes 864 — 7,800 (11) 8,664 (11) U.S. government securities 27,095 (12) 9,991 (5) 37,086 (17) U.S. government agency securities 30,946 (22) — — 30,946 (22) Total $ 296,652 $ (468) $ 127,404 $ (120) $ 424,056 $ (588)

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	12 Months Ended
	Sep. 30, 2020
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, 2020 2019 Cash and cash equivalents $ 849,556 $ 599,219 Restricted cash included in other assets, net 3,270 3,035 Total cash, cash equivalents and restricted cash $ 852,826 $ 602,254
Inventories	Inventories consist of the following (in thousands): September 30, 2020 2019 Finished goods $ 17,096 $ 22,441 Raw materials 10,802 11,960 $ 27,898 $ 34,401
Other Current Assets	Other current assets consist of the following (in thousands): September 30, 2020 2019 Contract assets $ 138,096 $ 79,407 Prepaid expenses 47,197 49,051 Capitalized contract acquisition costs 29,650 28,228 Other 44,563 26,188 $ 259,506 $ 182,874
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, 2020 2019 Computer equipment $ 153,256 $ 142,372 Software 95,288 85,866 Office furniture and equipment 45,280 38,892 Leasehold improvements 175,593 151,055 469,417 418,185 Accumulated depreciation and amortization (240,178) (194,759) $ 229,239 $ 223,426
Goodwill	Changes in the carrying amount of goodwill during fiscal years 2020 and 2019 are summarized as follows (in thousands): Balance, September 30, 2018 $ 555,965 Acquisition of Nginx, Inc. 509,414 Balance, September 30, 2019 1,065,379 Acquisition of Shape Security, Inc. 799,611 Adjustment to goodwill 1 (6,024) Balance, September 30, 2020 $ 1,858,966 (1) The Company reduced the carrying amount of goodwill by $6.0 million in the third quarter of fiscal year 2020 to reflect an adjustment to consideration exchanged for the purchase of NGINX within the post-close measurement period.
Other Assets	Other assets consist of the following (in thousands): September 30, 2020 2019 Intangible assets $ 225,900 $ 108,903 Contract assets 62,377 53,085 Capitalized contract acquisition costs 40,746 31,218 Other 18,424 10,575 $ 347,447 $ 203,781
Intangible Assets	Intangible assets are included in other assets on the balance sheet and consist of the following (in thousands): 2020 2019 Gross Accumulated Net Carrying Gross Accumulated Net Carrying Developed technology $ 246,173 $ (76,556) $ 169,617 $ 126,173 $ (53,213) $ 72,960 Customer relationships 41,242 (10,657) 30,585 20,242 (5,533) 14,709 Patents and trademarks 20,260 (14,448) 5,812 19,160 (11,800) 7,360 Trade names 24,973 (5,174) 19,799 15,473 (1,836) 13,637 Non-compete covenants 2,260 (2,173) 87 2,260 (2,023) 237 $ 334,908 $ (109,008) $ 225,900 $ 183,308 $ (74,405) $ 108,903
Estimated Amortization Expense For Intangible Assets	Estimated amortization expense for intangible assets for the five succeeding fiscal years is as follows (in thousands): 2021 $ 42,722 2022 41,429 2023 40,625 2024 35,360 2025 29,624 $ 189,760
Accrued Liabilities	Accrued liabilities consist of the following (in thousands): September 30, 2020 2019 Payroll and benefits $ 169,708 $ 138,453 Operating lease liabilities, current 46,010 — Income and other tax accruals 33,048 31,801 Other 72,632 65,615 $ 321,398 $ 235,869
Other Long-term Liabilities	Other long-term liabilities consist of the following (in thousands): September 30, 2020 2019 Deferred rent $ — $ 66,103 Income taxes payable 49,846 42,324 Other 9,665 23,426 $ 59,511 $ 131,853

Debt Facilities (Tables)

Debt Facilities (Tables)	12 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Schedule of Maturities of Long-term Debt	The following table presents the scheduled principal maturities as of September 30, 2020 (in thousands): Fiscal Years Ending September 30: 2021 $ 20,000 2022 20,000 2023 350,000 Total $ 390,000

Leases (Tables)

Leases (Tables)	12 Months Ended
	Sep. 30, 2020
Leases [Abstract]
Lease, Cost	The components of the Company's operating lease expenses for the year ended September 30, 2020 were as follows (in thousands): Fiscal year ended September 30, 2020 Operating lease expense $ 49,925 Short-term lease expense 3,563 Variable lease expense 21,980 Total lease expense $ 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, 2020 Operating lease right-of-use assets, net $ 300,680 Operating lease liabilities, current 1 46,010 Operating lease liabilities, long-term 338,715 Total operating lease liabilities $ 384,725 Weighted average remaining lease term (in years) 10.2 Weighted average discount rate 2.58 % (1) Current portion of operating lease liabilities is included in accrued liabilities on the Company's consolidated balance sheet.
Lessee, Operating Lease, Liability, Maturity	As of September 30, 2020, 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 2021 $ 55,601 2022 56,813 2023 44,041 2024 39,590 2025 33,215 Thereafter 217,506 Total lease payments 446,766 Less: imputed interest (62,041) Total lease liabilities $ 384,725
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, 2020
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, 2020 2019 2018 United States $ 216,409 $ 360,648 $ 441,336 International 179,988 180,463 162,424 $ 396,397 $ 541,111 $ 603,760
Schedule Of Provision For Income Taxes (Benefit)	The provision for income taxes consists of the following (in thousands): Years Ended September 30, 2020 2019 2018 Current U.S. federal $ 26,978 $ 43,039 $ 78,454 State 4,230 13,864 9,800 Foreign 50,368 49,197 41,040 Total 81,576 106,100 129,294 Deferred U.S. federal 10,875 8,716 21,259 State (1,121) 1,617 725 Foreign (2,374) (3,056) (1,207) Total 7,380 7,277 20,777 $ 88,956 $ 113,377 $ 150,071
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, 2020 2019 2018 Income tax provision at statutory rate $ 83,243 $ 113,633 $ 147,921 State taxes, net of federal benefit 4,258 14,206 9,349 Tax impact of foreign operations (7,693) (9,161) (6,696) Research and development and other credits (11,843) (12,760) (13,159) Domestic manufacturing deduction — — (9,722) Stock-based and other compensation 18,002 6,771 (150) Transition impacts of the Tax Cuts and Jobs Act — — 21,015 Other 2,989 688 1,513 $ 88,956 $ 113,377 $ 150,071
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, 2020 2019 Deferred tax assets Net operating loss carry-forwards $ 54,842 $ 12,269 Accrued compensation and benefits 13,162 13,478 Stock-based compensation 13,010 7,144 Deferred revenue 40,577 35,247 Lease liabilities 19,656 17,313 Other accruals and reserves 17,384 15,786 Tax credit carryforwards 15,807 13,783 Depreciation 620 592 175,058 115,612 Valuation allowance (32,587) (23,495) 142,471 92,117 Deferred tax liabilities Purchased intangibles (46,491) (10,560) Depreciation (34,757) (39,910) Deferred costs (11,924) (10,656) Other accruals and reserves (4,728) (3,603) (97,900) (64,729) Net deferred tax assets $ 44,571 $ 27,388
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 2020, 2019 and 2018 (in thousands): 2020 2019 2018 Balance, beginning of period $ 42,287 $ 31,672 $ 23,135 Gross increases related to prior period tax positions 8,664 5,129 2,715 Gross decreases related to prior period tax positions (1,051) (287) — Gross increases related to current period tax positions 9,272 7,756 8,230 Decreases relating to settlements with tax authorities (3,578) — — Reductions due to lapses of statute of limitations (3,827) (1,983) (2,408) Balance, end of period $ 51,767 $ 42,287 $ 31,672

Shareholders' Equity (Tables)

Shareholders' Equity (Tables)	3 Months Ended
	Sep. 30, 2020
Equity [Abstract]
Common Stock Repurchased and Retired	Shares repurchased and retired during the fourth quarter of fiscal year 2020 are as follows (in thousands, except shares and per share data): Total Number of Shares Purchased 1 Average Price Total Number of Approximate Dollar Value of Shares that May Yet be Purchased Under the Plan 2 July 1, 2020 — July 31, 2020 — $ — — $ 1,322,518 August 1, 2020 — August 31, 2020 373,078 $ 139.79 357,644 $ 1,272,511 September 1, 2020 — September 30, 2020 — $ — — $ 1,272,511 (1) Includes 15,434 shares withheld from restricted stock units that vested in the fourth quarter of 2020 to satisfy minimum tax withholding obligations that arose on the vesting of restricted stock units. (2) Shares withheld from restricted stock units that vested to satisfy minimum tax withholding obligations that arose on the vesting of such awards do not deplete the dollar amount available for purchases under the repurchase program.

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Sep. 30, 2020
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 2020 2019 2018 Risk-free interest rate 1.10% - 1.97% 2.25% - 2.51% 1.14% - 1.77% Expected dividend — — — Expected term 0.5 years 0.5 years 0.5 years Expected volatility 26.32% - 41.94% 18.14% - 31.74% 22.03% - 24.87%
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, 2019 55,184 $ 165.83 1,041,889 $ 158.10 Units granted 152,199 147.30 1,237,609 142.58 Units vested (42,053) 142.01 (933,413) 134.49 Units cancelled (19,461) 157.81 (141,795) 150.58 Balance, September 30, 2020 145,869 $ 146.42 1,204,290 $ 146.39
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 Networks Members Dividend November 1, 2019 Tranche 1 $ 196.02 0.91 1.53 % 27.61 % 26.88 % — Tranche 2 $ 199.85 1.91 1.55 % 26.22 % 26.70 % — Tranche 3 $ 202.56 2.91 1.54 % 24.90 % 24.82 % —
Schedule of Nonvested Restricted Stock Units Activity	As of September 30, 2020, 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 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 November 1, 2016 115,347 Quarterly 4 years November 1, 2020 (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, 2019 207,759 $ 24.43 Options granted 334,709 41.10 Options exercised (104,487) 24.84 Options cancelled (46,881) 40.09 Balance, September 30, 2020 391,100 $ 36.71
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, 2020 is as follows: Number of Weighted Weighted Aggregate (In thousands) Stock options outstanding 391,100 7.81 $ 36.71 $ 34,236 Exercisable 119,734 7.11 $ 25.38 $ 11,683 Vested and expected to vest 368,503 7.77 $ 36.04 $ 32,477 (1) Aggregate intrinsic value represents the difference between the fair value of the Company’s common stock underlying these options at September 30, 2020 and the related exercise prices.
Schedule Of Equity Based Awards (Including Stock Options And Restricted Stock Units)	As of September 30, 2020, equity based awards (including stock options and restricted stock units) are available for future issuance as follows: Awards Balance, September 30, 2019 2,939,974 Granted (2,143,605) Cancelled 266,925 Additional shares reserved (terminated), net 1,651,664 Balance, September 30, 2020 2,714,958

Net Income Per Share (Tables)

Net Income Per Share (Tables)	12 Months Ended
	Sep. 30, 2020
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, 2020 2019 2018 Numerator Net income $ 307,441 $ 427,734 $ 453,689 Denominator Weighted average shares outstanding — basic 60,911 60,044 61,262 Dilutive effect of common shares from stock options and restricted stock units 467 412 751 Weighted average shares outstanding — diluted 61,378 60,456 62,013 Basic net income per share $ 5.05 $ 7.12 $ 7.41 Diluted net income per share $ 5.01 $ 7.08 $ 7.32

Restructuring Charges (Tables)

Restructuring Charges (Tables)	12 Months Ended
	Sep. 30, 2020
Restructuring and Related Activities [Abstract]
Restructuring and Related Costs	During fiscal year 2020, the following activity was recorded (in thousands): Employee Severance, Benefits and Related Costs Accrued expenses, October 1, 2019 $ — Restructuring charges 7,800 Cash payments (7,639) Non-cash items — Accrued expenses, September 30, 2020 $ 161

Segment Information (Tables)

Segment Information (Tables)	12 Months Ended
	Sep. 30, 2020
Segments, Geographical Areas [Abstract]
Schedule Of Revenues By Geographic Region	The following presents revenues by geographic region (in thousands): Years Ended September 30, 2020 2019 2018 Americas: United States $ 1,221,190 $ 1,137,556 $ 1,088,270 Other 95,878 108,112 116,073 Total Americas 1,317,068 1,245,668 1,204,343 EMEA 593,307 553,701 546,239 Asia Pacific 440,447 443,078 410,825 $ 2,350,822 $ 2,242,447 $ 2,161,407
Schedule of Revenues by Systems and Software	The following presents net product revenues by systems and software (in thousands): Years Ended September 30, 2020 2019 2018 Net product revenues Systems revenue $ 668,313 $ 745,798 $ 810,182 Software revenue 357,543 239,793 149,926 Total net product revenue $ 1,025,856 $ 985,591 $ 960,108
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, 2020 2019 2018 Ingram Micro, Inc. 16.7 % 18.2 % 16.6 % Tech Data — 10.2 % 11.6 % Westcon Group, Inc. — 10.0 % 10.4 % Synnex Corporation — — 10.8 % Arrow ECS — — 10.7 %
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, 2020 2019 United States $ 190,509 $ 194,176 EMEA 20,361 13,451 Other countries 18,369 15,799 $ 229,239 $ 223,426

Quarterly Results Of Operatio_2

Quarterly Results Of Operations (Unaudited) (Tables)	12 Months Ended
	Sep. 30, 2020
Quarterly Financial Data [Abstract]
Schedule Of Quarterly Results Of Operations	Three Months Ended Sept. 30, 2020 June 30, 2020 March 31, 2020 Dec. 31, 2019 Sept. 30, 2019 June 30, 2019 March 31, 2019 Dec. 31, 2018 (unaudited and in thousands, except per share data) Net revenues Products $ 278,451 $ 253,331 $ 259,538 $ 234,536 $ 264,926 $ 248,929 $ 237,859 $ 233,877 Services 336,365 329,921 323,911 334,769 325,462 314,465 307,036 309,893 Total 614,816 583,252 583,449 569,305 590,388 563,394 544,895 543,770 Cost of net revenues Products 62,634 57,437 53,086 42,118 44,693 44,336 43,547 42,410 Services 49,333 48,603 48,152 46,524 46,225 46,431 44,631 44,304 Total 111,967 106,040 101,238 88,642 90,918 90,767 88,178 86,714 Gross profit 502,849 477,212 482,211 480,663 499,470 472,627 456,717 457,056 Operating expenses Sales and marketing 220,379 211,808 215,472 195,519 217,554 195,852 170,954 164,259 Research and development 120,300 115,991 109,028 96,005 102,812 116,894 96,314 92,038 General and administrative 63,557 61,792 74,013 59,004 64,390 57,141 46,656 42,543 Restructuring charges — — — 7,800 — — — — Total operating expenses 404,236 389,591 398,513 358,328 384,756 369,887 313,924 298,840 Income from operations 98,613 87,621 83,698 122,335 114,714 102,740 142,793 158,216 Other income, net (1,090) 141 (141) 5,220 3,397 4,722 7,434 7,095 Income before income taxes 97,523 87,762 83,557 127,555 118,111 107,462 150,227 165,311 Provision for income taxes 19,860 17,890 22,178 29,028 23,274 21,557 34,140 34,406 Net income $ 77,663 $ 69,872 $ 61,379 $ 98,527 $ 94,837 $ 85,905 $ 116,087 $ 130,905 Net income per share — basic $ 1.27 $ 1.15 $ 1.01 $ 1.62 $ 1.57 $ 1.43 $ 1.94 $ 2.17 Weighted average shares — basic 61,149 60,978 60,869 60,649 60,283 59,981 59,686 60,216 Net income per share — diluted $ 1.26 $ 1.14 $ 1.00 $ 1.62 $ 1.57 $ 1.43 $ 1.93 $ 2.16 Weighted average shares — diluted 61,636 61,415 61,084 60,815 60,448 60,196 60,029 60,645

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies - Narrative (Details) $ in Thousands	Jan. 24, 2020USD ($)	Sep. 30, 2020USD ($)segment	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)
Segment Reporting [Abstract]
Number of Reportable Segments | segment		1
Advertising
Advertising Expense		$ 7,800	$ 4,700	$ 4,600
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
Shape Security Inc.
Business Combinations
Total Purchase Price	$ 1,000,000
Shape Security Inc. | Developed Technology Rights
Business Combinations
Identifiable intangible assets:	$ 120,000
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
Geographic Concentration Risk [Member] | Customer One [Member] | Accounts Receivable [Member]
Concentration of Credit Risk
Concentration risk percentage		14.10%	12.40%
Geographic Concentration Risk [Member] | Customer Two [Member] | Accounts Receivable [Member]
Concentration of Credit Risk
Concentration risk percentage		11.40%	12.90%
Geographic Concentration Risk [Member] | Customer Three [Member] | Accounts Receivable [Member]
Concentration of Credit Risk
Concentration risk percentage			11.50%

Summary Of Significant Accoun_4

Summary Of Significant Accounting Policies - Schedule Of Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Accounting Policies [Abstract]
Finished goods	$ 17,096	$ 22,441
Raw materials	10,802	11,960
Inventories, Total	$ 27,898	$ 34,401

Summary Of Significant Accoun_5

Summary Of Significant Accounting Policies - Property And Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Property, Plant and Equipment [Line Items]
Computer equipment	$ 153,256	$ 142,372
Capitalized Computer Software, Gross	95,288	85,866
Office furniture and equipment	45,280	38,892
Leasehold improvements	175,593	151,055
Property and equipment, gross	469,417	418,185
Accumulated depreciation and amortization	(240,178)	(194,759)
Property, Plant and Equipment, Net	$ 229,239	$ 223,426
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	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Accounting Policies [Abstract]
Net income	$ 77,663	$ 69,872	$ 61,379	$ 98,527	$ 94,837	$ 85,905	$ 116,087	$ 130,905	$ 307,441	$ 427,734	$ 453,689
Weighted average shares outstanding - basic	61,149	60,978	60,869	60,649	60,283	59,981	59,686	60,216	60,911	60,044	61,262
Dilutive effect of common shares from stock options and restricted stock units									467	412	751
Weighted average shares outstanding - diluted	61,636	61,415	61,084	60,815	60,448	60,196	60,029	60,645	61,378	60,456	62,013
Basic net income per share (USD per share)	$ 1.27	$ 1.15	$ 1.01	$ 1.62	$ 1.57	$ 1.43	$ 1.94	$ 2.17	$ 5.05	$ 7.12	$ 7.41
Diluted net income per share (USD per share)	$ 1.26	$ 1.14	$ 1	$ 1.62	$ 1.57	$ 1.43	$ 1.93	$ 2.16	$ 5.01	$ 7.08	$ 7.32

Revenue from Contracts with C_3

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

Revenue from Contracts with C_4

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

Revenue from Contracts with C_5

Revenue from Contracts with Customers - Contract Assets and Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Change in Contract with Customer, Asset [Roll Forward]
Balance, beginning of year	$ 132,492	$ 0
Impacts from adoption of ASC 606	0	57,499
Revenue recognized during period but not yet billed	37,260	27,459
Contract asset net additions	123,533	88,068
Contract assets acquired through the purchase of Shape	6,045	0
Contract assets reclassified to accounts receivable	(98,858)	(40,534)
Balance, end of year	200,472	132,492
Change in Contract with Customer, Liability [Roll Forward]
Balance, beginning of year	1,198,116	1,015,321
Impacts from adoption of ASC 606	0	68,078
Amounts billed but not recognized as revenues	850,022	866,142
Amounts acquired through the purchase of Shape	39,000	0
Revenues recognized related to the opening balance of deferred revenue	(814,506)	(751,425)
Balance, end of year	$ 1,272,632	$ 1,198,116

Revenue from Contracts with C_6

Revenue from Contracts with Customers - Remaining Performance Obligations. (Details) $ in Billions	Sep. 30, 2020USD ($)
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Amount	$ 1.3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-10-01
Revenue from Contract with Customer [Abstract]
Revenue, Remaining Performance Obligation, Percentage	69.40%
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	19.00%

Business Combinations - Narrati

Business Combinations - Narrative (Details) - USD ($) $ in Thousands	Jan. 24, 2020	May 08, 2019	Sep. 30, 2020
Business Acquisition [Line Items]
Goodwill, Other Increase (Decrease)			$ 6,024
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
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
Goodwill, Other Increase (Decrease)			$ 6,000
Tax Deductible Goodwill		$ 490,300
F5 Networks Acquisition of Nginx | General and Administrative Expense
Business Acquisition [Line Items]
Transaction Costs		$ 1,000
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 | 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

Business Combinations - Purchas

Business Combinations - Purchase Price Allocation (Details) - USD ($) $ in Thousands	Jan. 24, 2020	May 08, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Fair value of tangible assets:
Goodwill			$ 1,858,966	$ 1,065,379	$ 555,965
Shape Security Inc.
Assets acquired
Cash and cash equivalents	$ 53,934
Fair value of tangible assets:
Accounts receivable	21,077
Deferred tax assets	24,619
Operating lease right-of-use assets	29,644
Other tangible assets	$ 22,571
Identifiable Intangible Assets Useful Life	6 years 6 months
Goodwill	$ 799,611
Total assets acquired	1,101,956
Liabilities assumed
Deferred revenue	(39,000)
Operating lease liabilities	(30,773)
Other assumed liabilities	(18,571)
Total liabilities assumed	(88,344)
Net assets acquired	1,013,612
Shape Security Inc. | Developed Technology Rights
Fair value of tangible assets:
Identifiable intangible assets:	$ 120,000
Identifiable Intangible Assets Useful Life	7 years
Shape Security Inc. | Customer Relationships
Fair value of tangible assets:
Identifiable intangible assets:	$ 21,000
Identifiable Intangible Assets Useful Life	4 years
Shape Security Inc. | Trade Names
Fair value of tangible assets:
Identifiable intangible assets:	$ 9,500
Identifiable Intangible Assets Useful Life	5 years
F5 Networks Acquisition of Nginx
Assets acquired
Cash and cash equivalents		$ 29,911
Fair value of tangible assets:
Other tangible assets		$ 23,699
Identifiable Intangible Assets Useful Life		8 years 1 month 6 days
Goodwill		$ 503,414
Total assets acquired		646,324
Liabilities assumed
Other assumed liabilities		(9,116)
Total liabilities assumed		(9,116)
Net assets acquired		637,208
F5 Networks Acquisition of Nginx | Developed Technology Rights
Fair value of tangible assets:
Identifiable intangible assets:		$ 62,500
Identifiable Intangible Assets Useful Life		7 years
F5 Networks Acquisition of Nginx | Customer Relationships
Fair value of tangible assets:
Identifiable intangible assets:		$ 12,000
Identifiable Intangible Assets Useful Life		15 years
F5 Networks Acquisition of Nginx | Trade Names
Fair value of tangible assets:
Identifiable intangible assets:		$ 14,500
Identifiable Intangible Assets Useful Life		7 years
F5 Networks Acquisition of Nginx | Non-competition Agreements
Fair value of tangible assets:
Identifiable intangible assets:		$ 300
Identifiable Intangible Assets Useful Life		2 years

Fair Value Measurements - Sched

Fair Value Measurements - Schedule Of Financial Assets Measured At Fair Value On A Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value	$ 250,970	$ 293,642
Available-for-sale securities	360,333	373,063
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	43,553	140,238
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	207,417	153,404
Corporate Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	102,939	298,916
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]
Available-for-sale securities	102,939	298,916
Municipal Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities		2,524
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]
Available-for-sale securities		2,524
US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities		5,515
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]
Available-for-sale securities		5,515
US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities		51,447
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]
Available-for-sale securities		51,447
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	714,242	1,025,107
Fair Value, Recurring [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]
Assets, Fair Value Disclosure	43,553	140,238
Fair Value, Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Assets, Fair Value Disclosure	670,689	884,869
US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	47,151	22,146
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]
Available-for-sale securities	47,151	22,146
US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	117,374	78,992
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]
Available-for-sale securities	117,374	78,992
Municipal Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	6,146	12,129
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]
Available-for-sale securities	6,146	12,129
Corporate Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	189,662	259,547
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]
Available-for-sale securities	$ 189,662	259,547
Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities		249
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]
Available-for-sale securities		$ 249

Fair Value Measurements - Impai

Fair Value Measurements - Impairment of Assets Measured at Fair Value on a Nonrecurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Assets Measured at Fair Value on a Nonrecurring Basis [Abstract]
Operating Lease, Impairment Loss	$ 9.7
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, 2020	Sep. 30, 2019
Net Investment Income [Line Items]
Cost or Amortized Cost	$ 359,586	$ 372,745
Gross Unrealized Gains	756	435
Gross Unrealized Losses	(9)	(117)
Fair Value	360,333	373,063
Corporate Debt Securities [Member]
Net Investment Income [Line Items]
Cost or Amortized Cost	102,206	298,888
Gross Unrealized Gains	756	469
Gross Unrealized Losses	(23)	(441)
Fair Value	102,939	298,916
Municipal Bonds And Notes [Member]
Net Investment Income [Line Items]
Cost or Amortized Cost		2,528
Gross Unrealized Gains		2
Gross Unrealized Losses		(6)
Fair Value		2,524
US Government Debt Securities [Member]
Net Investment Income [Line Items]
Cost or Amortized Cost		5,515
Gross Unrealized Gains		3
Gross Unrealized Losses		(3)
Fair Value		5,515
US Government Agencies Debt Securities [Member]
Net Investment Income [Line Items]
Cost or Amortized Cost		51,463
Gross Unrealized Gains		5
Gross Unrealized Losses		(21)
Fair Value		51,447
Long-Term Investments [Member]
Net Investment Income [Line Items]
Cost or Amortized Cost	102,206	358,394
Gross Unrealized Gains	756	479
Gross Unrealized Losses	(23)	(471)
Fair Value	102,939	358,402
Certificates of Deposit [Member]
Net Investment Income [Line Items]
Cost or Amortized Cost		249
Gross Unrealized Gains		0
Gross Unrealized Losses		0
Fair Value		249
Corporate Debt Securities [Member]
Net Investment Income [Line Items]
Cost or Amortized Cost	188,932	259,242
Gross Unrealized Gains	736	402
Gross Unrealized Losses	(6)	(97)
Fair Value	189,662	259,547
Municipal Bonds And Notes [Member]
Net Investment Income [Line Items]
Cost or Amortized Cost	6,143	12,128
Gross Unrealized Gains	3	6
Gross Unrealized Losses	0	(5)
Fair Value	6,146	12,129
US Government Debt Securities [Member]
Net Investment Income [Line Items]
Cost or Amortized Cost	117,363	78,988
Gross Unrealized Gains	14	18
Gross Unrealized Losses	(3)	(14)
Fair Value	117,374	78,992
US Government Agencies Debt Securities [Member]
Net Investment Income [Line Items]
Cost or Amortized Cost	47,148	22,138
Gross Unrealized Gains	3	9
Gross Unrealized Losses	0	(1)
Fair Value	$ 47,151	$ 22,146

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, 2020	Sep. 30, 2019
Debt Securities, Available-for-sale [Line Items]
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months	$ 85,304	$ 296,652
Available-For-Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses Accumulated In Investments	(31)	(468)
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater	5,006	127,404
Available-For-Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Aggregate Losses Accumulated In Investments	(1)	(120)
Fair Value, Continuous Loss Position, Unrealized Loss, Total	90,310	424,056
Available-For-Sale Securities, Continuous Unrealized Loss Position, Aggregate Losses Accumulated In Investments	(32)	(588)
Corporate Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months	43,492	237,747
Available-For-Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses Accumulated In Investments	(28)	(434)
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater	5,006	109,613
Available-For-Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Aggregate Losses Accumulated In Investments	(1)	(104)
Fair Value, Continuous Loss Position, Unrealized Loss, Total	48,498	347,360
Available-For-Sale Securities, Continuous Unrealized Loss Position, Aggregate Losses Accumulated In Investments	(29)	(538)
Municipal Bonds And Notes [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months		864
Available-For-Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses Accumulated In Investments		0
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater		7,800
Available-For-Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Aggregate Losses Accumulated In Investments		(11)
Fair Value, Continuous Loss Position, Unrealized Loss, Total		8,664
Available-For-Sale Securities, Continuous Unrealized Loss Position, Aggregate Losses Accumulated In Investments		(11)
US Government Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months	41,812	27,095
Available-For-Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses Accumulated In Investments	(3)	(12)
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater	0	9,991
Available-For-Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Aggregate Losses Accumulated In Investments	0	(5)
Fair Value, Continuous Loss Position, Unrealized Loss, Total	41,812	37,086
Available-For-Sale Securities, Continuous Unrealized Loss Position, Aggregate Losses Accumulated In Investments	$ (3)	(17)
US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months		30,946
Available-For-Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses Accumulated In Investments		(22)
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater		0
Available-For-Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Aggregate Losses Accumulated In Investments		0
Fair Value, Continuous Loss Position, Unrealized Loss, Total		30,946
Available-For-Sale Securities, Continuous Unrealized Loss Position, Aggregate Losses Accumulated In Investments		$ (22)

Short-Term And Long-Term Inve_5

Short-Term And Long-Term Investments - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Investments, Debt and Equity Securities [Abstract]
Investment Income, Interest	$ 12.2	$ 25.3	$ 17

Balance Sheet Details - Narrati

Balance Sheet Details - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 95,857	$ 68,507	$ 59,491
Capitalized Computer Software, Impairments		6,300
Property, Plant and Equipment [Member]
Property, Plant and Equipment [Line Items]
Depreciation and amortization	$ 59,500	$ 58,000	$ 45,900

Balance Sheet Details - Cash, C

Balance Sheet Details - Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Balance Sheet Details [Abstract]
Cash and Cash Equivalents, at Carrying Value	$ 849,556	$ 599,219
Restricted Cash	3,270	3,035
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	$ 852,826	$ 602,254	$ 425,894	$ 674,452

Balance Sheet Details - Invento

Balance Sheet Details - Inventories (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Balance Sheet Details [Abstract]
Finished goods	$ 17,096	$ 22,441
Raw materials	10,802	11,960
Inventory, Net	$ 27,898	$ 34,401

Balance Sheet Details - Other C

Balance Sheet Details - Other Current Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Balance Sheet Details [Abstract]
Contract assets	$ 138,096	$ 79,407
Prepaid expenses	47,197	49,051
Capitalized contract acquisition costs	29,650	28,228
Other	44,563	26,188
Other Assets, Current	$ 259,506	$ 182,874

Balance Sheet Details - Propert

Balance Sheet Details - Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Balance Sheet Details [Abstract]
Machinery and Equipment, Gross	$ 153,256	$ 142,372
Capitalized Computer Software, Gross	95,288	85,866
Furniture and Fixtures, Gross	45,280	38,892
Leasehold Improvements, Gross	175,593	151,055
Property, Plant and Equipment, Gross	469,417	418,185
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(240,178)	(194,759)
Property, Plant and Equipment, Net	$ 229,239	$ 223,426

Balance Sheet Details - Goodwil

Balance Sheet Details - Goodwill (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Balance Sheet Details [Abstract]
Goodwill, Beginning Balance	$ 1,065,379	$ 555,965
Goodwill, Acquired During Period	799,611	509,414
Goodwill, Other Increase (Decrease)	6,024
Goodwill, Ending Balance	$ 1,858,966	$ 1,065,379

Balance Sheet Details - Other A

Balance Sheet Details - Other Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Balance Sheet Details [Abstract]
Intangible assets	$ 225,900	$ 108,903
Contract assets	62,377	53,085
Capitalized contract acquisition costs	40,746	31,218
Other	18,424	10,575
Other Assets, Noncurrent	$ 347,447	$ 203,781

Balance Sheet Details - Intangi

Balance Sheet Details - Intangible Assets (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 334,908	$ 183,308
Accumulated Amortization	(109,008)	(74,405)
Net Carrying Amount	225,900	108,903
Amortization of Intangible Assets	34,600	11,800	$ 11,100
Developed Technology Rights
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	246,173	126,173
Accumulated Amortization	(76,556)	(53,213)
Net Carrying Amount	169,617	72,960
Customer Relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	41,242	20,242
Accumulated Amortization	(10,657)	(5,533)
Net Carrying Amount	30,585	14,709
Patents And Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	20,260	19,160
Accumulated Amortization	(14,448)	(11,800)
Net Carrying Amount	5,812	7,360
Trade Names
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	24,973	15,473
Accumulated Amortization	(5,174)	(1,836)
Net Carrying Amount	19,799	13,637
Non-Compete Covenants [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2,260	2,260
Accumulated Amortization	(2,173)	(2,023)
Net Carrying Amount	$ 87	$ 237

Balance Sheet Details - Estimat

Balance Sheet Details - Estimated Amortization Expense For Intangible Assets (Details) $ in Thousands	Sep. 30, 2020USD ($)
Balance Sheet Details [Abstract]
2021	$ 42,722
2022	41,429
2023	40,625
2024	35,360
2025	29,624
Total estimated amortization expense	$ 189,760

Balance Sheet Details - Accrued

Balance Sheet Details - Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Balance Sheet Details [Abstract]
Payroll and benefits	$ 169,708	$ 138,453
Operating lease liabilities, current	46,010	0
Income and other tax accruals	33,048	31,801
Other	72,632	65,615
Accrued Liabilities, Current	$ 321,398	$ 235,869

Balance Sheet Details - Other L

Balance Sheet Details - Other Long-term Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Balance Sheet Details [Abstract]
Deferred rent	$ 0	$ 66,103
Income taxes payable	49,846	42,324
Other	9,665	23,426
Other Liabilities, Noncurrent	$ 59,511	$ 131,853

Debt Facilities - Narrative (De

Debt Facilities - Narrative (Details)	Jan. 31, 2020USD ($)	Jan. 24, 2020USD ($)	Sep. 30, 2020USD ($)extension
Term Loan Facility [Member]
Debt Instrument [Line Items]
Aggregate Principal Amount		$ 400,000,000
Debt Issuance Costs		$ 2,200,000	$ 1,700,000
Redemption Percentage		1.25%
Long-term Debt			$ 390,000,000
Interest Rate at Period End			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%

Debt Facilities - Long-term Deb

Debt Facilities - Long-term Debt Maturities (Details) - Term Loan Facility [Member] $ in Thousands	Sep. 30, 2020USD ($)
Debt Instrument [Line Items]
2021	$ 20,000
2022	20,000
2023	350,000
Total	$ 390,000

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2020USD ($)ft²	Oct. 01, 2019USD ($)	Sep. 30, 2019USD ($)
Lessee, Lease, Description [Line Items]
Operating lease right-of-use assets	$ 300,680		$ 0
Operating Lease, Impairment Loss	9,700
Sublease Income	10,200
Lessor, Operating Lease, Payments to be Received, Next Twelve Months	4,500
Lessor, Operating Lease, Payments to be Received, Two To Three Years	$ 5,700
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

Leases - Operating Lease Expens

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

Leases - Supplemental Balance S

Leases - Supplemental Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Leases [Abstract]
Operating lease right-of-use assets	$ 300,680	$ 0
Operating lease liabilities, current	46,010	0
Operating lease liabilities, long-term	338,715	$ 0
Total lease liabilities	$ 384,725
Weighted average remaining lease term (in years)	10 years 2 months 12 days
Weighted average discount rate	2.58%

Leases - Maturities of Lease Li

Leases - Maturities of Lease Liabilities (Details) $ in Thousands	Sep. 30, 2020USD ($)
Leases [Abstract]
2021	$ 55,601
2022	56,813
2023	44,041
2024	39,590
2025	33,215
Thereafter	217,506
Total lease payments	446,766
Less: imputed interest	(62,041)
Total lease liabilities	$ 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

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Operating Loss Carryforwards [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent	21.00%	24.50%
Income Tax Holiday, Aggregate Dollar Amount	$ 8,200	$ 8,100	$ 6,400
Income Tax Holiday, Income Tax Benefits Per Share	$ 0.13	$ 0.13	$ 0.10
Deferred Tax Assets, Operating Loss Carryforwards	$ 54,842	$ 12,269
Deferred Tax Assets, Tax Credit Carryforwards	15,807	13,783
Valuation Allowance, Deferred Tax Asset, Change in Amount	9,100	700
Unrecognized Tax Benefits	51,767	42,287	$ 31,672	$ 23,135
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	34,300	29,400	23,100
Unrecognized Tax Benefits, Period Increase (Decrease)	(1,000)	2,400	$ 400
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	3,000	$ 4,000
Foreign [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry-forwards, net	59,500
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	3,400
Deferred Tax Assets, Tax Credit Carryforwards	4,000
Domestic Tax Authority [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry-forwards, net	111,800
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	58,900
Deferred Tax Assets, Operating Loss Carryforwards	170,700
Deferred Tax Assets, Tax Credit Carryforwards	500
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry-forwards, net	158,200
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	221,400
Deferred Tax Assets, Operating Loss Carryforwards	379,600
Deferred Tax Assets, Tax Credit Carryforwards	15,600
Deferred Tax Assets, Tax Credit Carryforwards, Subject to Expiration	$ 3,700

Income Taxes - Components Of In

Income Taxes - Components Of Income Before Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
United States									$ 216,409	$ 360,648	$ 441,336
International									179,988	180,463	162,424
Income before income taxes	$ 97,523	$ 87,762	$ 83,557	$ 127,555	$ 118,111	$ 107,462	$ 150,227	$ 165,311	$ 396,397	$ 541,111	$ 603,760

Income Taxes - Schedule Of Prov

Income Taxes - Schedule Of Provision For Income Taxes (Benefit) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Current, U.S. federal									$ 26,978	$ 43,039	$ 78,454
Current, State									4,230	13,864	9,800
Current, Foreign									50,368	49,197	41,040
Total									81,576	106,100	129,294
Deferred, U.S. federal									10,875	8,716	21,259
Deferred, State									(1,121)	1,617	725
Deferred, Foreign									(2,374)	(3,056)	(1,207)
Total									7,380	7,277	20,777
Income taxes (benefit)	$ 19,860	$ 17,890	$ 22,178	$ 29,028	$ 23,274	$ 21,557	$ 34,140	$ 34,406	$ 88,956	$ 113,377	$ 150,071

Income Taxes - Schedule Of Effe

Income Taxes - Schedule Of Effective Tax Rate Differs From The U.S. Federal Statutory Rate (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Income Tax Disclosure [Abstract]
Income tax provision at statutory rate									$ 83,243	$ 113,633	$ 147,921
State taxes, net of federal benefit									4,258	14,206	9,349
Tax impact of foreign operations									(7,693)	(9,161)	(6,696)
Research and development and other credits									(11,843)	(12,760)	(13,159)
Domestic manufacturing deduction									0	0	(9,722)
Stock-based and other compensation									18,002	6,771	(150)
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsActAmount									0	0	21,015
Other									2,989	688	1,513
Income taxes (benefit)	$ 19,860	$ 17,890	$ 22,178	$ 29,028	$ 23,274	$ 21,557	$ 34,140	$ 34,406	$ 88,956	$ 113,377	$ 150,071

Income Taxes - Schedule Of Tax

Income Taxes - Schedule Of Tax Effects To Deferred Tax Assets And Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Net operating loss carry-forwards	$ 54,842	$ 12,269
Accrued compensation and benefits	13,162	13,478
Stock-based compensation	13,010	7,144
Deferred revenue	40,577	35,247
Lease liabilities	19,656	17,313
Other accruals and reserves	17,384	15,786
Tax credit carryforwards	15,807	13,783
Depreciation	620	592
Total deferred tax assets before deferred liabilities	175,058	115,612
Valuation allowance	(32,587)	(23,495)
Deferred tax assets, net of valuation allowance	142,471	92,117
Purchased intangibles	(46,491)	(10,560)
Depreciation	(34,757)	(39,910)
Deferred Tax Liabilities, Deferred Expense, Other Capitalized Costs	(11,924)	(10,656)
Deferred Tax Liabilities, Deferred Expense, Reserves and Accruals	(4,728)	(3,603)
Total deferred tax liabilities	(97,900)	(64,729)
Net deferred tax assets	$ 44,571	$ 27,388

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, 2020	Sep. 30, 2019	Sep. 30, 2018
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance, beginning of period	$ 42,287	$ 31,672	$ 23,135
Gross increases related to prior period tax positions	8,664	5,129	2,715
Gross decreases related to prior period tax positions	(1,051)	(287)	0
Gross increases related to current period tax positions	9,272	7,756	8,230
Decreases relating to settlements with tax authorities	(3,578)	0	0
Reductions due to lapses of statute of limitations	(3,827)	(1,983)	(2,408)
Balance, end of period	$ 51,767	$ 42,287	$ 31,672

Shareholders' Equity - Narrativ

Shareholders' Equity - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			12 Months Ended
	Sep. 30, 2020	Aug. 31, 2020	Jul. 31, 2020	Sep. 30, 2020	Oct. 31, 2018	Oct. 25, 2017
Common Stock Repurchase [Line Items]
Stock Repurchased and Retired During Period, Shares	0	357,644	0	799,495
Treasury Stock Acquired, Average Cost Per Share	$ 0	$ 139.79	$ 0	$ 125.10
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 1,272,511	$ 1,272,511	$ 1,322,518	$ 1,272,511
October Twenty Six Two Thousand Ten Program [Member]
Common Stock Repurchase [Line Items]
Stock Repurchase Program, Authorized Amount					$ 1,000,000	$ 4,400,000

Shareholders' Equity - Common S

Shareholders' Equity - Common Stock Repurchased and Retired Table (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended			3 Months Ended	12 Months Ended
	Sep. 30, 2020	Aug. 31, 2020	Jul. 31, 2020	Sep. 30, 2020	Sep. 30, 2020
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Shares	0	357,644	0		799,495
Treasury Stock Acquired, Average Cost Per Share	$ 0	$ 139.79	$ 0		$ 125.10
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 1,272,511	$ 1,272,511	$ 1,322,518	$ 1,272,511	$ 1,272,511
Cost of Issuance of Treasury Stock, Shares				15,434
October Twenty Six Two Thousand Ten Program and Cost of Issuance of Treasury Stock [Member]
Equity, Class of Treasury Stock [Line Items]
Stock Repurchased and Retired During Period, Shares	0	373,078	0

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, 2020	Sep. 30, 2019	Sep. 30, 2018
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	1.10%	2.25%	1.14%
Expected volatility	26.32%	18.14%	22.03%
Maximum
Fair Value Assumptions
Risk-free interest rate	1.97%	2.51%	1.77%
Expected volatility	41.94%	31.74%	24.87%
Two Thousand Eleven Employee Stock Purchase Plan [Member]
Fair Value Assumptions
Expected term	6 months

Stock-Based Compensation - Narr

Stock-Based Compensation - Narrative (Details) - USD ($)	Oct. 30, 2020	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	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		$ 201,900,000	$ 162,900,000	$ 157,900,000
Share-based Payment Arrangement, Expense, Tax Benefit		37,600,000	$ 31,300,000	$ 34,600,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount		$ 205,600,000
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition		2 years
Expected term		6 months	6 months	6 months
Vested and expected to vest, Number of Shares		368,503
Weighted Average Grant Date Fair Value		$ 137.84	$ 165.64	$ 126.86
Fair market value of restricted stock vested		$ 138,400,000	$ 159,600,000	$ 182,600,000
Total intrinsic value of options exercised		$ 11,400,000	$ 700,000	$ 100,000
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity Instruments Other than Options, Grants in Period	1,451,566
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		1,899,745
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		121,820
Nginx, Inc. 2011 Share Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance						302,634
Shares available for purchase under stock option plan		131,342
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		17,986
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]
Shares Issued in Period		411,385
Outstanding stock units		377,066
Shape 2011 Share Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance					501,085
Vested and expected to vest, Number of Shares		259,709
Shape 2011 Share Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued in Period		7,703
Outstanding stock units		5,631
Shape 2011 Share Plan [Member] | Share-based Payment Arrangement, Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued in Period		334,709
Two Thousand Fourteen Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance		21,280,000
Vesting rate of stock options and awards upon certain changes in ownership control		50.00%
Number of Shares Authorized		2,453,277
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		152,199
Outstanding stock units		145,869	55,184
Weighted Average Grant Date Fair Value		$ 146.42	$ 165.83
Equity Instruments Other than Options, Grants in Period		152,199
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		1,237,609
Outstanding stock units		1,204,290	1,041,889
Weighted Average Grant Date Fair Value		$ 146.39	$ 158.10
Equity Instruments Other than Options, Grants in Period		1,237,609

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule Of Summary Of Restricted Stock Unit Activity (Details)	12 Months Ended
	Sep. 30, 2020$ / sharesshares
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning balance	$ 165.64
Weighted Average Grant Date Fair Value, Ending balance	$ 137.84
Performance Shares [Member] | Two Thousand Fourteen Equity Incentive Plan [Member]
Outstanding Restricted Stock Units
Outstanding Stock Units, Beginning balance | shares	55,184
Outstanding Stock Units, Units granted | shares	152,199
Outstanding Stock Units, Units vested | shares	(42,053)
Outstanding Stock Units, Units cancelled | shares	(19,461)
Outstanding Stock Units, Ending balance | shares	145,869
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning balance	$ 165.83
Weighted Average Grant Date Fair Value, Units granted	147.30
Weighted Average Grant Date Fair Value, Units vested	142.01
Weighted Average Grant Date Fair Value, Units cancelled	157.81
Weighted Average Grant Date Fair Value, Ending balance	$ 146.42
Restricted Stock Units (RSUs) [Member] | Two Thousand Fourteen Equity Incentive Plan [Member]
Outstanding Restricted Stock Units
Outstanding Stock Units, Beginning balance | shares	1,041,889
Outstanding Stock Units, Units granted | shares	1,237,609
Outstanding Stock Units, Units vested | shares	(933,413)
Outstanding Stock Units, Units cancelled | shares	(141,795)
Outstanding Stock Units, Ending balance | shares	1,204,290
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning balance	$ 158.10
Weighted Average Grant Date Fair Value, Units granted	142.58
Weighted Average Grant Date Fair Value, Units vested	134.49
Weighted Average Grant Date Fair Value, Units cancelled	150.58
Weighted Average Grant Date Fair Value, Ending balance	$ 146.39

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, 2020	Sep. 30, 2019	Sep. 30, 2018
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	$ 196.02
Expected term	10 months 28 days
Risk-free interest rate	1.53%
Expected dividend	0.00%
Tranche 1 [Member] | F5 Networks [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	27.61%
Tranche 1 [Member] | Index Members [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	26.88%
Tranche 2 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair Value, Per Share	$ 199.85
Expected term	1 year 10 months 28 days
Risk-free interest rate	1.55%
Expected dividend	0.00%
Tranche 2 [Member] | F5 Networks [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	26.22%
Tranche 2 [Member] | Index Members [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	26.70%
Tranche 3 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair Value, Per Share	$ 202.56
Expected term	2 years 10 months 28 days
Risk-free interest rate	1.54%
Expected dividend	0.00%
Tranche 3 [Member] | F5 Networks [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	24.90%
Tranche 3 [Member] | Index Members [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	24.82%

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, 2020	Sep. 30, 2019	Sep. 30, 2018
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 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
Annual Equity Program [Member] | November 1, 2016 [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity Instruments Other than Options, Grants in Period	115,347
Award vesting period	4 years

Stock-Based Compensation - Sc_5

Stock-Based Compensation - Schedule Of Stock Option Activity (Details)	12 Months Ended
	Sep. 30, 2020$ / sharesshares
Number of Shares
Number of Shares, Beginning balance | shares	207,759
Number of Shares, Options granted | shares	334,709
Number of Shares, Options exercised | shares	(104,487)
Number of Shares, Options cancelled | shares	(46,881)
Number of Shares, Ending balance | shares	391,100
Weighted Average Exercise Price per Share
Weighted Average Exercise Price per Share, Beginning balance | $ / shares	$ 24.43
Weighted Average Exercise Price per Share, Options granted | $ / shares	41.10
Weighted Average Exercise Price per Share, Options exercised | $ / shares	24.84
Weighted Average Exercise Price per Share, Options cancelled | $ / shares	40.09
Weighted Average Exercise Price per Share, Ending balance | $ / shares	$ 36.71

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, 2020	Sep. 30, 2019
Share-based Payment Arrangement, Noncash Expense [Abstract]
Stock options outstanding	391,100	207,759
Stock options outstanding, Weighted Average Remaining Contractual Life (in Years)	7 years 9 months 21 days
Stock options outstanding, Weighted Average Exercise Price per Share	$ 36.71	$ 24.43
Stock options outstanding, Aggregate Intrinsic Value	$ 34,236
Exercisable, Number of Shares	119,734
Exercisable, Weighted Average Remaining Contractual Life (in Years)	7 years 1 month 9 days
Exercisable, Weighted Average Exercise Price per Share	$ 25.38
Exercisable, Aggregate Intrinsic Value	$ 11,683
Vested and expected to vest, Number of Shares	368,503
Vested and expected to vest, Weighted Average Remaining Contractual Life (in Years)	7 years 9 months 7 days
Vested and expected to vest, Weighted Average Exercise Price per Share	$ 36.04
Vested and expected to vest, Aggregate Intrinsic Value	$ 32,477

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, 2020shares
Awards Available for Grant
Awards Available for Grant, Beginning balance	2,939,974
Awards Available for Grant, Granted	(2,143,605)
Awards Available for Grant, Cancelled	266,925
Additional shares reserved (terminated), net	1,651,664
Awards Available for Grant, Ending balance	2,714,958

Net Income Per Share (Details)

Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Net Income Per Share [Abstract]
Net income	$ 77,663	$ 69,872	$ 61,379	$ 98,527	$ 94,837	$ 85,905	$ 116,087	$ 130,905	$ 307,441	$ 427,734	$ 453,689
Weighted average shares - basic (shares)	61,149	60,978	60,869	60,649	60,283	59,981	59,686	60,216	60,911	60,044	61,262
Weighted Average Number Diluted Shares Outstanding Adjustment									467	412	751
Weighted Average Number of Shares Outstanding, Diluted	61,636	61,415	61,084	60,815	60,448	60,196	60,029	60,645	61,378	60,456	62,013
Net income per share - basic (USD per share)	$ 1.27	$ 1.15	$ 1.01	$ 1.62	$ 1.57	$ 1.43	$ 1.94	$ 2.17	$ 5.05	$ 7.12	$ 7.41
Net income per share - diluted (USD per share)	$ 1.26	$ 1.14	$ 1	$ 1.62	$ 1.57	$ 1.43	$ 1.93	$ 2.16	$ 5.01	$ 7.08	$ 7.32

Commitments And Contingencies -

Commitments And Contingencies - Narrative (Details) $ in Millions	Sep. 30, 2020USD ($)
Purchase Commitment [Member]
Commitments And Contingencies [Line Items]
Purchase Commitment, Remaining Minimum Amount Committed	$ 18.1

Restructuring Charges (Details)

Restructuring Charges (Details) $ in Thousands	3 Months Ended									12 Months Ended
	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)employee	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2018USD ($)employee	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)
Restructuring and Related Activities [Abstract]
Number of Employees in Reduction of Force Program | employee				75					215
Restructuring charges	$ 0	$ 0	$ 0	$ 7,800	$ 0	$ 0	$ 0	$ 0	$ 18,400	$ 7,800	$ 0	$ 18,426
Restructuring Reserve	$ 161				$ 0				$ 8,300	$ 161	$ 0	$ 8,300

Restructuring Charges - Restruc

Restructuring Charges - Restructuring Activity (Details) - USD ($) $ in Thousands	3 Months Ended									12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Restructuring and Related Activities [Abstract]
Accrued Expenses (Beginning Balance)				$ 0				$ 8,300		$ 0	$ 8,300
Restructuring charges	$ 0	$ 0	$ 0	$ 7,800	$ 0	$ 0	$ 0	$ 0	$ 18,400	7,800	0	$ 18,426
Cash payments										(7,639)
Non-cash items										0
Accrued Expenses (Ending Balance)	$ 161				$ 0				$ 8,300	$ 161	$ 0	$ 8,300

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Contributions by the Company to the plan	$ 11.3	$ 10.5	$ 10.5
Employer contribution, vesting period	4 years

Segment Information (Details)

Segment Information (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020USD ($)	Jun. 30, 2020USD ($)	Mar. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Sep. 30, 2020USD ($)geographic_regionsegment	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | segment									1
Number of Geographic Regions | geographic_region									3
Net revenues	$ 614,816	$ 583,252	$ 583,449	$ 569,305	$ 590,388	$ 563,394	$ 544,895	$ 543,770	$ 2,350,822	$ 2,242,447	$ 2,161,407
Property and equipment, net	229,239				223,426				229,239	223,426
Product [Member]
Segment Reporting Information [Line Items]
Net revenues	278,451	$ 253,331	$ 259,538	$ 234,536	264,926	$ 248,929	$ 237,859	$ 233,877	1,025,856	985,591	960,108
Product [Member] | Systems
Segment Reporting Information [Line Items]
Net revenues									668,313	745,798	810,182
Product [Member] | Software
Segment Reporting Information [Line Items]
Net revenues									357,543	239,793	149,926
United States [Member]
Segment Reporting Information [Line Items]
Net revenues									1,221,190	1,137,556	1,088,270
Property and equipment, net	190,509				194,176				190,509	194,176
Other Americas [Member]
Segment Reporting Information [Line Items]
Net revenues									95,878	108,112	116,073
Americas [Member]
Segment Reporting Information [Line Items]
Net revenues									1,317,068	1,245,668	1,204,343
EMEA [Member]
Segment Reporting Information [Line Items]
Net revenues									593,307	553,701	546,239
Property and equipment, net	20,361				13,451				20,361	13,451
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net revenues									440,447	443,078	$ 410,825
Other International Countries [Member]
Segment Reporting Information [Line Items]
Property and equipment, net	$ 18,369				$ 15,799				$ 18,369	$ 15,799
Customer One [Member] | Geographic Concentration Risk [Member] | Revenue Benchmark [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage									16.70%	18.20%	16.60%
Customer Two [Member] | Geographic Concentration Risk [Member] | Revenue Benchmark [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage									0.00%	10.20%	11.60%
Customer Three [Member] | Geographic Concentration Risk [Member] | Revenue Benchmark [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage									0.00%	10.00%	10.40%
Customer Four [Member] | Geographic Concentration Risk [Member] | Revenue Benchmark [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage									0.00%	0.00%	10.80%
Customer Five [Member] | Geographic Concentration Risk [Member] | Revenue Benchmark [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage									0.00%	0.00%	10.70%

Quarterly Results Of Operatio_3

Quarterly Results Of Operations (Unaudited) - Schedule Of Quarterly Results Of Operations (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended									12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Net revenues	$ 614,816	$ 583,252	$ 583,449	$ 569,305	$ 590,388	$ 563,394	$ 544,895	$ 543,770		$ 2,350,822	$ 2,242,447	$ 2,161,407
Cost of net revenues	111,967	106,040	101,238	88,642	90,918	90,767	88,178	86,714		407,887	356,577	361,481
Gross profit	502,849	477,212	482,211	480,663	499,470	472,627	456,717	457,056		1,942,935	1,885,870	1,799,926
Sales and marketing	220,379	211,808	215,472	195,519	217,554	195,852	170,954	164,259		843,178	748,619	664,135
Research and development	120,300	115,991	109,028	96,005	102,812	116,894	96,314	92,038		441,324	408,058	366,084
General and administrative	63,557	61,792	74,013	59,004	64,390	57,141	46,656	42,543		258,366	210,730	160,382
Restructuring charges	0	0	0	7,800	0	0	0	0	$ 18,400	7,800	0	18,426
Total	404,236	389,591	398,513	358,328	384,756	369,887	313,924	298,840		1,550,668	1,367,407	1,209,027
Income from operations	98,613	87,621	83,698	122,335	114,714	102,740	142,793	158,216		392,267	518,463	590,899
Other income, net	(1,090)	141	(141)	5,220	3,397	4,722	7,434	7,095		4,130	22,648	12,861
Income before income taxes	97,523	87,762	83,557	127,555	118,111	107,462	150,227	165,311		396,397	541,111	603,760
Provision for income taxes	19,860	17,890	22,178	29,028	23,274	21,557	34,140	34,406		88,956	113,377	150,071
Net income	$ 77,663	$ 69,872	$ 61,379	$ 98,527	$ 94,837	$ 85,905	$ 116,087	$ 130,905		$ 307,441	$ 427,734	$ 453,689
Net income per share - basic (USD per share)	$ 1.27	$ 1.15	$ 1.01	$ 1.62	$ 1.57	$ 1.43	$ 1.94	$ 2.17		$ 5.05	$ 7.12	$ 7.41
Weighted average shares - basic (shares)	61,149	60,978	60,869	60,649	60,283	59,981	59,686	60,216		60,911	60,044	61,262
Net income per share - diluted (USD per share)	$ 1.26	$ 1.14	$ 1	$ 1.62	$ 1.57	$ 1.43	$ 1.93	$ 2.16		$ 5.01	$ 7.08	$ 7.32
Weighted average shares - diluted (shares)	61,636	61,415	61,084	60,815	60,448	60,196	60,029	60,645		61,378	60,456	62,013
Product [Member]
Net revenues	$ 278,451	$ 253,331	$ 259,538	$ 234,536	$ 264,926	$ 248,929	$ 237,859	$ 233,877		$ 1,025,856	$ 985,591	$ 960,108
Cost of net revenues	62,634	57,437	53,086	42,118	44,693	44,336	43,547	42,410		215,275	174,986	181,061
Service [Member]
Net revenues	336,365	329,921	323,911	334,769	325,462	314,465	307,036	309,893		1,324,966	1,256,856	1,201,299
Cost of net revenues	$ 49,333	$ 48,603	$ 48,152	$ 46,524	$ 46,225	$ 46,431	$ 44,631	$ 44,304		$ 192,612	$ 181,591	$ 180,420

Uncategorized Items - ffiv-2020

Label	Element	Value
Accounting Standards Update 2014-09 [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 36,048,000
Accounting Standards Update 2014-09 [Member] | Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 36,048,000