F5 (FFIV) 10-K 21 Nov 18 2018 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($)	12 Months Ended
	Sep. 30, 2018	Nov. 15, 2018	Mar. 31, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	F5 NETWORKS INC
Entity Central Index Key	1,048,695
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	Sep. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		60,627,214
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 8,818,001,249

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
ASSETS
Cash and cash equivalents	$ 424,707	$ 673,228
Short-term investments	614,705	343,700
Accounts receivable, net of allowances of $2,040 and $1,815	295,352	291,924
Inventories	30,568	29,834
Other current assets	52,326	67,538
Total current assets	1,417,658	1,406,224
Property and equipment, net	145,042	122,420
Long-term investments	411,184	284,802
Deferred tax assets	33,441	53,303
Goodwill	555,965	555,965
Other assets, net	42,186	53,775
Total assets	2,605,476	2,476,489
LIABILITIES AND SHAREHOLDERS’ EQUITY
Accounts payable	57,757	50,760
Accrued liabilities	180,979	187,379
Deferred revenue	715,697	696,404
Total current liabilities	954,433	934,543
Other long-term liabilities	65,892	44,589
Deferred revenue, long-term	299,624	267,902
Deferred tax liabilities	35	63
Total long-term liabilities	365,551	312,554
Commitments and contingencies (Note 7)
Shareholders’ equity
Preferred stock, no par value; 10,000 shares authorized, no shares outstanding	0	0
Common stock, no par value; 200,000 shares authorized, 60,215 and 62,594 shares issued and outstanding	20,427	17,627
Accumulated other comprehensive loss	(22,178)	(17,997)
Retained earnings	1,287,243	1,229,762
Total shareholders’ equity	1,285,492	1,229,392
Total liabilities and shareholders’ equity	$ 2,605,476	$ 2,476,489

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Statement of Financial Position [Abstract]
Accounts receivable, allowances	$ 2,040	$ 1,815
Preferred stock, par value (USD per share)	$ 0	$ 0
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value (USD per share)	$ 0	$ 0
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	60,215,000	62,594,000
Common stock, shares outstanding	60,215,000	62,594,000

Consolidated Income Statements

Consolidated Income Statements - USD ($) shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Net revenues
Products	$ 256,412	$ 238,835	$ 237,558	$ 227,303	$ 248,990	$ 235,109	$ 241,080	$ 239,483	$ 960,108	$ 964,662	$ 944,469
Services	306,297	303,368	295,746	295,888	289,008	282,728	277,168	276,475	1,201,299	1,125,379	1,050,565
Total	562,709	542,203	533,304	523,191	537,998	517,837	518,248	515,958	2,161,407	2,090,041	1,995,034
Cost of net revenues
Products	48,505	45,164	44,127	43,265	46,641	43,787	43,928	41,676	181,061	176,032	166,624
Services	44,935	45,845	45,518	44,122	43,900	45,983	43,984	43,586	180,420	177,453	170,581
Total	93,440	91,009	89,645	87,387	90,541	89,770	87,912	85,262	361,481	353,485	337,205
Gross profit	469,269	451,194	443,659	435,804	447,457	428,067	430,336	430,696	1,799,926	1,736,556	1,657,829
Operating expenses
Sales and marketing	160,425	165,806	169,970	167,934	162,068	160,952	164,705	164,514	664,135	652,239	628,743
Research and development	95,078	94,061	91,056	85,889	85,479	88,602	89,234	87,050	366,084	350,365	334,227
General and administrative	41,748	39,374	39,276	39,984	37,832	39,368	38,009	41,678	160,382	156,887	138,431
Litigation expense	0	0	0	0	525	1	(135)	0	0	391	9,051
Restructuring charges	18,426	0	0	0	12,718	0	0	0	18,426	12,718	0
Total	315,677	299,241	300,302	293,807	298,622	288,923	291,813	293,242	1,209,027	1,172,600	1,110,452
Income from operations	153,592	151,953	143,357	141,997	148,835	139,144	138,523	137,454	590,899	563,956	547,377
Other income, net	5,667	2,259	2,790	2,145	5,027	2,589	1,302	2,643	12,861	11,561	2,514
Income before income taxes	159,259	154,212	146,147	144,142	153,862	141,733	139,825	140,097	603,760	575,517	549,891
Provision for income taxes	26,378	31,469	36,511	55,713	18,119	44,071	46,687	45,879	150,071	154,756	184,036
Net income	$ 132,881	$ 122,743	$ 109,636	$ 88,429	$ 135,743	$ 97,662	$ 93,138	$ 94,218	$ 453,689	$ 420,761	$ 365,855
Net income per share - basic (USD per share)	$ 2.20	$ 2.01	$ 1.79	$ 1.42	$ 2.15	$ 1.53	$ 1.44	$ 1.45	$ 7.41	$ 6.56	$ 5.43
Weighted average shares - basic (shares)	60,462	60,970	61,420	62,195	63,088	63,935	64,479	65,195	61,262	64,173	67,433
Net income per share - diluted (USD per share)	$ 2.18	$ 1.99	$ 1.77	$ 1.41	$ 2.14	$ 1.52	$ 1.43	$ 1.44	$ 7.32	$ 6.50	$ 5.38
Weighted average shares - diluted (shares)	61,070	61,633	62,059	62,550	63,446	64,361	65,028	65,645	62,013	64,775	67,984

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income Statement - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Net income	$ 453,689	$ 420,761	$ 365,855
Foreign currency translation adjustment	(1,415)	(3,671)	2,067
Unrealized (losses) gains on securities, net of taxes of $(869), $(493), and $14 for the years ended September 30, 2018, 2017, and 2016, respectively	(2,775)	(822)	23
Reclassification adjustment for realized losses (gains) included in net income, net of taxes of $(4), $186, and $(2) for the years ended September 30, 2018, 2017, and 2016, respectively	9	(310)	4
Net change in unrealized (losses) gains on available-for-sale securities, net of tax	(2,766)	(1,132)	27
Total other comprehensive (loss) income	(4,181)	(4,803)	2,094
Comprehensive income	$ 449,508	$ 415,958	$ 367,949

Consolidated Statements of Co_2

Consolidated Statements of Comprehensive Income (Parentheticals) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax	$ (869)	$ (493)	$ 14
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, Tax	$ (4)	$ 186	$ (2)

Consolidated Statement Of Share

Consolidated Statement Of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Accumulated Other Comprehensive Income/(Loss)	Retained Earnings
Balance, shares at Sep. 30, 2015		70,138,000
Balance at Sep. 30, 2015	$ 1,316,728	$ 10,159	$ (15,288)	$ 1,321,857
Exercise of employee stock options	179	$ 179
Exercise of employee stock options, shares		19,000
Issuance of stock under employee stock purchase plan	44,690	$ 44,690
Issuance of stock under employee stock purchase plan, shares		492,000
Issuance of restricted stock, shares		1,275,000
Repurchase of common stock	(700,124)	$ (197,677)		(502,447)
Repurchase of common stock, shares		(6,609,000)
Tax loss from employee stock transactions	(920)	$ (920)
Stock-based compensation	156,760	$ 156,760
Net income	365,855			365,855
Other comprehensive gain (loss)	2,094		2,094
Balance, shares at Sep. 30, 2016		65,315,000
Balance at Sep. 30, 2016	1,185,262	$ 13,191	(13,194)	1,185,265
Exercise of employee stock options	201	$ 201
Exercise of employee stock options, shares		9,000
Issuance of stock under employee stock purchase plan	46,838	$ 46,838
Issuance of stock under employee stock purchase plan, shares		469,000
Issuance of restricted stock, shares		1,362,000
Repurchase of common stock	(600,090)	$ (223,826)		(376,264)
Repurchase of common stock, shares		(4,561,000)
Tax benefit from employee stock transactions	5,897	$ 5,897
Stock-based compensation	175,326	$ 175,326
Net income	420,761			420,761
Other comprehensive gain (loss)	$ (4,803)		(4,803)
Balance, shares at Sep. 30, 2017	62,594,000	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	814	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	(4,074,170)	(4,074,000)
Stock-based compensation	$ 157,855	$ 157,855
Net income	453,689			453,689
Other comprehensive gain (loss)	$ (4,181)		(4,181)
Balance, shares at Sep. 30, 2018	60,215,000	60,215,000
Balance at Sep. 30, 2018	$ 1,285,492	$ 20,427	$ (22,178)	$ 1,287,243

Consolidated Statements Of Cash

Consolidated Statements Of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Operating activities
Net income	$ 453,689	$ 420,761	$ 365,855
Adjustments to reconcile net income to net cash provided by operating activities:
Realized (gain) loss on disposition of assets and investments	(267)	(439)	693
Stock-based compensation	157,855	175,326	156,760
Provisions for doubtful accounts and sales returns	1,461	366	1,526
Depreciation and amortization	59,491	61,148	56,776
Deferred income taxes	20,810	(4,626)	2,967
Changes in operating assets and liabilities:
Accounts receivable	(4,889)	(24,115)	9,732
Inventories	(734)	4,218	(334)
Other current assets	15,607	(14,890)	(1,876)
Other assets	446	(2,056)	(712)
Accounts payable and accrued liabilities	6,583	30,524	33,217
Deferred revenue	51,016	94,064	86,931
Net cash provided by operating activities	761,068	740,281	711,535
Investing activities
Purchases of investments	(855,424)	(446,838)	(354,708)
Maturities of investments	439,130	390,449	418,821
Sales of investments	12,736	66,858	66,848
Decrease (increase) in restricted cash	36	(73)	(3)
Acquisition of intangible assets	0	(4,000)	(4,750)
Cash provided by sale of fixed asset	1,000	0	0
Purchases of property and equipment	(53,465)	(38,681)	(63,488)
Net cash (used in) provided by investing activities	(455,987)	(32,285)	62,720
Financing activities
Excess tax benefit from stock-based compensation	0	7,019	2,608
Proceeds from the exercise of stock options and purchases of stock under employee stock purchase plan	48,818	47,039	44,869
Repurchase of common stock	(600,081)	(600,090)	(700,124)
Net cash used in financing activities	(551,263)	(546,032)	(652,647)
Net (decrease) increase in cash and cash equivalents	(246,182)	161,964	121,608
Effect of exchange rate changes on cash and cash equivalents	(2,339)	(3,307)	2,503
Cash and cash equivalents, beginning of year	673,228	514,571	390,460
Cash and cash equivalents, end of year	424,707	673,228	514,571
Supplemental disclosures of cash flow information
Cash paid for taxes	104,878	162,944	164,362
Other Significant Noncash Transaction, Value of Consideration Received	$ 9,958	$ 0	$ 0

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	12 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Summary Of Significant Accounting Policies	Summary of Significant Accounting Policies The Company F5 Networks, Inc. (the “Company”) is the leading developer and provider of application services. The Company’s core technology is a full-proxy, programmable, highly-scalable software platform called TMOS, which supports a broad array of features and functions designed to ensure that applications delivered over Internet Protocol (IP) networks are secure, fast, and available. The Company’s offerings include software products for local and global traffic management, network and application security, access management, web acceleration and a number of other network and application services. F5 offerings are available via software that can run individually or as part of an integrated solution on the Company’s high-performance, scalable, purpose-built BIG-IP appliances and VIPRION chassis-based hardware, as software-only Virtual Editions, or as software-based services available through a number of leading cloud marketplaces. The Company also offers distributed denial-of-service (DDoS) protection, application security and other application services by subscription on its cloud-based Silverline platform. In connection with its products, the Company offers a broad range of support and managed services including consulting, training, installation and maintenance. Accounting Principles The Company’s consolidated financial statements and accompanying notes are prepared on the accrual basis of accounting in accordance with generally accepted accounting principles in the United States of America (GAAP). Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation. Use of Estimates 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, disclosures of contingent assets and liabilities as of the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Estimates are used in accounting for revenue recognition, reserves for doubtful accounts, product returns, obsolete and excess inventory and valuation allowances on deferred tax assets. Actual results could differ from those estimates. Cash and Cash Equivalents 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. Investments The Company classifies its investment securities as available-for-sale. Investment securities, consisting of certificates of deposit, corporate and municipal bonds and notes, 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, 2018 , Synnex Corporation and Ingram Micro, Inc. accounted for 10.3% and 16.6% of the Company’s accounts receivable, respectively. At September 30, 2017 , Synnex Corporation and Arrow ECS, Inc. accounted for 13.6% 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, 2018 and 2017. 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). Inventories consist of the following (in thousands): September 30, 2018 2017 Finished goods $ 21,339 $ 20,280 Raw materials 9,229 9,554 $ 30,568 $ 29,834 Property and Equipment Property and equipment is 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 to five years. Leasehold improvements are amortized over the lesser of the remaining lease term or the estimated useful life of the improvements. The cost of normal maintenance and repairs is charged to expense as incurred and expenditures for major improvements are capitalized at cost. Gains or losses on the disposition of assets are reflected in the income statements at the time of disposal. Property and equipment consist of the following (in thousands): September 30, 2018 2017 Computer equipment $ 194,847 $ 177,235 Office furniture and equipment 31,625 32,781 Leasehold improvements 107,615 88,410 334,087 298,426 Accumulated depreciation and amortization (189,045 ) (176,006 ) $ 145,042 $ 122,420 Depreciation expense totaled approximately $45.9 million , $44.6 million , and $36.4 million for the fiscal years ended September 30, 2018 , 2017 and 2016 , respectively. 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. Goodwill was recorded in connection with various acquisitions in prior years. 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. As part of the annual goodwill impairment test, the Company has the option to perform a qualitative assessment to determine whether further impairment testing is necessary. Examples of events and circumstances that might indicate that the reporting unit’s fair value is less than its carrying amount include macro-economic conditions such as deterioration in the entity’s operating environment or industry or market considerations; entity-specific events such as increasing costs, declining financial performance, or loss of key personnel; or other events such as a sustained decrease in the stock price on either an absolute basis or relative to peers. If, as a result of its qualitative assessment, it is more-likely-than-not (i.e. greater than 50% chance) that the fair value of the Company’s reporting unit is less than its carrying amount, the quantitative impairment test will be required. Otherwise, no further testing will be required. If the Company chooses to bypass the qualitative assessment, it completes a quantitative assessment in performing its annual impairment test. As described in the "Recently Adopted Accounting Standards" section of Note 1, the Company elected to early adopt ASU 2017-04. For its annual impairment test performed in the second quarter of fiscal 2018, 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, 2018 and noted no indicators of impairment. Acquired Technology and Intangible Assets Acquired technology is recorded at cost and amortized over its estimated useful life. The estimated useful life of these assets is assessed and evaluated for reasonableness periodically. Acquired in-process research and development (IPR&D) are intangible assets initially recognized at fair value and classified as indefinite-lived assets until the successful completion or abandonment of the associated research and development efforts. During the development period, these assets will not be amortized as charges to earnings; instead these assets will be tested for impairment on an annual basis or more frequently if impairment indicators are identified. Amortization expense related to acquired technology totaled $7.4 million , $8.8 million and $10.6 million during the fiscal years 2018 , 2017 and 2016 , respectively, and is charged to cost of product revenues. The Company's intangible assets subject to amortization are amortized using the straight-line method over their estimated useful lives, ranging from three to ten years. The Company evaluates the recoverability of intangible assets periodically by taking into account events or circumstances that may warrant revised estimates of useful lives or that indicate the asset may be impaired. Amortization expense of all other intangible assets, including customer relationships, patents and trademarks was not material during the fiscal years 2018 , 2017 and 2016 . 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. Thereafter, software development costs incurred after the establishment of technological feasibility and prior to a product being released for sale are capitalized and reported at the lower of unamortized cost or net realizable value. Capitalized software development costs are amortized over the remaining estimated economic life of the product. The establishment of technological feasibility and the ongoing assessment of recoverability of costs require considerable judgment by the Company with respect to certain internal and external factors, including, but not limited to, anticipated future gross product revenues, estimated economic life and changes in hardware and software technology. The Company’s software development costs incurred subsequent to achieving technological feasibility have not been significant, and all software development costs have been expensed as research and development activities as incurred. Internal Use Software In accordance with the authoritative guidance, the Company capitalizes costs incurred during the application development stage associated with the development of new functionality for internal-use software and developed software related to the infrastructure of its SaaS-based product offerings. The capitalized costs are then amortized over the estimated useful life of the software, which is generally three to five years, and are included in property and equipment in the accompanying consolidated balance sheets. 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. No impairment of long-lived assets was noted as of and for the years ended September 30, 2018 , 2017 and 2016 . Revenue Recognition The Company sells products through distributors, resellers, and directly to end users. Revenue is recognized provided that all of the following criteria have been met: • Persuasive evidence of an arrangement exists. Evidence of an arrangement generally consists of a purchase order issued pursuant to the terms and conditions of a distributor, reseller or end user agreement. • Delivery has occurred. The Company uses shipping or related documents, or written evidence of customer acceptance, when applicable, to verify delivery or completion of any performance terms. • The sales price is fixed or determinable. The Company assesses whether the sales price is fixed or determinable based on payment terms associated with the transaction and whether the sales price is subject to refund or adjustment. • Collectability is reasonably assured. The Company assesses collectability primarily based on the creditworthiness of the customer as determined by credit checks and related analysis, as well as the Customer’s payment history. Revenue from the sale of products is generally recognized when the product has been shipped and the customer is obligated to pay for the product. When rights of return are present and the Company cannot estimate returns, revenue is recognized when such rights of return lapse. Payment terms to domestic customers are generally net 30 days to net 45 days. Payment terms to international customers range from net 30 days to net 120 days based on normal and customary trade practices in the individual markets. 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 when the consulting has been completed. Training revenue is recognized when the training has been completed. Arrangement consideration is first allocated between software (consisting of nonessential and stand-alone software) and non-software deliverables. The majority of the Company’s products are hardware appliances which contain software essential to the overall functionality of the products. Hardware appliances are generally sold with PCS and on occasion, with consulting and/or training services. Arrangement consideration in such multiple element transactions is allocated to each element based on a fair value hierarchy, where the selling price for an element is based on vendor specific objective evidence (VSOE), if available, third-party evidence (TPE), if available and VSOE is not available; or the best estimate of selling price (BESP), if neither VSOE or TPE is available. For software deliverables, the Company allocates revenue between multiple elements based on software revenue recognition guidance. Software revenue recognition guidance requires revenue earned on software arrangements involving multiple elements to be allocated to each element based on the relative fair values of those elements. The fair value of an element must be based on VSOE. Where VSOE of the fair value of delivered elements is not available, revenue is recognized on the “residual method” based on the fair value of undelivered elements. If evidence of fair value of one or more undelivered elements does not exist, all revenue is deferred and recognized at the earlier of the delivery of those elements or the establishment of fair value of the remaining undelivered elements. The Company establishes VSOE for its products, PCS, consulting and training services based on the sales price charged for each element when sold separately. The sales price is discounted from the applicable list price based on various factors including the type of customer, volume of sales, geographic region and program level. The Company’s list prices are generally not fair value as discounts may be given based on the factors enumerated above. The Company uses historical sales transactions to determine whether VSOE can be established for each of the elements. In most instances, VSOE of fair value is the sales price of actual standalone (unbundled) transactions within the past 12 month period, when a substantial majority of transactions (more than 80% ) are priced within a narrow range, which the Company has determined to be plus or minus 15% of the median sales price. The Company believes that the VSOE of fair value of training and consulting services is represented by the billable rate per hour, based on the rates charged to customers when they purchase standalone training or consulting services. The price of consulting services is not based on the type of customer, volume of sales, geographic region or program level. The Company is typically not able to determine VSOE or TPE for non-software products. TPE is determined based on competitor prices for similar elements when sold separately. Generally, the Company’s go-to-market strategy differs from that of other competitive products or services in its markets and the Company’s offerings contain a significant level of differentiation such that the comparable pricing of products with similar functionality cannot be obtained. Furthermore, the Company is unable to reliably determine the selling prices on a stand-alone basis of similar products offered by its competitors. When the Company is unable to establish selling price using VSOE or TPE, the Company uses BESP in its allocation of arrangement consideration. The objective of BESP is to determine the price at which the Company would transact a sale if the product or service were sold on a stand-alone basis. The Company has been able to establish BESP through the list price, less a discount deemed appropriate to maintain a reasonable gross margin. Management regularly reviews the gross margin information. Non-software product BESP is determined through the Company’s review of historical sales transactions within the past 12 month period. Additional factors considered in determining an appropriate BESP include, but are not limited to, cost of products, pricing practices, geographies, customer classes, and distribution channels. The Company regularly validates the VSOE of fair value and BESP for elements in its multiple element arrangements. The Company accounts for taxes collected from customers and remitted to governmental authorities on a net basis and excluded these amounts from revenues. 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, 2018 , 2017 and 2016 were not considered 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 and depreciation expense. Research and development expenses are reflected in the income statements as incurred. Advertising Advertising costs are expensed as incurred. The Company incurred $4.6 million , $3.5 million and $4.0 million in advertising costs during the fiscal years 2018 , 2017 and 2016 , 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. Foreign Currency The functional currency for the Company’s foreign subsidiaries is the local currency in which the respective entity is located, with the exception of F5 Networks Singapore Pte Ltd., F5 Networks (UK) Ltd., F5 Networks Benelux B.V. (Netherlands), F5 Networks Japan G.K., F5 Networks Canada Ltd., F5 Networks GmbH (Germany), F5 Networks Australia Pty, Ltd., F5 Networks (Israel) Ltd., Traffix Communication Systems Ltd. (Israel) and Versafe Ltd. (Israel), that use the U.S. dollar as their functional currency. 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 significant during the fiscal years ended September 30, 2018 , 2017 and 2016 . Segments Management has determined that the Company was organized as, and operated in, one reportable operating segment for fiscal year 2018 and prior years: 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 accounts for stock-based compensation using the straight-line attribution method for recognizing compensation expense. The Company recognized $157.9 million , $175.3 million and $156.8 million of stock-based compensation expense for the fiscal years ended September 30, 2018 , 2017 and 2016 , respectively. As of September 30, 2018 , there was $109.6 million of total unrecognized stock-based compensation cost, the majority of which will be recognized over the next 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. The Company issues incentive awards to its employees through stock-based compensation consisting of restricted stock units (RSUs). On October 31, 2018 , the Company’s Board of Directors and Compensation Committee approved 774,313 RSUs to employees and executive officers pursuant to the Company’s annual equity awards program. The value of RSUs is determined using the fair value method, which in this case, is based on the number of shares granted and the quoted price of the Company’s common stock on the date of grant. No stock options were granted in fiscal years 2018 , 2017 and 2016 . In determining the fair value of shares issued under the Employee Stock Purchase Plan (ESPP), the Company uses the Black-Scholes option pricing model that employs the following key assumptions. Employee Stock Purchase Plan 2018 2017 2016 Risk-free interest rate 2.25 % 1.14 % 0.44 % Expected dividend — — — Expected term 0.5 years 0.5 years 0.5 years Expected volatility 18.14 % 22.03 % 29.97 % The risk-free rate is based on the U.S. Treasury yield curve in effect at the time of grant. The Company does not anticipate declaring dividends in the foreseeable future. Expected volatility is based on the annualized daily historical volatility of the Company’s stock price commensurate with the expected life of the ESPP option. Expected term of the ESPP option is based on an offering period of six months. The assumptions above 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 recognizes compensation expense for only the portion of restricted stock units 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. Fifty percent of the aggregate number of RSUs issued to executive officers vest in equal quarterly increments, and 50% are subject to the Company achieving specified performance goals. For the prior year performance stock grants, 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 performance stock grants, 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 a 15% increase in annual stand-alone software revenue compared to the prior year; and (3) 25% of the annual performance stock grant is based on relative total shareholder return 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. As of September 30, 2018 , 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, 2017 140,135 Quarterly 4 years November 1, 2021 November 1, 2016 115,347 Quarterly 4 years November 1, 2020 November 2, 2015 145,508 Quarterly 4 years November 1, 2019 November 1, 2014 171,575 Quarterly 4 years November 1, 2018 The Company recognizes compensation costs 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. Common Stock Repurchase On October 25, 2017 , 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 $3.4 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 2018, the Company repurchased and retired 4,074,170 shares at an average price of $147.29 per share and as of September 30, 2018, the Company had $573.6 million remaining authorized to purchase shares. Earnings 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

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Sep. 30, 2018
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, 2018 , were as follows (in thousands): Fair Value Measurements at Reporting Date Using Fair Value at September 30, 2018 Quoted Prices in Active Markets for Identical Securities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash equivalents $ 41,468 $ 13,118 $ — $ 54,586 Short-term investments Available-for-sale securities — certificates of deposit — 2,970 — 2,970 Available-for-sale securities — corporate bonds and notes — 393,750 — 393,750 Available-for-sale securities — municipal bonds and notes — 22,524 — 22,524 Available-for-sale securities — U.S. government securities — 120,078 — 120,078 Available-for-sale securities — U.S. government agency securities — 75,383 — 75,383 Long-term investments Available-for-sale securities — corporate bonds and notes — 367,710 — 367,710 Available-for-sale securities — municipal bonds and notes — 24,286 — 24,286 Available-for-sale securities — U.S. government securities — 12,771 — 12,771 Available-for-sale securities — U.S. government agency securities — 6,417 — 6,417 Total $ 41,468 $ 1,039,007 $ — $ 1,080,475 The Company’s financial assets measured at fair value on a recurring basis subject to the disclosure requirements at September 30, 2017 , were as follows (in thousands): Fair Value Measurements at Reporting Date Using Fair Value at September 30, 2017 Quoted Prices in Active Markets for Identical Securities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash equivalents $ 13,967 $ 3,192 $ — $ 17,159 Short-term investments Available-for-sale securities — corporate bonds and notes — 172,493 — 172,493 Available-for-sale securities — municipal bonds and notes — 67,409 — 67,409 Available-for-sale securities — U.S. government securities — 72,930 — 72,930 Available-for-sale securities — U.S. government agency securities — 30,868 — 30,868 Long-term investments Available-for-sale securities — corporate bonds and notes — 191,782 — 191,782 Available-for-sale securities — municipal bonds and notes — 26,643 — 26,643 Available-for-sale securities — U.S. government securities — 29,374 — 29,374 Available-for-sale securities — U.S. government agency securities — 37,003 — 37,003 Total $ 13,967 $ 631,694 $ — $ 645,661 The Company uses the fair value hierarchy for financial assets and liabilities. 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, 2018 , the Company did not recognize any impairment charges related to goodwill, intangible assets, or long-lived assets. The carrying amounts of other current financial assets and other current financial liabilities approximate fair value due to their short-term nature.

Short-Term And Long-Term Invest

Short-Term And Long-Term Investments	12 Months Ended
	Sep. 30, 2018
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, 2018 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Certificates of deposit $ 2,970 $ — $ — $ 2,970 Corporate bonds and notes 394,684 9 (943 ) 393,750 Municipal bonds and notes 22,588 1 (65 ) 22,524 U.S. government securities 120,283 — (205 ) 120,078 U.S. government agency securities 75,587 — (204 ) 75,383 $ 616,112 $ 10 $ (1,417 ) $ 614,705 September 30, 2017 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate bonds and notes $ 172,560 $ 25 $ (92 ) $ 172,493 Municipal bonds and notes 67,382 36 (9 ) 67,409 U.S. government securities 72,991 — (61 ) 72,930 U.S. government agency securities 30,954 — (86 ) 30,868 $ 343,887 $ 61 $ (248 ) $ 343,700 Long-term investments consist of the following (in thousands): September 30, 2018 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate bonds and notes $ 370,377 $ 25 $ (2,692 ) $ 367,710 Municipal bonds and notes 24,468 — (182 ) 24,286 U.S. government securities 12,956 — (185 ) 12,771 U.S. government agency securities 6,500 — (83 ) 6,417 $ 414,301 $ 25 $ (3,142 ) $ 411,184 September 30, 2017 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate bonds and notes $ 192,278 $ 25 $ (521 ) $ 191,782 Municipal bonds and notes 26,639 46 (42 ) 26,643 U.S. government securities 29,427 — (53 ) 29,374 U.S. government agency securities 37,164 — (161 ) 37,003 $ 285,508 $ 71 $ (777 ) $ 284,802 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, 2018 (in thousands): Less Than 12 Months 12 Months or Greater Total September 30, 2018 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Corporate bonds and notes $ 543,729 $ (1,800 ) $ 152,097 $ (1,835 ) $ 695,826 $ (3,635 ) Municipal bonds and notes 26,846 (123 ) 14,363 (124 ) 41,209 (247 ) U.S. government securities 103,470 (281 ) 29,379 (109 ) 132,849 (390 ) U.S. government agency securities 44,812 (110 ) 36,987 (177 ) 81,799 (287 ) Total $ 718,857 $ (2,314 ) $ 232,826 $ (2,245 ) $ 951,683 $ (4,559 ) 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, 2017 (in thousands): Less Than 12 Months 12 Months or Greater Total September 30, 2017 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Corporate bonds and notes $ 262,852 $ (528 ) $ 35,401 $ (85 ) $ 298,253 $ (613 ) Municipal bonds and notes 30,256 (49 ) 881 (2 ) 31,137 (51 ) U.S. government securities 94,312 (105 ) 7,992 (9 ) 102,304 (114 ) U.S. government agency securities 36,121 (83 ) 31,750 (164 ) 67,871 (247 ) Total $ 423,541 $ (765 ) $ 76,024 $ (260 ) $ 499,565 $ (1,025 ) The Company invests in securities that are rated investment grade or better. The unrealized losses on investments for fiscal year 2018 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, 2018 , there were no investments in its portfolio that were other-than-temporarily impaired.

Balance Sheet Details

Balance Sheet Details	12 Months Ended
	Sep. 30, 2018
Balance Sheet Details [Abstract]
Balance Sheet Details	Balance Sheet Details Goodwill There was no change in the carrying amount of goodwill during fiscal years 2018 and 2017 . Other Assets Other assets consist of the following (in thousands): September 30, 2018 2017 Acquired and developed technology and software development costs $ 17,641 $ 25,085 Intangible assets 13,618 17,469 Restricted cash and deposits 10,927 11,221 $ 42,186 $ 53,775 Amortization expense related to other assets was approximately $11.1 million , $12.3 million , and $13.9 million for the fiscal years ended September 30, 2018 , 2017 and 2016 , respectively. Intangible assets are included in other assets on the balance sheet and consist of the following (in thousands): 2018 2017 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Acquired and developed technology and software development costs $ 63,672 $ (46,031 ) $ 17,641 $ 69,307 $ (44,222 ) $ 25,085 Customer relationships 8,242 (4,376 ) 3,866 8,242 (3,552 ) 4,690 Patents and trademarks 18,971 (9,219 ) 9,752 19,756 (7,159 ) 12,597 Trade names 973 (973 ) — 973 (791 ) 182 Non-compete covenants 1,960 (1,960 ) — 2,532 (2,532 ) — $ 93,818 $ (62,559 ) $ 31,259 $ 100,810 $ (58,256 ) $ 42,554 Estimated amortization expense for intangible assets for the five succeeding fiscal years is as follows (in thousands): 2019 $ 6,858 2020 6,363 2021 6,232 2022 5,026 2023 4,229 $ 28,708 Accrued Liabilities Accrued liabilities consist of the following (in thousands): September 30, 2018 2017 Payroll and benefits $ 104,815 $ 109,088 Sales and marketing 2,743 6,654 Restructuring 8,268 7,741 Income tax accruals 17,795 15,519 Other tax accruals 9,861 13,429 Other 37,497 34,948 $ 180,979 $ 187,379

Income Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2018
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, 2018 2017 2016 United States $ 441,336 $ 452,869 $ 465,738 International 162,424 122,648 84,153 $ 603,760 $ 575,517 $ 549,891 The provision for income taxes (benefit) consists of the following (in thousands): Years Ended September 30, 2018 2017 2016 Current U.S. federal $ 78,454 $ 113,105 $ 129,728 State 9,800 10,381 16,821 Foreign 41,040 34,679 31,015 Total 129,294 158,165 177,564 Deferred U.S. federal 21,259 964 9,770 State 725 99 (1,029 ) Foreign (1,207 ) (4,472 ) (2,269 ) Total 20,777 (3,409 ) 6,472 $ 150,071 $ 154,756 $ 184,036 The effective tax rate differs from the U.S. federal statutory rate as follows (in thousands): Years Ended September 30, 2018 2017 2016 Income tax provision at statutory rate $ 147,921 $ 201,431 $ 192,462 State taxes, net of federal benefit 9,349 9,235 13,434 Foreign operations (6,696 ) (40,606 ) (9,199 ) Research and development and other credits (13,159 ) (12,795 ) (18,368 ) Domestic manufacturing deduction (9,722 ) (15,802 ) (14,624 ) Stock-based and other compensation (150 ) 12,688 17,137 Impacts of the Tax Cuts and Jobs Act 21,015 — — Other 1,513 605 3,194 $ 150,071 $ 154,756 $ 184,036 The provision for income taxes for fiscal year 2018 includes various impacts from the Tax Cuts and Jobs Act enacted on December 22, 2017. Significant impacts include a reduction of the U.S. federal income tax rate from 35% to 24.5% , partially offset with a $7.0 million provisional tax expense for the deemed repatriation of undistributed foreign earnings, and a $14.0 million 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. Several provisions of the Tax Cuts and Jobs Act are not effective for the Company until fiscal year 2019, including a further reduction in the U.S. federal income tax rate to 21%, a deduction for foreign derived intangible income, repeal of the deduction for income attributable to domestic production activities, and a tax on global intangible low-taxed income (GILTI). The Company has made an accounting policy election to treat taxes under the GILTI provision as a current period expense. During the year ended September 30, 2017, the Company recorded a $21.0 million reduction to tax expense related to the utilization of U.S. foreign tax credits. This non-recurring reduction to tax expense is presented as part of foreign operations in the Company's effective tax rate reconciliation. Effective January 1, 2018, the new U.S. tax law provides a deduction for the foreign-source portion of dividends received from specified foreign corporations. As of September 30, 2018, the Company does not maintain an indefinite reinvestment assertion on any 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 accordance with SEC Staff Accounting Bulletin (“SAB”) No. 118, the Company recorded a provisional tax expense of $7.0 million related to the deemed repatriation of undistributed foreign earnings in the period ended December 31, 2017. The Company did not record any adjustments to the provisional tax expense in the period ended September 30, 2018. Additional regulatory guidance may result in a change to the provisional amount. SAB No. 118 provides a one-year measurement period to complete the accounting. The Company benefits from a tax incentive arrangement in a foreign jurisdiction, which is effective through March 31, 2021. The tax incentive agreement is conditional upon meeting certain employment and investment thresholds. This arrangement decreased foreign taxes by $6.4 million and $6.9 million , and increased diluted earnings per common share by $0.10 and $0.11 for the years ended September 30, 2018 and 2017, 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, 2018 2017 Deferred tax assets Net operating loss carry-forwards $ 11,540 $ 11,235 Allowance for doubtful accounts 368 1,236 Accrued compensation and benefits 8,202 11,617 Inventories and related reserves 324 715 Stock-based compensation 5,570 11,857 Deferred revenue 29,290 43,371 Other accruals and reserves 14,409 17,924 Tax credit carryforwards 12,177 7,873 Depreciation 671 628 82,551 106,456 Valuation allowance (22,780 ) (18,189 ) 59,771 88,267 Deferred tax liabilities Purchased intangibles and other (10,678 ) (17,459 ) Depreciation (12,277 ) (16,893 ) Other accruals and reserves (3,410 ) (676 ) (26,365 ) (35,028 ) Net deferred tax assets $ 33,406 $ 53,239 At September 30, 2018 , the Company had foreign net operating loss carry-forwards of approximately $58.4 million that can be carried forward indefinitely and $4.1 million that will expire in fiscal years 2026 to 2028. In addition, there are $8.2 million of state tax credit carryforwards that can be carried forward indefinitely and $3.6 million that will expire in fiscal years 2028 to 2033. Management believes that it is more-likely-than-not that the benefit from certain foreign net operating loss carryforwards and state tax 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 $4.6 million and $3.9 million for the years ended September 30, 2018 and 2017 , 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 2018 , 2017 and 2016 (in thousands): 2018 2017 2016 Balance, beginning of period $ 23,135 $ 13,687 $ 9,562 Gross increases related to prior period tax positions 2,715 2,769 1,622 Gross decreases related to prior period tax positions — — (7 ) Gross increases related to current period tax positions 8,230 8,507 4,441 Decreases relating to settlements with tax authorities — (240 ) (521 ) Reductions due to lapses of statute of limitations (2,408 ) (1,588 ) (1,410 ) Balance, end of period $ 31,672 $ 23,135 $ 13,687 The total amount of gross unrecognized tax benefits was $31.7 million , $23.1 million , and $13.7 million as of September 30, 2018 , 2017 , and 2016 , respectively, of which, $23.1 million , $18.3 million , and $11.1 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, 2018 , 2017 and 2016 , the Company recorded approximately $437,000 , $258,000 and $18,000 , respectively, of interest and penalty expense related to uncertain tax positions. As of September 30, 2018 and 2017 , the Company had a cumulative balance of accrued interest and penalties on unrecognized tax positions of $1,615,000 and $1,178,000 , 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, 2014 . The Company is currently under audit by the IRS for fiscal year 2016 and various states for fiscal years 2014 through 2017. Major jurisdictions where there are wholly owned subsidiaries of F5 Networks, Inc. which require income tax filings include the United Kingdom, Japan, Singapore, and Australia. The earliest periods open for review by local taxing authorities are fiscal years 2017 for the United Kingdom, 2012 for Japan, 2013 for Singapore, and 2014 for Australia. Within the next four fiscal quarters, the statute of limitations will begin to close on the fiscal year 2015 federal income tax return, fiscal years 2014 and 2015 state income tax returns, and fiscal years 2012 to 2017 foreign income tax returns.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Sep. 30, 2018
Share-based Compensation [Abstract]
Stock-Based Compensation	Stock-based Compensation The majority of awards consist of restricted stock units and to a lesser degree, stock options. Employees vest in restricted stock units and stock options ratably over the corresponding service term, generally one to four years. The Company’s stock options expire ten years from the date of grant. Restricted stock units are payable in shares of the Company’s common stock as the periodic vesting requirements are satisfied. The value of a restricted stock unit is based upon the fair market value of the Company’s common stock on the date of grant. The value of restricted stock units is determined using the intrinsic value method and is based on the number of shares granted and the quoted price of the Company’s common stock on the date of grant. Alternatively, the Company used the Black-Scholes option pricing model to determine the fair value of its stock options. Compensation expense related to restricted stock units and stock options is recognized over the vesting period. The 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 8,000,000 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, 2018 there were 652,351 shares available for awards under the Employee Stock Purchase Plan. 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 2018 , the Company issued no stock options or restricted stock units under the Traffix Plan. As of September 30, 2018 , 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 connection with the Company’s acquisition of Defense.Net, Inc. in the third quarter of fiscal year 2014, the Company assumed the Defense.Net, Inc. 2012 Stock Option and Grant Plan, or the Defense.Net Plan. Unvested options to acquire Defense.Net's common stock were converted into options to acquire the Company’s common stock in connection with the acquisition. A total of 84,375 shares of common stock were reserved for issuance under the Defense.Net Plan. The plan provided for grants of stock options to persons who were employees, officers, directors, consultants or advisors to Defense.Net, Inc. on or prior to May 22, 2014. During the fiscal year 2018 , the Company issued no stock options or restricted stock units under the Defense.Net Plan. As of September 30, 2018 , there were options to purchase 113 shares outstanding and no shares available for additional awards under the Defense.Net Plan. The Company terminated the Defense.Net Plan effective January 5, 2015 and no additional shares may be issued from the Defense.Net Plan. 2014 Incentive Plan. In March 2014, the Company adopted the 2014 Incentive Plan, or the 2014 Plan, which amended and restated the 2005 Equity Incentive Plan. The 2014 Plan provides for discretionary grants of non-statutory stock options and stock units for employees, including officers, and other service providers. A total of 18,730,000 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 2018 , the Company issued no stock options, 62,396 performance stock units and 1,307,589 restricted stock units under the 2014 Plan. As of September 30, 2018 , there were no options outstanding, 24,079 performance stock units outstanding, 1,150,870 restricted stock units outstanding and 2,051,687 shares available for new awards under the 2014 Plan. A majority of the restricted stock units the Company grants to its employees vest quarterly over a two -year period. The performance stock units and restricted stock units under all plans were granted during fiscal years 2018 , 2017 and 2016 with a per-share weighted average fair value of $126.86 , $134.35 and $109.65 , respectively. The fair value of performance stock units and restricted stock units vested during fiscal years 2018 , 2017 and 2016 was $182.6 million , $176.8 million and $137.7 million , respectively. A summary of restricted stock unit activity under the 2014 Plan is as follows: Performance Stock Units Restricted Stock Units Outstanding Performance Stock Units Weighted Average Grant Date Fair Value Outstanding Restricted Stock Units Weighted Average Grant Date Fair Value Balance, September 30, 2017 13,871 $ 121.44 1,347,431 $ 127.89 Units granted 62,396 118.97 1,307,589 127.24 Units vested (24,374 ) 145.23 (1,191,577 ) 150.75 Units cancelled (27,814 ) 119.15 (312,573 ) 125.46 Balance, September 30, 2018 24,079 $ 119.01 1,150,870 $ 129.35 A summary of stock option activity under all of the Company’s plans is as follows: Options Outstanding Number of Shares Weighted Average Exercise Price per Share Balance, September 30, 2017 976 $ 3.18 Options granted — — Options exercised (814 ) 3.07 Options cancelled — — Balance, September 30, 2018 162 $ 3.76 No stock options were granted in fiscal years 2018 , 2017 and 2016 . The total intrinsic value of options exercised during fiscal 2018 , 2017 and 2016 was $0.1 million , $1.0 million and $1.9 million , respectively. Number of Shares Weighted Average Remaining Contractual Life (in Years) Weighted Average Exercise Price per Share Aggregate Intrinsic Value(1) (In thousands) Stock options outstanding 162 4.73 $ 3.76 $ 32 Exercisable 162 4.73 $ 3.76 $ 32 Vested and expected to vest 162 4.73 $ 3.76 $ 32 (1) Aggregate intrinsic value represents the difference between the fair value of the Company’s common stock underlying these options at September 30, 2018 and the related exercise prices. As of September 30, 2018 , equity based awards (including stock options and restricted stock units) are available for future issuance as follows: Awards Available for Grant Balance, September 30, 2017 3,081,285 Granted (1,369,985 ) Cancelled 341,000 Additional shares reserved (terminated), net (613 ) Balance, September 30, 2018 2,051,687

Commitments And Contingencies

Commitments And Contingencies	12 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Commitments And Contingencies	Commitments and Contingencies Operating Leases The majority of the Company’s operating lease payments relate to the Company’s four building corporate headquarters in Seattle, Washington. The leases for all four buildings will expire in 2022 . The Company also leases additional office space for product development and sales and support personnel in the United States and internationally. In October 2006, the Company entered into an agreement to lease a total of approximately 137,000 square feet of office space in a building known as 333 Elliott West, which is adjacent to the four buildings that serve as the Company’s corporate headquarters. The lease expired in May of 2018 . On May 3, 2017, the Company entered into an agreement to lease approximately 515,000 square feet of office space in Seattle, Washington that will serve as its new corporate headquarters. The initial term of the lease is 14.5 years and is expected to commence on the latter of (i) April 1, 2019 or (ii) 10 months after the substantial completion date of the construction of the Premises. This lease will expire in 2033 with an option for renewal. Future minimum operating lease payments, net of sublease income, are as follows (in thousands): Gross Lease Payments Sublease Income Net Lease Payments 2019 30,870 — 30,870 2020 45,418 — 45,418 2021 42,615 — 42,615 2022 40,285 — 40,285 2023 31,238 — 31,238 Thereafter 271,882 — 271,882 $ 462,308 $ — $ 462,308 Rent expense under non-cancelable operating leases amounted to approximately $30.0 million , $30.2 million , and $30.1 million for the fiscal years ended September 30, 2018 , 2017 , and 2016 , respectively. 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, 2018 , the Company’s remaining unfulfilled purchase obligations were $26.2 million . Litigation On April 4, 2016, the Company sued Radware, Inc. in the United States District Court for the Western District of Washington (the case was subsequently moved to the Northern District of California) accusing Radware of infringing three Company patents. The Company’s complaint seeks a jury trial and an unspecified amount of monetary damages, as well as interest, costs, and injunctive relief. Radware moved to dismiss the allegations of one patent but the motion was denied. Radware filed a counterclaim separately asserting that the Company is infringing U.S. patent no. 9,231,853, an expired ISP link load balancing patent related to the patents previously asserted by Radware in litigation in California that has been completed. Radware claims that the Company's BIG-IP product infringes. The counterclaim seeks injunctive relief and unspecified damages. The Company denied infringement and asserted that the '853 patent is invalid. Both parties filed inter partes reviews (IPRs) on the patents asserted against them. All of Radware's IPRs were denied and the Company’s IPR against the ‘853 patent resulted in cancellation of all but four of the ‘853 claims. The Court has entered a schedule for trial in November of 2019. Both parties moved for summary judgment on the issue of infringement with respect to the ‘853 patent. A hearing on the motions was conducted on November 15, 2018 and the Court granted F5's summary judgment motion for noninfringement by order dated November 19, 2018. Accordingly, the case will proceed solely on F5's infringement claims against Radware. In addition to the above referenced matters, the Company is subject to other legal proceedings, claims, and litigation arising in the ordinary course of business. 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, 2018
Restructuring and Related Activities [Abstract]
Restructuring Charges	Restructuring Charges In July 2018, 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 215 employees. The Company recorded a restructuring charge of $18.4 million in the fourth quarter of fiscal 2018. The Company does not expect to record any significant future charges related to the restructuring plan. During the year ended September 30, 2018, the following activity was recorded (in thousands): Employee Severance, Benefits and Related Costs Accrued expenses, October 1, 2017 $ 7,741 Restructuring charges 18,426 Cash payments (17,899 ) Non-cash items — Accrued expenses, September 30, 2018 $ 8,268

Employee Benefit Plans

Employee Benefit Plans	12 Months Ended
	Sep. 30, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Employee Benefit Plans	Employee Benefit Plans The 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, 2018 , 2017 , and 2016 were approximately $10.5 million , $10.5 million and $9.5 million , respectively. Contributions made by the Company vest over four years.

Geographic Sales And Significan

Geographic Sales And Significant Customers	12 Months Ended
	Sep. 30, 2018
Segments, Geographical Areas [Abstract]
Geographic Sales And Significant Customers	Geographic Sales and Significant Customers 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. The Company does business in four main geographic regions: the Americas (primarily the United States); Europe, the Middle East, and Africa (EMEA); Japan; and the Asia Pacific region (APAC). The Company’s chief operating decision-making group 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, 2018 2017 2016 Americas: United States $ 1,088,270 $ 1,075,222 $ 1,019,054 Other 116,073 110,298 106,228 Total Americas 1,204,343 1,185,520 1,125,282 EMEA 546,239 506,571 487,966 Japan 95,251 95,055 94,767 Asia Pacific 315,574 302,895 287,019 $ 2,161,407 $ 2,090,041 $ 1,995,034 The following distributors of the Company's products accounted for more than 10% of total net revenue: Years Ended September 30, 2018 2017 2016 Ingram Micro, Inc. 16.6 % 16.1 % 14.9 % Tech Data 1 11.6 % 12.4 % 13.3 % Synnex Corporation 2 10.8 % — — Arrow ECS 10.7 % 10.4 % 10.1 % Westcon Group, Inc. 2 10.4 % 17.7 % 18.7 % (1) On February 27, 2017, Tech Data completed the acquisition of Avnet Technology Solutions. Revenues for the year ended September 30, 2017 represent combined revenues for Tech Data and Avnet while revenues for years ended September 30, 2016 and 2015 represent revenues from Avnet only. (2) On September 1, 2017, Synnex Corporation completed the acquisition of Westcon Americas. The Company tracks assets by physical location. Long-lived assets consist of property and equipment, net, and are shown below (in thousands): September 30, 2018 2017 United States $ 126,790 $ 103,486 EMEA 12,538 15,054 Other countries 5,714 3,880 $ 145,042 $ 122,420

Quarterly Results Of Operations

Quarterly Results Of Operations (Unaudited)	12 Months Ended
	Sep. 30, 2018
Quarterly Financial Data [Abstract]
Quarterly Results Of Operations	Quarterly Results of Operations (Unaudited) The following presents the Company’s unaudited quarterly results of operations for the eight quarters ended September 30, 2018 . 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, 2018 June 30, 2018 March 31, 2018 Dec. 31, 2017 Sept. 30, 2017 June 30, 2017 March 31, 2017 Dec. 31, 2016 (unaudited and in thousands, except per share data) Net revenues Products $ 256,412 $ 238,835 $ 237,558 $ 227,303 $ 248,990 $ 235,109 $ 241,080 $ 239,483 Services 306,297 303,368 295,746 295,888 289,008 282,728 277,168 276,475 Total 562,709 542,203 533,304 523,191 537,998 517,837 518,248 515,958 Cost of net revenues Products 48,505 45,164 44,127 43,265 46,641 43,787 43,928 41,676 Services 44,935 45,845 45,518 44,122 43,900 45,983 43,984 43,586 Total 93,440 91,009 89,645 87,387 90,541 89,770 87,912 85,262 Gross profit 469,269 451,194 443,659 435,804 447,457 428,067 430,336 430,696 Operating expenses Sales and marketing 160,425 165,806 169,970 167,934 162,068 160,952 164,705 164,514 Research and development 95,078 94,061 91,056 85,889 85,479 88,602 89,234 87,050 General and administrative 41,748 39,374 39,276 39,984 37,832 39,368 38,009 41,678 Litigation expense — — — — 525 1 (135 ) — Restructuring charges 18,426 — — — 12,718 — — — Total operating expenses 315,677 299,241 300,302 293,807 298,622 288,923 291,813 293,242 Income from operations 153,592 151,953 143,357 141,997 148,835 139,144 138,523 137,454 Other income, net 5,667 2,259 2,790 2,145 5,027 2,589 1,302 2,643 Income before income taxes 159,259 154,212 146,147 144,142 153,862 141,733 139,825 140,097 Provision for income taxes 26,378 31,469 36,511 55,713 18,119 44,071 46,687 45,879 Net income $ 132,881 $ 122,743 $ 109,636 $ 88,429 $ 135,743 $ 97,662 $ 93,138 $ 94,218 Net income per share — basic $ 2.20 $ 2.01 $ 1.79 $ 1.42 $ 2.15 $ 1.53 $ 1.44 $ 1.45 Weighted average shares — basic 60,462 60,970 61,420 62,195 63,088 63,935 64,479 65,195 Net income per share — diluted $ 2.18 $ 1.99 $ 1.77 $ 1.41 $ 2.14 $ 1.52 $ 1.43 $ 1.44 Weighted average shares — diluted 61,070 61,633 62,059 62,550 63,446 64,361 65,028 65,645

Subsequent Events

Subsequent Events	12 Months Ended
	Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On October 31, 2018, the Company's Board of Directors authorized an additional $1.0 billion for its common stock share repurchase program. This new authorization is incremental to the $573.6 million currently unused in the existing program, which was initially approved in October 2010. Acquisitions for the share repurchase program will be made from time to time in private transactions or open market purchases as permitted by securities laws and other legal requirements. The timing and amounts of any purchases will be based on market conditions and other factors including but not limited to price, regulatory requirements and capital availability. The program does not require the purchase of any minimum number of shares and the program may be modified, suspended or discontinued at any time.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policy)	12 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Accounting Principles	Accounting Principles The Company’s consolidated financial statements and accompanying notes are prepared on the accrual basis of accounting in accordance with generally accepted accounting principles in the United States of America (GAAP).
Principles Of Consolidation	Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.
Use Of Estimates	Use of Estimates 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, disclosures of contingent assets and liabilities as of the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Estimates are used in accounting for revenue recognition, reserves for doubtful accounts, product returns, obsolete and excess inventory and valuation allowances on deferred tax assets. Actual results could differ from those estimates.
Cash And Cash Equivalents	Cash and Cash Equivalents 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.
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, 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, 2018 , Synnex Corporation and Ingram Micro, Inc. accounted for 10.3% and 16.6% of the Company’s accounts receivable, respectively. At September 30, 2017 , Synnex Corporation and Arrow ECS, Inc. accounted for 13.6% 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, 2018 and 2017. 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 is 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 to five years. Leasehold improvements are amortized over the lesser of the remaining lease term or the estimated useful life of the improvements. The cost of normal maintenance and repairs is charged to expense as incurred and expenditures for major improvements are capitalized at cost. Gains or losses on the disposition of assets are reflected in the income statements at the time of disposal.
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. Goodwill was recorded in connection with various acquisitions in prior years. 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. As part of the annual goodwill impairment test, the Company has the option to perform a qualitative assessment to determine whether further impairment testing is necessary. Examples of events and circumstances that might indicate that the reporting unit’s fair value is less than its carrying amount include macro-economic conditions such as deterioration in the entity’s operating environment or industry or market considerations; entity-specific events such as increasing costs, declining financial performance, or loss of key personnel; or other events such as a sustained decrease in the stock price on either an absolute basis or relative to peers. If, as a result of its qualitative assessment, it is more-likely-than-not (i.e. greater than 50% chance) that the fair value of the Company’s reporting unit is less than its carrying amount, the quantitative impairment test will be required. Otherwise, no further testing will be required. If the Company chooses to bypass the qualitative assessment, it completes a quantitative assessment in performing its annual impairment test. As described in the "Recently Adopted Accounting Standards" section of Note 1, the Company elected to early adopt ASU 2017-04. For its annual impairment test performed in the second quarter of fiscal 2018, 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, 2018 and noted no indicators of impairment.
Acquired Technology and Intangible Assets	Acquired Technology and Intangible Assets Acquired technology is recorded at cost and amortized over its estimated useful life. The estimated useful life of these assets is assessed and evaluated for reasonableness periodically. Acquired in-process research and development (IPR&D) are intangible assets initially recognized at fair value and classified as indefinite-lived assets until the successful completion or abandonment of the associated research and development efforts. During the development period, these assets will not be amortized as charges to earnings; instead these assets will be tested for impairment on an annual basis or more frequently if impairment indicators are identified. Amortization expense related to acquired technology totaled $7.4 million , $8.8 million and $10.6 million during the fiscal years 2018 , 2017 and 2016 , respectively, and is charged to cost of product revenues. The Company's intangible assets subject to amortization are amortized using the straight-line method over their estimated useful lives, ranging from three to ten years. The Company evaluates the recoverability of intangible assets periodically by taking into account events or circumstances that may warrant revised estimates of useful lives or that indicate the asset may be impaired. Amortization expense of all other intangible assets, including customer relationships, patents and trademarks was not material during the fiscal years 2018 , 2017 and 2016 .
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. Thereafter, software development costs incurred after the establishment of technological feasibility and prior to a product being released for sale are capitalized and reported at the lower of unamortized cost or net realizable value. Capitalized software development costs are amortized over the remaining estimated economic life of the product. The establishment of technological feasibility and the ongoing assessment of recoverability of costs require considerable judgment by the Company with respect to certain internal and external factors, including, but not limited to, anticipated future gross product revenues, estimated economic life and changes in hardware and software technology. The Company’s software development costs incurred subsequent to achieving technological feasibility have not been significant, and all software development costs have been expensed as research and development activities as incurred.
Internal Use Software	Internal Use Software In accordance with the authoritative guidance, the Company capitalizes costs incurred during the application development stage associated with the development of new functionality for internal-use software and developed software related to the infrastructure of its SaaS-based product offerings. The capitalized costs are then amortized over the estimated useful life of the software, which is generally three to five years, and are included in property and equipment in the accompanying consolidated balance sheets.
Impairment Of Long-Lived Assets	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. No impairment of long-lived assets was noted as of and for the years ended September 30, 2018 , 2017 and 2016 .
Revenue Recognition	Revenue Recognition The Company sells products through distributors, resellers, and directly to end users. Revenue is recognized provided that all of the following criteria have been met: • Persuasive evidence of an arrangement exists. Evidence of an arrangement generally consists of a purchase order issued pursuant to the terms and conditions of a distributor, reseller or end user agreement. • Delivery has occurred. The Company uses shipping or related documents, or written evidence of customer acceptance, when applicable, to verify delivery or completion of any performance terms. • The sales price is fixed or determinable. The Company assesses whether the sales price is fixed or determinable based on payment terms associated with the transaction and whether the sales price is subject to refund or adjustment. • Collectability is reasonably assured. The Company assesses collectability primarily based on the creditworthiness of the customer as determined by credit checks and related analysis, as well as the Customer’s payment history. Revenue from the sale of products is generally recognized when the product has been shipped and the customer is obligated to pay for the product. When rights of return are present and the Company cannot estimate returns, revenue is recognized when such rights of return lapse. Payment terms to domestic customers are generally net 30 days to net 45 days. Payment terms to international customers range from net 30 days to net 120 days based on normal and customary trade practices in the individual markets. 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 when the consulting has been completed. Training revenue is recognized when the training has been completed. Arrangement consideration is first allocated between software (consisting of nonessential and stand-alone software) and non-software deliverables. The majority of the Company’s products are hardware appliances which contain software essential to the overall functionality of the products. Hardware appliances are generally sold with PCS and on occasion, with consulting and/or training services. Arrangement consideration in such multiple element transactions is allocated to each element based on a fair value hierarchy, where the selling price for an element is based on vendor specific objective evidence (VSOE), if available, third-party evidence (TPE), if available and VSOE is not available; or the best estimate of selling price (BESP), if neither VSOE or TPE is available. For software deliverables, the Company allocates revenue between multiple elements based on software revenue recognition guidance. Software revenue recognition guidance requires revenue earned on software arrangements involving multiple elements to be allocated to each element based on the relative fair values of those elements. The fair value of an element must be based on VSOE. Where VSOE of the fair value of delivered elements is not available, revenue is recognized on the “residual method” based on the fair value of undelivered elements. If evidence of fair value of one or more undelivered elements does not exist, all revenue is deferred and recognized at the earlier of the delivery of those elements or the establishment of fair value of the remaining undelivered elements. The Company establishes VSOE for its products, PCS, consulting and training services based on the sales price charged for each element when sold separately. The sales price is discounted from the applicable list price based on various factors including the type of customer, volume of sales, geographic region and program level. The Company’s list prices are generally not fair value as discounts may be given based on the factors enumerated above. The Company uses historical sales transactions to determine whether VSOE can be established for each of the elements. In most instances, VSOE of fair value is the sales price of actual standalone (unbundled) transactions within the past 12 month period, when a substantial majority of transactions (more than 80% ) are priced within a narrow range, which the Company has determined to be plus or minus 15% of the median sales price. The Company believes that the VSOE of fair value of training and consulting services is represented by the billable rate per hour, based on the rates charged to customers when they purchase standalone training or consulting services. The price of consulting services is not based on the type of customer, volume of sales, geographic region or program level. The Company is typically not able to determine VSOE or TPE for non-software products. TPE is determined based on competitor prices for similar elements when sold separately. Generally, the Company’s go-to-market strategy differs from that of other competitive products or services in its markets and the Company’s offerings contain a significant level of differentiation such that the comparable pricing of products with similar functionality cannot be obtained. Furthermore, the Company is unable to reliably determine the selling prices on a stand-alone basis of similar products offered by its competitors. When the Company is unable to establish selling price using VSOE or TPE, the Company uses BESP in its allocation of arrangement consideration. The objective of BESP is to determine the price at which the Company would transact a sale if the product or service were sold on a stand-alone basis. The Company has been able to establish BESP through the list price, less a discount deemed appropriate to maintain a reasonable gross margin. Management regularly reviews the gross margin information. Non-software product BESP is determined through the Company’s review of historical sales transactions within the past 12 month period. Additional factors considered in determining an appropriate BESP include, but are not limited to, cost of products, pricing practices, geographies, customer classes, and distribution channels. The Company regularly validates the VSOE of fair value and BESP for elements in its multiple element arrangements. The Company accounts for taxes collected from customers and remitted to governmental authorities on a net basis and excluded these amounts from revenues.
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, 2018 , 2017 and 2016 were not considered 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 and depreciation expense. Research and development expenses are reflected in the income statements as incurred.
Advertising	Advertising Advertising costs are expensed as incurred. The Company incurred $4.6 million , $3.5 million and $4.0 million in advertising costs during the fiscal years 2018 , 2017 and 2016 , 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.
Foreign Currency	Foreign Currency The functional currency for the Company’s foreign subsidiaries is the local currency in which the respective entity is located, with the exception of F5 Networks Singapore Pte Ltd., F5 Networks (UK) Ltd., F5 Networks Benelux B.V. (Netherlands), F5 Networks Japan G.K., F5 Networks Canada Ltd., F5 Networks GmbH (Germany), F5 Networks Australia Pty, Ltd., F5 Networks (Israel) Ltd., Traffix Communication Systems Ltd. (Israel) and Versafe Ltd. (Israel), that use the U.S. dollar as their functional currency. 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 significant during the fiscal years ended September 30, 2018 , 2017 and 2016 .
Segments	Segments Management has determined that the Company was organized as, and operated in, one reportable operating segment for fiscal year 2018 and prior years: 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 accounts for stock-based compensation using the straight-line attribution method for recognizing compensation expense. The Company recognized $157.9 million , $175.3 million and $156.8 million of stock-based compensation expense for the fiscal years ended September 30, 2018 , 2017 and 2016 , respectively. As of September 30, 2018 , there was $109.6 million of total unrecognized stock-based compensation cost, the majority of which will be recognized over the next 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. The Company issues incentive awards to its employees through stock-based compensation consisting of restricted stock units (RSUs). On October 31, 2018 , the Company’s Board of Directors and Compensation Committee approved 774,313 RSUs to employees and executive officers pursuant to the Company’s annual equity awards program. The value of RSUs is determined using the fair value method, which in this case, is based on the number of shares granted and the quoted price of the Company’s common stock on the date of grant. No stock options were granted in fiscal years 2018 , 2017 and 2016 . In determining the fair value of shares issued under the Employee Stock Purchase Plan (ESPP), the Company uses the Black-Scholes option pricing model that employs the following key assumptions. Employee Stock Purchase Plan 2018 2017 2016 Risk-free interest rate 2.25 % 1.14 % 0.44 % Expected dividend — — — Expected term 0.5 years 0.5 years 0.5 years Expected volatility 18.14 % 22.03 % 29.97 % The risk-free rate is based on the U.S. Treasury yield curve in effect at the time of grant. The Company does not anticipate declaring dividends in the foreseeable future. Expected volatility is based on the annualized daily historical volatility of the Company’s stock price commensurate with the expected life of the ESPP option. Expected term of the ESPP option is based on an offering period of six months. The assumptions above 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 recognizes compensation expense for only the portion of restricted stock units 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. Fifty percent of the aggregate number of RSUs issued to executive officers vest in equal quarterly increments, and 50% are subject to the Company achieving specified performance goals. For the prior year performance stock grants, 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 performance stock grants, 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 a 15% increase in annual stand-alone software revenue compared to the prior year; and (3) 25% of the annual performance stock grant is based on relative total shareholder return 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. As of September 30, 2018 , 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, 2017 140,135 Quarterly 4 years November 1, 2021 November 1, 2016 115,347 Quarterly 4 years November 1, 2020 November 2, 2015 145,508 Quarterly 4 years November 1, 2019 November 1, 2014 171,575 Quarterly 4 years November 1, 2018 The Company recognizes compensation costs 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.
Common Stock Repurchase	Common Stock Repurchase On October 25, 2017 , 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 $3.4 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 2018, the Company repurchased and retired 4,074,170 shares at an average price of $147.29 per share and as of September 30, 2018, the Company had $573.6 million remaining authorized to purchase shares.
Earnings Per Share	Earnings 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.
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 July 2015, the FASB issued ASU 2015-11, Simplifying the Measurement of Inventory (ASU 2015-11), which changes the subsequent measurement of inventory from lower of cost or market to lower of cost and net realizable value. The Company adopted ASU 2015-11 during the first quarter of fiscal 2018. The adoption of ASU 2015-11 did not have a material impact on the Company's consolidated financial statements. In November 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes (ASU 2015-17), which requires that all deferred tax assets and liabilities be classified as noncurrent in a classified balance sheet. The Company adopted ASU 2015-17 during the first quarter of fiscal year 2018 on a retrospective basis, which resulted in reclassification of $53.0 million of deferred tax assets, net of deferred tax liabilities, from current to non-current as of September 30, 2017. In March 2016, the FASB issued ASU 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting (ASU 2016-09), which is intended to simplify several aspects of the accounting for share-based payment transactions, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification in the statement of cash flows. The Company adopted ASU 2016-09 during the first quarter of fiscal year 2018. Excess tax benefits and tax deficiencies from share-based compensation are now recorded to the consolidated income statements rather than to additional paid-in capital within equity on a prospective basis. The Company recognized $7.6 million of tax benefits for the fiscal year ended September 30, 2018. The Company also elected to prospectively apply the change in presentation requirement wherein excess tax benefits of awards are classified as operating activities in the consolidated statements of cash flows. Prior periods have not been reclassified to conform to the fiscal 2018 presentation. The Company did not elect an accounting policy change to record forfeitures as they occur and will continue to estimate forfeitures at each period. In January 2017, the FASB issued ASU 2017-04, Intangibles - Goodwill and Other: Simplifying the Test for Goodwill Impairment (ASU 2017-04), which simplifies the goodwill impairment process by eliminating Step 2 from the quantitative goodwill impairment test. Under this update, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. The new standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2019. The Company elected to early adopt ASU 2017-04 for its annual goodwill impairment test that was performed during the second quarter of fiscal 2018. The adoption of this standard did not have a material impact on the Company's consolidated financial statements. Recently Issued Accounting Pronouncements 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 will require 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 standard can be applied either retrospectively to each period presented or as a cumulative-effect adjustment as of the date of adoption. In July 2015, the FASB issued ASU 2015-14, Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date, which delays the effective date of ASU 2014-09 by one year. The updated standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017 with early adoption permitted for annual reporting periods beginning after December 15, 2016. The Company currently plans to adopt ASU 2014-09 in the first quarter of fiscal 2019 on a modified retrospective basis. The Company is finalizing system, data and process changes related to the implementation of this accounting standard. Under the new standard, the Company expects to defer and amortize incremental costs to obtain a contract, which are primarily commission costs, over the expected customer life rather than expensing them as incurred under current practice. Additionally, under the new standard, the Company would be required to recognize a portion of term license revenues upfront, at the time of delivery rather than ratably over the related contract period. The Company does not anticipate that the implementation of this updated standard and related amendments will have a material impact on its consolidated income statements. The Company is continuing to evaluate the impact that this updated standard and the related amendments will have on its consolidated balance sheets and footnote disclosures. In February 2016, the 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 of operating leases for its office and lab spaces. The guidance also requires qualitative and quantitative disclosures designed to assess the amount, timing and uncertainty of cash flows arising from leases. Adoption of the new lease standard requires measurement of leases at the beginning of the earliest period presented on a modified retrospective basis. The new standard will be effective for the Company beginning October 1, 2019. The Company anticipates that its long-term leases for office space will be recognized as lease liabilities and corresponding right-of-use assets, and will accordingly have a material impact on its consolidated balance sheets upon adoption. In July 2018, the FASB issued ASU 2018-11, Leases (Topic 842) (ASU 2018-11), which provides an optional transition method to adopt ASU 2016-02, Leases (Topic 842) by allowing lessees to apply the new standard at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. Comparative periods will still be presented under current GAAP (ASC 840), along with the applicable Topic 840 disclosures for those comparative periods. The new standard is effective at the same time as adoption of ASU 2016-02, Leases (Topic 842), which the Company is planning to adopt in the first quarter of fiscal year 2020 . The Company anticipates that its long-term leases for office space will be recognized as lease liabilities and corresponding right-of-use assets, and will accordingly have a material impact on its consolidated balance sheets upon adoption. 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 replaces the incurred loss impairment methodology in current GAAP with a methodology that reflects expected credit losses. 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 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments (ASU 2016-15), which clarifies how companies present and classify certain cash receipts and cash payments in the statement of cash flows. The new standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. Early adoption is permitted, including adoption in an interim period. The Company does not anticipate that the adoption of this standard will have a material impact on its consolidated financial statements. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash (ASU 2016-18), which will require a company’s cash flow statement to explain the changes during a reporting period of the totals for cash, cash equivalents, restricted cash, and restricted cash equivalents. Additionally, amounts for restricted cash and restricted cash equivalents are to be included with cash and cash equivalents if the cash flow statement includes a reconciliation of the total cash balances for a reporting period. The new standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. 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 January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business (ASU 2017-01), which provides a more robust framework to use in determining when a set of assets and activities is considered a business. The new standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. Early adoption is permitted for certain transactions. The Company will evaluate the impact of adopting this standard prospectively, for any transaction involving the acquisition or disposal of assets or businesses. In May 2017, the FASB issued ASU 2017-09, Compensation-Stock Compensation (ASU 2017-09), which provides clarification on when modification accounting should be used for changes to the terms or conditions of a share-based payment award. This ASU does not change the accounting for modifications but clarifies that modification accounting guidance should only be applied if there is a change to the value, vesting conditions or award classification and would not be required if the changes are considered non-substantive. The new standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. 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 is currently assessing the impact that this updated standard will have on its consolidated financial statements and footnote disclosures.

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Tables)	12 Months Ended
	Sep. 30, 2018
Accounting Policies [Abstract]
Schedule Of Inventories	Inventories consist of the following (in thousands): September 30, 2018 2017 Finished goods $ 21,339 $ 20,280 Raw materials 9,229 9,554 $ 30,568 $ 29,834
Schedule Of Property And Equipment	Property and equipment consist of the following (in thousands): September 30, 2018 2017 Computer equipment $ 194,847 $ 177,235 Office furniture and equipment 31,625 32,781 Leasehold improvements 107,615 88,410 334,087 298,426 Accumulated depreciation and amortization (189,045 ) (176,006 ) $ 145,042 $ 122,420
Schedule Of Assumptions In Determining The Fair Value Of Shares Issued Under The Employee Stock Purchase Plan	Employee Stock Purchase Plan 2018 2017 2016 Risk-free interest rate 2.25 % 1.14 % 0.44 % Expected dividend — — — Expected term 0.5 years 0.5 years 0.5 years Expected volatility 18.14 % 22.03 % 29.97 %
Schedule of Nonvested Restricted Stock Units Activity	As of September 30, 2018 , 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, 2017 140,135 Quarterly 4 years November 1, 2021 November 1, 2016 115,347 Quarterly 4 years November 1, 2020 November 2, 2015 145,508 Quarterly 4 years November 1, 2019 November 1, 2014 171,575 Quarterly 4 years November 1, 2018
Schedule Of Computation Of Basic And Diluted Net Income Per Share	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, 2018 2017 2016 Numerator Net income $ 453,689 $ 420,761 $ 365,855 Denominator Weighted average shares outstanding — basic 61,262 64,173 67,433 Dilutive effect of common shares from stock options and restricted stock units 751 602 551 Weighted average shares outstanding — diluted 62,013 64,775 67,984 Basic net income per share $ 7.41 $ 6.56 $ 5.43 Diluted net income per share $ 7.32 $ 6.50 $ 5.38

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Sep. 30, 2018
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, 2018 , were as follows (in thousands): Fair Value Measurements at Reporting Date Using Fair Value at September 30, 2018 Quoted Prices in Active Markets for Identical Securities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash equivalents $ 41,468 $ 13,118 $ — $ 54,586 Short-term investments Available-for-sale securities — certificates of deposit — 2,970 — 2,970 Available-for-sale securities — corporate bonds and notes — 393,750 — 393,750 Available-for-sale securities — municipal bonds and notes — 22,524 — 22,524 Available-for-sale securities — U.S. government securities — 120,078 — 120,078 Available-for-sale securities — U.S. government agency securities — 75,383 — 75,383 Long-term investments Available-for-sale securities — corporate bonds and notes — 367,710 — 367,710 Available-for-sale securities — municipal bonds and notes — 24,286 — 24,286 Available-for-sale securities — U.S. government securities — 12,771 — 12,771 Available-for-sale securities — U.S. government agency securities — 6,417 — 6,417 Total $ 41,468 $ 1,039,007 $ — $ 1,080,475 The Company’s financial assets measured at fair value on a recurring basis subject to the disclosure requirements at September 30, 2017 , were as follows (in thousands): Fair Value Measurements at Reporting Date Using Fair Value at September 30, 2017 Quoted Prices in Active Markets for Identical Securities (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Cash equivalents $ 13,967 $ 3,192 $ — $ 17,159 Short-term investments Available-for-sale securities — corporate bonds and notes — 172,493 — 172,493 Available-for-sale securities — municipal bonds and notes — 67,409 — 67,409 Available-for-sale securities — U.S. government securities — 72,930 — 72,930 Available-for-sale securities — U.S. government agency securities — 30,868 — 30,868 Long-term investments Available-for-sale securities — corporate bonds and notes — 191,782 — 191,782 Available-for-sale securities — municipal bonds and notes — 26,643 — 26,643 Available-for-sale securities — U.S. government securities — 29,374 — 29,374 Available-for-sale securities — U.S. government agency securities — 37,003 — 37,003 Total $ 13,967 $ 631,694 $ — $ 645,661

Short-Term And Long-Term Inve_2

Short-Term And Long-Term Investments (Tables)	12 Months Ended
	Sep. 30, 2018
Schedule of Investments [Line Items]
Schedule Of Short-Term And Long-Term Investments	Short-term investments consist of the following (in thousands): September 30, 2018 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Certificates of deposit $ 2,970 $ — $ — $ 2,970 Corporate bonds and notes 394,684 9 (943 ) 393,750 Municipal bonds and notes 22,588 1 (65 ) 22,524 U.S. government securities 120,283 — (205 ) 120,078 U.S. government agency securities 75,587 — (204 ) 75,383 $ 616,112 $ 10 $ (1,417 ) $ 614,705 September 30, 2017 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate bonds and notes $ 172,560 $ 25 $ (92 ) $ 172,493 Municipal bonds and notes 67,382 36 (9 ) 67,409 U.S. government securities 72,991 — (61 ) 72,930 U.S. government agency securities 30,954 — (86 ) 30,868 $ 343,887 $ 61 $ (248 ) $ 343,700 Long-term investments consist of the following (in thousands): September 30, 2018 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate bonds and notes $ 370,377 $ 25 $ (2,692 ) $ 367,710 Municipal bonds and notes 24,468 — (182 ) 24,286 U.S. government securities 12,956 — (185 ) 12,771 U.S. government agency securities 6,500 — (83 ) 6,417 $ 414,301 $ 25 $ (3,142 ) $ 411,184 September 30, 2017 Cost or Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate bonds and notes $ 192,278 $ 25 $ (521 ) $ 191,782 Municipal bonds and notes 26,639 46 (42 ) 26,643 U.S. government securities 29,427 — (53 ) 29,374 U.S. government agency securities 37,164 — (161 ) 37,003 $ 285,508 $ 71 $ (777 ) $ 284,802
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, 2018 (in thousands): Less Than 12 Months 12 Months or Greater Total September 30, 2018 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Corporate bonds and notes $ 543,729 $ (1,800 ) $ 152,097 $ (1,835 ) $ 695,826 $ (3,635 ) Municipal bonds and notes 26,846 (123 ) 14,363 (124 ) 41,209 (247 ) U.S. government securities 103,470 (281 ) 29,379 (109 ) 132,849 (390 ) U.S. government agency securities 44,812 (110 ) 36,987 (177 ) 81,799 (287 ) Total $ 718,857 $ (2,314 ) $ 232,826 $ (2,245 ) $ 951,683 $ (4,559 ) 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, 2017 (in thousands): Less Than 12 Months 12 Months or Greater Total September 30, 2017 Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Fair Value Gross Unrealized Losses Corporate bonds and notes $ 262,852 $ (528 ) $ 35,401 $ (85 ) $ 298,253 $ (613 ) Municipal bonds and notes 30,256 (49 ) 881 (2 ) 31,137 (51 ) U.S. government securities 94,312 (105 ) 7,992 (9 ) 102,304 (114 ) U.S. government agency securities 36,121 (83 ) 31,750 (164 ) 67,871 (247 ) Total $ 423,541 $ (765 ) $ 76,024 $ (260 ) $ 499,565 $ (1,025 )

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	12 Months Ended
	Sep. 30, 2018
Balance Sheet Details [Abstract]
Schedule Of Other Assets	Other assets consist of the following (in thousands): September 30, 2018 2017 Acquired and developed technology and software development costs $ 17,641 $ 25,085 Intangible assets 13,618 17,469 Restricted cash and deposits 10,927 11,221 $ 42,186 $ 53,775
Schedule Of Intangible Assets	Intangible assets are included in other assets on the balance sheet and consist of the following (in thousands): 2018 2017 Gross Carrying Amount Accumulated Amortization Net Carrying Amount Gross Carrying Amount Accumulated Amortization Net Carrying Amount Acquired and developed technology and software development costs $ 63,672 $ (46,031 ) $ 17,641 $ 69,307 $ (44,222 ) $ 25,085 Customer relationships 8,242 (4,376 ) 3,866 8,242 (3,552 ) 4,690 Patents and trademarks 18,971 (9,219 ) 9,752 19,756 (7,159 ) 12,597 Trade names 973 (973 ) — 973 (791 ) 182 Non-compete covenants 1,960 (1,960 ) — 2,532 (2,532 ) — $ 93,818 $ (62,559 ) $ 31,259 $ 100,810 $ (58,256 ) $ 42,554
Schedule Of Estimated Amortization Expense For Intangible Assets	Estimated amortization expense for intangible assets for the five succeeding fiscal years is as follows (in thousands): 2019 $ 6,858 2020 6,363 2021 6,232 2022 5,026 2023 4,229 $ 28,708
Schedule Of Accrued Liabilities	Accrued liabilities consist of the following (in thousands): September 30, 2018 2017 Payroll and benefits $ 104,815 $ 109,088 Sales and marketing 2,743 6,654 Restructuring 8,268 7,741 Income tax accruals 17,795 15,519 Other tax accruals 9,861 13,429 Other 37,497 34,948 $ 180,979 $ 187,379

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2018
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, 2018 2017 2016 United States $ 441,336 $ 452,869 $ 465,738 International 162,424 122,648 84,153 $ 603,760 $ 575,517 $ 549,891
Schedule Of Provision For Income Taxes (Benefit)	The provision for income taxes (benefit) consists of the following (in thousands): Years Ended September 30, 2018 2017 2016 Current U.S. federal $ 78,454 $ 113,105 $ 129,728 State 9,800 10,381 16,821 Foreign 41,040 34,679 31,015 Total 129,294 158,165 177,564 Deferred U.S. federal 21,259 964 9,770 State 725 99 (1,029 ) Foreign (1,207 ) (4,472 ) (2,269 ) Total 20,777 (3,409 ) 6,472 $ 150,071 $ 154,756 $ 184,036
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, 2018 2017 2016 Income tax provision at statutory rate $ 147,921 $ 201,431 $ 192,462 State taxes, net of federal benefit 9,349 9,235 13,434 Foreign operations (6,696 ) (40,606 ) (9,199 ) Research and development and other credits (13,159 ) (12,795 ) (18,368 ) Domestic manufacturing deduction (9,722 ) (15,802 ) (14,624 ) Stock-based and other compensation (150 ) 12,688 17,137 Impacts of the Tax Cuts and Jobs Act 21,015 — — Other 1,513 605 3,194 $ 150,071 $ 154,756 $ 184,036
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, 2018 2017 Deferred tax assets Net operating loss carry-forwards $ 11,540 $ 11,235 Allowance for doubtful accounts 368 1,236 Accrued compensation and benefits 8,202 11,617 Inventories and related reserves 324 715 Stock-based compensation 5,570 11,857 Deferred revenue 29,290 43,371 Other accruals and reserves 14,409 17,924 Tax credit carryforwards 12,177 7,873 Depreciation 671 628 82,551 106,456 Valuation allowance (22,780 ) (18,189 ) 59,771 88,267 Deferred tax liabilities Purchased intangibles and other (10,678 ) (17,459 ) Depreciation (12,277 ) (16,893 ) Other accruals and reserves (3,410 ) (676 ) (26,365 ) (35,028 ) Net deferred tax assets $ 33,406 $ 53,239
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 2018 , 2017 and 2016 (in thousands): 2018 2017 2016 Balance, beginning of period $ 23,135 $ 13,687 $ 9,562 Gross increases related to prior period tax positions 2,715 2,769 1,622 Gross decreases related to prior period tax positions — — (7 ) Gross increases related to current period tax positions 8,230 8,507 4,441 Decreases relating to settlements with tax authorities — (240 ) (521 ) Reductions due to lapses of statute of limitations (2,408 ) (1,588 ) (1,410 ) Balance, end of period $ 31,672 $ 23,135 $ 13,687

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Sep. 30, 2018
Share-based Compensation [Abstract]
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 Performance Stock Units Weighted Average Grant Date Fair Value Outstanding Restricted Stock Units Weighted Average Grant Date Fair Value Balance, September 30, 2017 13,871 $ 121.44 1,347,431 $ 127.89 Units granted 62,396 118.97 1,307,589 127.24 Units vested (24,374 ) 145.23 (1,191,577 ) 150.75 Units cancelled (27,814 ) 119.15 (312,573 ) 125.46 Balance, September 30, 2018 24,079 $ 119.01 1,150,870 $ 129.35
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 Shares Weighted Average Exercise Price per Share Balance, September 30, 2017 976 $ 3.18 Options granted — — Options exercised (814 ) 3.07 Options cancelled — — Balance, September 30, 2018 162 $ 3.76
Schedule Of Outstanding Stock Options Currently Exercisable, Vested And Expected To Vest	Number of Shares Weighted Average Remaining Contractual Life (in Years) Weighted Average Exercise Price per Share Aggregate Intrinsic Value(1) (In thousands) Stock options outstanding 162 4.73 $ 3.76 $ 32 Exercisable 162 4.73 $ 3.76 $ 32 Vested and expected to vest 162 4.73 $ 3.76 $ 32 (1) Aggregate intrinsic value represents the difference between the fair value of the Company’s common stock underlying these options at September 30, 2018 and the related exercise prices.
Schedule Of Equity Based Awards (Including Stock Options And Restricted Stock Units)	As of September 30, 2018 , equity based awards (including stock options and restricted stock units) are available for future issuance as follows: Awards Available for Grant Balance, September 30, 2017 3,081,285 Granted (1,369,985 ) Cancelled 341,000 Additional shares reserved (terminated), net (613 ) Balance, September 30, 2018 2,051,687

Commitment And Contingencies (T

Commitment And Contingencies (Tables)	12 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Schedule Of Future Minimum Operating Lease Payments, Net Of Sublease Income	Future minimum operating lease payments, net of sublease income, are as follows (in thousands): Gross Lease Payments Sublease Income Net Lease Payments 2019 30,870 — 30,870 2020 45,418 — 45,418 2021 42,615 — 42,615 2022 40,285 — 40,285 2023 31,238 — 31,238 Thereafter 271,882 — 271,882 $ 462,308 $ — $ 462,308

Restructuring Charges (Tables)

Restructuring Charges (Tables)	12 Months Ended
	Sep. 30, 2018
Restructuring and Related Activities [Abstract]
Schedule of restructuring charges	During the year ended September 30, 2018, the following activity was recorded (in thousands): Employee Severance, Benefits and Related Costs Accrued expenses, October 1, 2017 $ 7,741 Restructuring charges 18,426 Cash payments (17,899 ) Non-cash items — Accrued expenses, September 30, 2018 $ 8,268

Geographic Sales And Signific_2

Geographic Sales And Significant Customers (Tables)	12 Months Ended
	Sep. 30, 2018
Segments, Geographical Areas [Abstract]
Schedule Of Revenues By Geographic Region	The following presents revenues by geographic region (in thousands): Years Ended September 30, 2018 2017 2016 Americas: United States $ 1,088,270 $ 1,075,222 $ 1,019,054 Other 116,073 110,298 106,228 Total Americas 1,204,343 1,185,520 1,125,282 EMEA 546,239 506,571 487,966 Japan 95,251 95,055 94,767 Asia Pacific 315,574 302,895 287,019 $ 2,161,407 $ 2,090,041 $ 1,995,034
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, 2018 2017 2016 Ingram Micro, Inc. 16.6 % 16.1 % 14.9 % Tech Data 1 11.6 % 12.4 % 13.3 % Synnex Corporation 2 10.8 % — — Arrow ECS 10.7 % 10.4 % 10.1 % Westcon Group, Inc. 2 10.4 % 17.7 % 18.7 % (1) On February 27, 2017, Tech Data completed the acquisition of Avnet Technology Solutions. Revenues for the year ended September 30, 2017 represent combined revenues for Tech Data and Avnet while revenues for years ended September 30, 2016 and 2015 represent revenues from Avnet only. (2) On September 1, 2017, Synnex Corporation completed the acquisition of Westcon Americas.
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, 2018 2017 United States $ 126,790 $ 103,486 EMEA 12,538 15,054 Other countries 5,714 3,880 $ 145,042 $ 122,420

Quarterly Results Of Operatio_2

Quarterly Results Of Operations (Unaudited) (Tables)	12 Months Ended
	Sep. 30, 2018
Quarterly Financial Data [Abstract]
Schedule Of Quarterly Results Of Operations	Three Months Ended Sept. 30, 2018 June 30, 2018 March 31, 2018 Dec. 31, 2017 Sept. 30, 2017 June 30, 2017 March 31, 2017 Dec. 31, 2016 (unaudited and in thousands, except per share data) Net revenues Products $ 256,412 $ 238,835 $ 237,558 $ 227,303 $ 248,990 $ 235,109 $ 241,080 $ 239,483 Services 306,297 303,368 295,746 295,888 289,008 282,728 277,168 276,475 Total 562,709 542,203 533,304 523,191 537,998 517,837 518,248 515,958 Cost of net revenues Products 48,505 45,164 44,127 43,265 46,641 43,787 43,928 41,676 Services 44,935 45,845 45,518 44,122 43,900 45,983 43,984 43,586 Total 93,440 91,009 89,645 87,387 90,541 89,770 87,912 85,262 Gross profit 469,269 451,194 443,659 435,804 447,457 428,067 430,336 430,696 Operating expenses Sales and marketing 160,425 165,806 169,970 167,934 162,068 160,952 164,705 164,514 Research and development 95,078 94,061 91,056 85,889 85,479 88,602 89,234 87,050 General and administrative 41,748 39,374 39,276 39,984 37,832 39,368 38,009 41,678 Litigation expense — — — — 525 1 (135 ) — Restructuring charges 18,426 — — — 12,718 — — — Total operating expenses 315,677 299,241 300,302 293,807 298,622 288,923 291,813 293,242 Income from operations 153,592 151,953 143,357 141,997 148,835 139,144 138,523 137,454 Other income, net 5,667 2,259 2,790 2,145 5,027 2,589 1,302 2,643 Income before income taxes 159,259 154,212 146,147 144,142 153,862 141,733 139,825 140,097 Provision for income taxes 26,378 31,469 36,511 55,713 18,119 44,071 46,687 45,879 Net income $ 132,881 $ 122,743 $ 109,636 $ 88,429 $ 135,743 $ 97,662 $ 93,138 $ 94,218 Net income per share — basic $ 2.20 $ 2.01 $ 1.79 $ 1.42 $ 2.15 $ 1.53 $ 1.44 $ 1.45 Weighted average shares — basic 60,462 60,970 61,420 62,195 63,088 63,935 64,479 65,195 Net income per share — diluted $ 2.18 $ 1.99 $ 1.77 $ 1.41 $ 2.14 $ 1.52 $ 1.43 $ 1.44 Weighted average shares — diluted 61,070 61,633 62,059 62,550 63,446 64,361 65,028 65,645

Summary Of Significant Accoun_4

Summary Of Significant Accounting Policies (Narrative) (Details)	Oct. 31, 2018USD ($)shares	Sep. 30, 2018USD ($)segment$ / sharesshares	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)	Oct. 25, 2017USD ($)	Apr. 20, 2016USD ($)
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Number of Reportable Segments | segment		1
Other Assets
Amortization expense related to acquired technology		$ 11,100,000	$ 12,300,000	$ 13,900,000
Revenue Recognition
VSOE Percentage Which Constitutes Substantial Majority of Transactions Priced Within a Narrow Range		80.00%
Range of VSOE to median sales price		15.00%
Advertising
Advertising costs		$ 4,600,000	3,500,000	4,000,000
Common Stock Repurchase
Shares repurchased and retired | shares		4,074,170
Shares repurchased and retired, average price per share | $ / shares		$ 147.29
Stock repurchase program, remaining amount		$ 573,600,000
Excess tax benefit (deficiency) from share-based compensation recorded to the consolidated income statements due to adoption of ASU 2016-09		$ 7,600,000
Minimum [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Award vesting period		1 year
Revenue Recognition
Domestic accounts receivable terms of payment		30 days
International accounts receivable terms of payment		30 days
Common Stock Repurchase
Useful life (in years)		3 years
Maximum [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Award vesting period		4 years
Revenue Recognition
Domestic accounts receivable terms of payment		45 days
International accounts receivable terms of payment		120 days
Common Stock Repurchase
Useful life (in years)		10 years
Software and Software Development Costs [Member] | Minimum [Member]
Common Stock Repurchase
Useful life (in years)		3 years
Software and Software Development Costs [Member] | Maximum [Member]
Common Stock Repurchase
Useful life (in years)		5 years
Hardware [Member]
Guarantees and Product Warranties
Standard product warranty period		1 year
Developed Technology Rights [Member]
Other Assets
Amortization expense related to acquired technology		$ 7,400,000	$ 8,800,000	$ 10,600,000
Subsequent Event [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Equity instruments other than options, grants in period | shares	774,313
Restricted Stock Units (RSUs) [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Award vesting period		2 years	2 years	2 years
Restricted Stock Units (RSUs) [Member] | Annual Equity Program [Member]
Common Stock Repurchase
Percentage of the aggregate number of Rsus granted that vest in equal quarterly increments		50.00%
Portion of RSU grant subject to Company achieving specified quarterly revenue and EBITDA goals		50.00%
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%
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%
November 1, 2016 [Member] | Restricted Stock Units (RSUs) [Member] | Annual Equity Program [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Equity instruments other than options, grants in period | shares		115,347
Award vesting period		4 years
November 2, 2015 [Member] | Restricted Stock Units (RSUs) [Member] | Annual Equity Program [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Equity instruments other than options, grants in period | shares		145,508
Award vesting period		4 years
November 1, 2014 [Member] | Restricted Stock Units (RSUs) [Member] | Annual Equity Program [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Equity instruments other than options, grants in period | shares		171,575
Award vesting period		4 years
October 26, 2010 Program [Member]
Common Stock Repurchase
Common stock share repurchase program, amount authorized					$ 1,000,000,000	$ 3,400,000,000
October 26, 2010 Program [Member] | Subsequent Event [Member]
Common Stock Repurchase
Common stock share repurchase program, amount authorized	$ 1,000,000,000
Geographic Concentration Risk [Member] | Customer Five [Member] | Accounts Receivable [Member]
Concentration of Credit Risk
Concentration risk percentage		10.30%	13.60%
Geographic Concentration Risk [Member] | Customer Two [Member] | Accounts Receivable [Member]
Concentration of Credit Risk
Concentration risk percentage		16.60%
Geographic Concentration Risk [Member] | Customer Four [Member] | Accounts Receivable [Member]
Concentration of Credit Risk
Concentration risk percentage			11.50%
Accounting Standards Update 2015-17 [Member]
Schedule Of Summary Of Significant Accounting Policies [Line Items]
Deferred Tax Assets, Net, Current			$ (53,000,000)

Summary Of Significant Accoun_5

Summary Of Significant Accounting Policies (Schedule Of Inventories) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Accounting Policies [Abstract]
Finished goods	$ 21,339	$ 20,280
Raw materials	9,229	9,554
Inventories, Total	$ 30,568	$ 29,834

Summary Of Significant Accoun_6

Summary Of Significant Accounting Policies (Property And Equipment) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Property, Plant and Equipment [Line Items]
Computer equipment	$ 194,847	$ 177,235
Office furniture and equipment	31,625	32,781
Leasehold improvements	107,615	88,410
Property and equipment, gross	334,087	298,426
Accumulated depreciation and amortization	(189,045)	(176,006)
Property and equipment, net	145,042	122,420
Depreciation and amortization expense	$ 45,900	$ 44,600	$ 36,400
Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	5 years

Summary Of Significant Accoun_7

Summary Of Significant Accounting Policies (Stock-Based Compensation) (Details) - USD ($) $ in Millions	Oct. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Allocated Share-based Compensation Expense		$ 157.9	$ 175.3	$ 156.8
Unrecognized stock-based compensation cost		$ 109.6
Unrecognized stock-based compensation cost, period for recognition, years		2 years
Fair Value Assumptions
Risk-free interest rate		2.25%	1.14%	0.44%
Expected dividend		0.00%	0.00%	0.00%
Expected term		6 months	6 months	6 months
Expected volatility		18.14%	22.03%	29.97%
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
Subsequent Event [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instruments other than options, grants in period	774,313
Annual Equity Program [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage Of Annual Performance Stock Grant Based On Achieving Annual Revenue Goal		50.00%
Percentage of the aggregate number of Rsus granted that vest in equal quarterly increments		50.00%
Percentage of quarterly performance stock grant based on achieving quarterly revenue goal		70.00%
Grant based on achieving EBITDA goal		30.00%
Percentage of over-achievement threshold to which the goals are entitled		100.00%
Percentage of quarterly revenue 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%
Fair Value Assumptions
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		15.00%
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%
Annual Equity Program [Member] | November 1, 2017 [Member] | Restricted Stock Units (RSUs) [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 2, 2015 [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instruments other than options, grants in period		145,508
Award vesting period		4 years
Annual Equity Program [Member] | November 1, 2014 [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instruments other than options, grants in period		171,575
Award vesting period		4 years

Summary Of Significant Accoun_8

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, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Accounting Policies [Abstract]
Net income	$ 132,881	$ 122,743	$ 109,636	$ 88,429	$ 135,743	$ 97,662	$ 93,138	$ 94,218	$ 453,689	$ 420,761	$ 365,855
Weighted average shares outstanding - basic	60,462	60,970	61,420	62,195	63,088	63,935	64,479	65,195	61,262	64,173	67,433
Dilutive effect of common shares from stock options and restricted stock units									751	602	551
Weighted average shares outstanding - diluted	61,070	61,633	62,059	62,550	63,446	64,361	65,028	65,645	62,013	64,775	67,984
Basic net income per share (USD per share)	$ 2.20	$ 2.01	$ 1.79	$ 1.42	$ 2.15	$ 1.53	$ 1.44	$ 1.45	$ 7.41	$ 6.56	$ 5.43
Diluted net income per share (USD per share)	$ 2.18	$ 1.99	$ 1.77	$ 1.41	$ 2.14	$ 1.52	$ 1.43	$ 1.44	$ 7.32	$ 6.50	$ 5.38

Fair Value Measurements (Schedu

Fair Value Measurements (Schedule Of Financial Assets Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Cash equivalents, fair value	$ 54,586	$ 17,159
Financial assets measured at fair value on a recurring basis, total	1,080,475	645,661
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	41,468	13,967
Financial assets measured at fair value on a recurring basis, total	41,468	13,967
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	13,118	3,192
Financial assets measured at fair value on a recurring basis, total	1,039,007	631,694
Short-Term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	614,705	343,700
Short-Term Investments [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	2,970
Short-Term Investments [Member] | 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	2,970
Short-Term Investments [Member] | Corporate Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	393,750	172,493
Short-Term Investments [Member] | 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	393,750	172,493
Short-Term Investments [Member] | Municipal Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	22,524	67,409
Short-Term Investments [Member] | 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	22,524	67,409
Short-Term Investments [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	120,078	72,930
Short-Term Investments [Member] | 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	120,078	72,930
Short-Term Investments [Member] | U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	75,383	30,868
Short-Term Investments [Member] | U.S. Government Agency 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	75,383	30,868
Long-Term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	411,184	284,802
Long-Term Investments [Member] | Corporate Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	367,710	191,782
Long-Term Investments [Member] | 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	367,710	191,782
Long-Term Investments [Member] | Municipal Bonds And Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	24,286	26,643
Long-Term Investments [Member] | 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	24,286	26,643
Long-Term Investments [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	12,771	29,374
Long-Term Investments [Member] | 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	12,771	29,374
Long-Term Investments [Member] | U.S. Government Agency Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]
Available-for-sale securities	6,417	37,003
Long-Term Investments [Member] | U.S. Government Agency 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	$ 6,417	$ 37,003

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, 2018	Sep. 30, 2017
Long-Term Investments [Member]
Investment [Line Items]
Cost or Amortized Cost	$ 414,301	$ 285,508
Gross Unrealized Gains	25	71
Gross Unrealized Losses	(3,142)	(777)
Fair Value	411,184	284,802
Long-Term Investments [Member] | US Government Agencies Debt Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	6,500	37,164
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(83)	(161)
Fair Value	6,417	37,003
Long-Term Investments [Member] | Corporate Debt Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	370,377	192,278
Gross Unrealized Gains	25	25
Gross Unrealized Losses	(2,692)	(521)
Fair Value	367,710	191,782
Long-Term Investments [Member] | Municipal Bonds And Notes [Member]
Investment [Line Items]
Cost or Amortized Cost	24,468	26,639
Gross Unrealized Gains	0	46
Gross Unrealized Losses	(182)	(42)
Fair Value	24,286	26,643
Long-Term Investments [Member] | US Government Debt Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	12,956	29,427
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(185)	(53)
Fair Value	12,771	29,374
Short-Term Investments [Member]
Investment [Line Items]
Cost or Amortized Cost	616,112	343,887
Gross Unrealized Gains	10	61
Gross Unrealized Losses	(1,417)	(248)
Fair Value	614,705	343,700
Short-Term Investments [Member] | Certificates of Deposit [Member]
Investment [Line Items]
Cost or Amortized Cost	2,970
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	2,970
Short-Term Investments [Member] | US Government Agencies Debt Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	75,587	30,954
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(204)	(86)
Fair Value	75,383	30,868
Short-Term Investments [Member] | Corporate Debt Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	394,684	172,560
Gross Unrealized Gains	9	25
Gross Unrealized Losses	(943)	(92)
Fair Value	393,750	172,493
Short-Term Investments [Member] | Municipal Bonds And Notes [Member]
Investment [Line Items]
Cost or Amortized Cost	22,588	67,382
Gross Unrealized Gains	1	36
Gross Unrealized Losses	(65)	(9)
Fair Value	22,524	67,409
Short-Term Investments [Member] | US Government Debt Securities [Member]
Investment [Line Items]
Cost or Amortized Cost	120,283	72,991
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(205)	(61)
Fair Value	$ 120,078	$ 72,930

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, 2018	Sep. 30, 2017
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months	$ 718,857	$ 423,541
Available-For-Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses Accumulated In Investments	(2,314)	(765)
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater	232,826	76,024
Available-For-Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Aggregate Losses Accumulated In Investments	(2,245)	(260)
Fair Value, Continuous Loss Position, Unrealized Loss, Total	951,683	499,565
Available-For-Sale Securities, Continuous Unrealized Loss Position, Aggregate Losses Accumulated In Investments	(4,559)	(1,025)
Corporate Bonds And Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months	543,729	262,852
Available-For-Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses Accumulated In Investments	(1,800)	(528)
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater	152,097	35,401
Available-For-Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Aggregate Losses Accumulated In Investments	(1,835)	(85)
Fair Value, Continuous Loss Position, Unrealized Loss, Total	695,826	298,253
Available-For-Sale Securities, Continuous Unrealized Loss Position, Aggregate Losses Accumulated In Investments	(3,635)	(613)
Municipal Bonds And Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months	26,846	30,256
Available-For-Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses Accumulated In Investments	(123)	(49)
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater	14,363	881
Available-For-Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Aggregate Losses Accumulated In Investments	(124)	(2)
Fair Value, Continuous Loss Position, Unrealized Loss, Total	41,209	31,137
Available-For-Sale Securities, Continuous Unrealized Loss Position, Aggregate Losses Accumulated In Investments	(247)	(51)
US Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months	103,470	94,312
Available-For-Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses Accumulated In Investments	(281)	(105)
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater	29,379	7,992
Available-For-Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Aggregate Losses Accumulated In Investments	(109)	(9)
Fair Value, Continuous Loss Position, Unrealized Loss, Total	132,849	102,304
Available-For-Sale Securities, Continuous Unrealized Loss Position, Aggregate Losses Accumulated In Investments	(390)	(114)
U.S. Government Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months	44,812	36,121
Available-For-Sale Securities, Continuous Unrealized Loss Position, Less Than 12 Months, Aggregate Losses Accumulated In Investments	(110)	(83)
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater	36,987	31,750
Available-For-Sale Securities, Continuous Unrealized Loss Position, 12 Months Or Longer, Aggregate Losses Accumulated In Investments	(177)	(164)
Fair Value, Continuous Loss Position, Unrealized Loss, Total	81,799	67,871
Available-For-Sale Securities, Continuous Unrealized Loss Position, Aggregate Losses Accumulated In Investments	$ (287)	$ (247)

Balance Sheet Details (Schedule

Balance Sheet Details (Schedule Of Other Assets) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Balance Sheet Details [Abstract]
Acquired and developed technology and software development costs	$ 17,641	$ 25,085
Intangible assets	13,618	17,469
Restricted cash and deposits	10,927	11,221
Other assets	42,186	53,775
Amortization expense related to other assets	$ 11,100	$ 12,300	$ 13,900

Balance Sheet Details (Schedu_2

Balance Sheet Details (Schedule Of Intangible Assets) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 93,818	$ 100,810
Accumulated Amortization	(62,559)	(58,256)
Net Carrying Amount	31,259	42,554
Developed Technology Rights [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	63,672	69,307
Accumulated Amortization	(46,031)	(44,222)
Net Carrying Amount	17,641	25,085
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	8,242	8,242
Accumulated Amortization	(4,376)	(3,552)
Net Carrying Amount	3,866	4,690
Patents And Trademarks [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	18,971	19,756
Accumulated Amortization	(9,219)	(7,159)
Net Carrying Amount	9,752	12,597
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	973	973
Accumulated Amortization	(973)	(791)
Net Carrying Amount	0	182
Non-Compete Covenants [Member]
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	1,960	2,532
Accumulated Amortization	(1,960)	(2,532)
Net Carrying Amount	$ 0	$ 0

Balance Sheet Details (Schedu_3

Balance Sheet Details (Schedule Of Estimated Amortization Expense For Intangible Assets) (Details) $ in Thousands	Sep. 30, 2018USD ($)
Balance Sheet Details [Abstract]
2,019	$ 6,858
2,020	6,363
2,021	6,232
2,022	5,026
2,023	4,229
Total estimated amortization expense	$ 28,708

Balance Sheet Details (Schedu_4

Balance Sheet Details (Schedule Of Accrued Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Balance Sheet Details [Abstract]
Payroll and benefits	$ 104,815	$ 109,088
Sales and marketing	2,743	6,654
Restructuring	8,268	7,741
Income tax accruals	17,795	15,519
Other tax accruals	9,861	13,429
Other	37,497	34,948
Total accrued liabilities	$ 180,979	$ 187,379

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Operating Loss Carryforwards [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		24.50%
Tax Cuts and Jobs Act Of 2017, Incomplete Accounting, Transition Tax For Accumulated Foreign Earnings, Provisional Income Tax Expense (Benefit)	$ 7,000	$ 7,000
Tax Cuts and Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Deferred Tax Asset, Provisional Income Tax Expense (Benefit)		14,000
Effective Income Tax Rate Reconciliation, Tax Credit, Foreign, Amount			$ 21,000
Income Tax Holiday, Aggregate Dollar Amount		$ 6,400	$ 6,900
Income Tax Holiday, Income Tax Benefits Per Share		$ 0.10	$ 0.11
Deferred Tax Assets, Tax Credit Carryforwards		$ 12,177	$ 7,873
Valuation Allowance, Deferred Tax Asset, Change in Amount		4,600	3,900
Unrecognized Tax Benefits		31,672	23,135	$ 13,687	$ 9,562
Unrecognized Tax Benefits that Would Impact Effective Tax Rate		23,100	18,300	11,100
Interest expense related to uncertain tax positions		437	258	$ 18
Unrecognized tax benefits, interest expenses accrued		1,615	$ 1,178
Foreign [Member]
Operating Loss Carryforwards [Line Items]
Operating loss carry-forwards, net		58,400
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration		4,100
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards		8,200
Deferred Tax Assets, Tax Credit Carryforwards, Subject to Expiration		$ 3,600

Income Taxes (Components Of Inc

Income Taxes (Components Of Income Before Income Taxes) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
United States									$ 441,336	$ 452,869	$ 465,738
International									162,424	122,648	84,153
Income before income taxes	$ 159,259	$ 154,212	$ 146,147	$ 144,142	$ 153,862	$ 141,733	$ 139,825	$ 140,097	$ 603,760	$ 575,517	$ 549,891

Income Taxes (Schedule Of Provi

Income Taxes (Schedule Of Provision For Income Taxes (Benefit)) (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Current, U.S. federal									$ 78,454	$ 113,105	$ 129,728
Current, State									9,800	10,381	16,821
Current, Foreign									41,040	34,679	31,015
Total									129,294	158,165	177,564
Deferred, U.S. federal									21,259	964	9,770
Deferred, State									725	99	(1,029)
Deferred, Foreign									(1,207)	(4,472)	(2,269)
Total									20,777	(3,409)	6,472
Income taxes (benefit)	$ 26,378	$ 31,469	$ 36,511	$ 55,713	$ 18,119	$ 44,071	$ 46,687	$ 45,879	$ 150,071	$ 154,756	$ 184,036

Income Taxes (Schedule Of Effec

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, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
Income tax provision at statutory rate									$ 147,921	$ 201,431	$ 192,462
State taxes, net of federal benefit									9,349	9,235	13,434
Foreign operations									(6,696)	(40,606)	(9,199)
Research and development and other credits									(13,159)	(12,795)	(18,368)
Domestic manufacturing deduction									(9,722)	(15,802)	(14,624)
Stock-based and other compensation									(150)	12,688	17,137
EffectiveIncomeTaxRateReconciliationTaxCutsAndJobsActAmount									21,015	0	0
Other									1,513	605	3,194
Income taxes (benefit)	$ 26,378	$ 31,469	$ 36,511	$ 55,713	$ 18,119	$ 44,071	$ 46,687	$ 45,879	$ 150,071	$ 154,756	$ 184,036

Income Taxes (Schedule Of Tax E

Income Taxes (Schedule Of Tax Effects To Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Net operating loss carry-forwards	$ 11,540	$ 11,235
Allowance for doubtful accounts	368	1,236
Accrued compensation and benefits	8,202	11,617
Inventories and related reserves	324	715
Stock-based compensation	5,570	11,857
Deferred revenue	29,290	43,371
Other accruals and reserves	14,409	17,924
Tax credit carryforwards	12,177	7,873
Depreciation	671	628
Total deferred tax assets before deferred liabilities	82,551	106,456
Valuation allowance	(22,780)	(18,189)
Deferred tax assets, net of valuation allowance	59,771	88,267
Purchased intangibles and other	(10,678)	(17,459)
Depreciation	(12,277)	(16,893)
Other accruals and reserves	(3,410)	(676)
Total deferred tax liabilities	(26,365)	(35,028)
Net deferred tax assets	$ 33,406	$ 53,239

Income Taxes (Schedule Of Recon

Income Taxes (Schedule Of Reconciliation Of Beginning And Ending Amount Of Unrecognized Tax Benefits) (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance, beginning of period	$ 23,135	$ 13,687	$ 9,562
Gross increases related to prior period tax positions	2,715	2,769	1,622
Gross decreases related to prior period tax positions	0	0	(7)
Gross increases related to current period tax positions	8,230	8,507	4,441
Decreases relating to settlements with tax authorities	0	(240)	(521)
Reductions due to lapses of statute of limitations	(2,408)	(1,588)	(1,410)
Balance, end of period	$ 31,672	$ 23,135	$ 13,687

Stock-Based Compensation (Narra

Stock-Based Compensation (Narrative) (Details) - USD ($)	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Jun. 30, 2014	Mar. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock option expiration period from date of grant	10 years
Share-based compensation award, offering period	6 months	6 months	6 months
Stock options issued during period	0
Total intrinsic value of options exercised	$ 100,000	$ 1,000,000	$ 1,900,000
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	1 year
Restricted stock units vesting period in years	1 year
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	4 years
Restricted stock units vesting period in years	4 years
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 126.86	$ 134.35	$ 109.65
Award vesting period	2 years	2 years	2 years
Restricted stock units vesting period in years	2 years	2 years	2 years
Fair market value of restricted stock vested	$ 182,600,000	$ 176,800,000	$ 137,700,000
Two Thousand Fourteen Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate of stock options and awards upon certain changes in ownership control	50.00%
Common stock reserved for issuance	18,730,000
Shares available for award	2,051,687
Two Thousand Fourteen Equity Incentive Plan [Member] | Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 119.01	$ 121.44
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	62,396
Stock units issued	62,396
Outstanding stock units	24,079	13,871
Two Thousand Fourteen Equity Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 129.35	$ 127.89
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	1,307,589
Stock units issued	1,307,589
Outstanding stock units	1,150,870	1,347,431
Defense.Net, Inc. 2012 Stock Option and Grant Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for purchase under stock option plan	113
Common stock reserved for issuance				84,375
Traffix 2007 Plan [Member] [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares available for purchase under stock option plan	49
Common stock reserved for issuance					106,829
Two Thousand Eleven Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for issuance	8,000,000
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
Share-based compensation award, offering period	6 months
Percentage of common stock lesser of the fair market value	85.00%
Shares available for award	652,351

Stock-Based Compensation (Sched

Stock-Based Compensation (Schedule Of Summary Of Restricted Stock Unit Activity) (Details)	12 Months Ended
	Sep. 30, 2018$ / sharesshares
Performance Shares [Member] | Two Thousand Fourteen Equity Incentive Plan [Member]
Outstanding Restricted Stock Units
Outstanding Stock Units, Beginning balance | shares	13,871
Outstanding Stock Units, Units granted | shares	62,396
Outstanding Stock Units, Units vested | shares	(24,374)
Outstanding Stock Units, Units cancelled | shares	(27,814)
Outstanding Stock Units, Ending balance | shares	24,079
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning balance	$ 121.44
Weighted Average Grant Date Fair Value, Units granted	118.97
Weighted Average Grant Date Fair Value, Units vested	145.23
Weighted Average Grant Date Fair Value, Units cancelled	119.15
Weighted Average Grant Date Fair Value, Ending balance	119.01
Restricted Stock Units (RSUs) [Member]
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning balance	134.35
Weighted Average Grant Date Fair Value, Ending balance	$ 126.86
Restricted Stock Units (RSUs) [Member] | Two Thousand Fourteen Equity Incentive Plan [Member]
Outstanding Restricted Stock Units
Outstanding Stock Units, Beginning balance | shares	1,347,431
Outstanding Stock Units, Units granted | shares	1,307,589
Outstanding Stock Units, Units vested | shares	(1,191,577)
Outstanding Stock Units, Units cancelled | shares	(312,573)
Outstanding Stock Units, Ending balance | shares	1,150,870
Weighted Average Grant Date Fair Value
Weighted Average Grant Date Fair Value, Beginning balance	$ 127.89
Weighted Average Grant Date Fair Value, Units granted	127.24
Weighted Average Grant Date Fair Value, Units vested	150.75
Weighted Average Grant Date Fair Value, Units cancelled	125.46
Weighted Average Grant Date Fair Value, Ending balance	$ 129.35

Stock-Based Compensation (Sch_2

Stock-Based Compensation (Schedule Of Stock Option Activity) (Details)	12 Months Ended
	Sep. 30, 2018$ / sharesshares
Number of Shares
Number of Shares, Beginning balance | shares	976
Number of Shares, Options granted | shares	0
Number of Shares, Options exercised | shares	(814)
Number of Shares, Options cancelled | shares	0
Number of Shares, Ending balance | shares	162
Weighted Average Exercise Price per Share
Weighted Average Exercise Price per Share, Beginning balance | $ / shares	$ 3.18
Weighted Average Exercise Price per Share, Options granted | $ / shares	0
Weighted Average Exercise Price per Share, Options exercised | $ / shares	3.07
Weighted Average Exercise Price per Share, Options cancelled | $ / shares	0
Weighted Average Exercise Price per Share, Ending balance | $ / shares	$ 3.76

Stock-Based Compensation (Sch_3

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, 2018	Sep. 30, 2017
Share-based Compensation [Abstract]
Stock options outstanding	162	976
Stock options outstanding, Weighted Average Remaining Contractual Life (in Years)	4 years 266 days
Stock options outstanding, Weighted Average Exercise Price per Share	$ 3.76	$ 3.18
Stock options outstanding, Aggregate Intrinsic Value	$ 32
Exercisable, Number of Shares	162
Exercisable, Weighted Average Remaining Contractual Life (in Years)	4 years 266 days
Exercisable, Weighted Average Exercise Price per Share	$ 3.76
Exercisable, Aggregate Intrinsic Value	$ 32
Vested and expected to vest, Number of Shares	162
Vested and expected to vest, Weighted Average Remaining Contractual Life (in Years)	4 years 266 days
Vested and expected to vest, Weighted Average Exercise Price per Share	$ 3.76
Vested and expected to vest, Aggregate Intrinsic Value	$ 32

Stock-Based Compensation (Sch_4

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, 2018shares
Awards Available for Grant
Awards Available for Grant, Beginning balance	3,081,285
Awards Available for Grant, Granted	(1,369,985)
Awards Available for Grant, Cancelled	341,000
Additional shares reserved (terminated), net	(613)
Awards Available for Grant, Ending balance	2,051,687

Commitments And Contingencies (

Commitments And Contingencies (Narrative) (Details) ft² in Thousands, $ in Millions	1 Months Ended	12 Months Ended
	Oct. 31, 2006ft²	Sep. 30, 2018USD ($)ft²building	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)
Commitments And Contingencies [Line Items]
Number of buildings in the amended and restated lease | building		4
Lease expiration date		Dec. 31, 2022
Rent expense under non-cancelable operating leases | $		$ 30	$ 30.2	$ 30.1
Contract manufacturers' purchase obligations | $		$ 26.2
333 Elliott West [Member]
Commitments And Contingencies [Line Items]
Office space in a building for which lease agreement is entered | ft²	137
F5 Tower [Member]
Commitments And Contingencies [Line Items]
Office space in a building for which lease agreement is entered | ft²		515
Lessee, Operating Lease, Term of Contract		14 years 6 months
Earliest Commencement of Lease		Apr. 1, 2019
Time After Substantial Completion Date of Construction Latest Date for Commencement of Lease		10 months
Pending Litigation [Member] | F5 Counterclaim of Radware, Ltd. and Radware, Inc. Patent Infringement Complaint [Member]
Commitments And Contingencies [Line Items]
Gain Contingency, Patents Allegedly Infringed upon, Number		3

Commitments And Contingencies_2

Commitments And Contingencies (Schedule Of Future Minimum Operating Lease Payments, Net Of Sublease Income) (Details) $ in Thousands	Sep. 30, 2018USD ($)
Gross Lease Payments
Gross Lease Payments, 2019	$ 30,870
Gross Lease Payments, 2020	45,418
Gross Lease Payments, 2021	42,615
Gross Lease Payments, 2022	40,285
Gross Lease Payments, 2023	31,238
Gross Lease Payments, Thereafter	271,882
Gross Lease Payments, Total	462,308
Sublease Income
Sublease Income, 2019	0
Sublease Income, 2020	0
Sublease Income, 2021	0
Sublease Income, 2022	0
Sublease Income, 2023	0
Sublease Income, Thereafter	0
Sublease Income, Total	0
Net Lease Payments
Net Lease Payments, 2019	30,870
Net Lease Payments, 2020	45,418
Net Lease Payments, 2021	42,615
Net Lease Payments, 2022	40,285
Net Lease Payments, 2023	31,238
Net Lease Payments, Thereafter	271,882
Net Lease Payments, Total	$ 462,308

Restructuring Charges (Details)

Restructuring Charges (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2018USD ($)employee	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)
Restructuring and Related Activities [Abstract]
Number of employees affected | employee									215
Restructuring charges	$ 18,426	$ 0	$ 0	$ 0	$ 12,718	$ 0	$ 0	$ 0	$ 18,426	$ 12,718	$ 0
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning of the period				7,741					7,741
Restructuring charges	18,426	$ 0	$ 0	$ 0	12,718	$ 0	$ 0	$ 0	18,426	12,718	$ 0
Cash payments									(17,899)
Non-cash items									0
Restructuring reserve, end of the period	$ 8,268				$ 7,741				$ 8,268	$ 7,741

Employee Benefit Plans (Details

Employee Benefit Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]
Contributions by the Company to the plan	$ 10.5	$ 10.5	$ 9.5
Employer contribution, vesting period	4 years

Geographic Sales And Signific_3

Geographic Sales And Significant Customers (Details) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2018USD ($)	Jun. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2017USD ($)	Sep. 30, 2017USD ($)	Jun. 30, 2017USD ($)	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2018USD ($)segmentgeographic_region	Sep. 30, 2017USD ($)	Sep. 30, 2016USD ($)
Segment Reporting Information [Line Items]
Number of Reportable Segments | segment									1
Number of Geographic Regions | geographic_region									4
Revenue	$ 562,709	$ 542,203	$ 533,304	$ 523,191	$ 537,998	$ 517,837	$ 518,248	$ 515,958	$ 2,161,407	$ 2,090,041	$ 1,995,034
Property and equipment, net	145,042				122,420				145,042	122,420
United States [Member]
Segment Reporting Information [Line Items]
Revenue									1,088,270	1,075,222	1,019,054
Property and equipment, net	126,790				103,486				126,790	103,486
Other Americas [Member]
Segment Reporting Information [Line Items]
Revenue									116,073	110,298	106,228
Americas [Member]
Segment Reporting Information [Line Items]
Revenue									1,204,343	1,185,520	1,125,282
EMEA [Member]
Segment Reporting Information [Line Items]
Revenue									546,239	506,571	487,966
Property and equipment, net	12,538				15,054				12,538	15,054
Japan [Member]
Segment Reporting Information [Line Items]
Revenue									95,251	95,055	94,767
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Revenue									315,574	302,895	$ 287,019
Other International Countries [Member]
Segment Reporting Information [Line Items]
Property and equipment, net	$ 5,714				$ 3,880				$ 5,714	$ 3,880
Customer One [Member] | Geographic Concentration Risk [Member] | Sales Revenue, Net [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage									16.60%	16.10%	14.90%
Customer Two [Member] | Geographic Concentration Risk [Member] | Sales Revenue, Net [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage									11.60%	12.40%	13.30%
Customer Three [Member] | Geographic Concentration Risk [Member] | Sales Revenue, Net [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage									10.80%	0.00%	0.00%
Customer Four [Member] | Geographic Concentration Risk [Member] | Sales Revenue, Net [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage									10.70%	10.40%	10.10%
Customer Five [Member] | Geographic Concentration Risk [Member] | Sales Revenue, Net [Member]
Segment Reporting Information [Line Items]
Concentration risk percentage									10.40%	17.70%	18.70%

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, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Quarterly Financial Data [Abstract]
Products	$ 256,412	$ 238,835	$ 237,558	$ 227,303	$ 248,990	$ 235,109	$ 241,080	$ 239,483	$ 960,108	$ 964,662	$ 944,469
Services	306,297	303,368	295,746	295,888	289,008	282,728	277,168	276,475	1,201,299	1,125,379	1,050,565
Total	562,709	542,203	533,304	523,191	537,998	517,837	518,248	515,958	2,161,407	2,090,041	1,995,034
Products	48,505	45,164	44,127	43,265	46,641	43,787	43,928	41,676	181,061	176,032	166,624
Services	44,935	45,845	45,518	44,122	43,900	45,983	43,984	43,586	180,420	177,453	170,581
Total	93,440	91,009	89,645	87,387	90,541	89,770	87,912	85,262	361,481	353,485	337,205
Gross profit	469,269	451,194	443,659	435,804	447,457	428,067	430,336	430,696	1,799,926	1,736,556	1,657,829
Sales and marketing	160,425	165,806	169,970	167,934	162,068	160,952	164,705	164,514	664,135	652,239	628,743
Research and development	95,078	94,061	91,056	85,889	85,479	88,602	89,234	87,050	366,084	350,365	334,227
General and administrative	41,748	39,374	39,276	39,984	37,832	39,368	38,009	41,678	160,382	156,887	138,431
Litigation expense	0	0	0	0	525	1	(135)	0	0	391	9,051
Restructuring charges	18,426	0	0	0	12,718	0	0	0	18,426	12,718	0
Total	315,677	299,241	300,302	293,807	298,622	288,923	291,813	293,242	1,209,027	1,172,600	1,110,452
Income from operations	153,592	151,953	143,357	141,997	148,835	139,144	138,523	137,454	590,899	563,956	547,377
Other income, net	5,667	2,259	2,790	2,145	5,027	2,589	1,302	2,643	12,861	11,561	2,514
Income before income taxes	159,259	154,212	146,147	144,142	153,862	141,733	139,825	140,097	603,760	575,517	549,891
Provision for income taxes	26,378	31,469	36,511	55,713	18,119	44,071	46,687	45,879	150,071	154,756	184,036
Net income	$ 132,881	$ 122,743	$ 109,636	$ 88,429	$ 135,743	$ 97,662	$ 93,138	$ 94,218	$ 453,689	$ 420,761	$ 365,855
Net income per share - basic (USD per share)	$ 2.20	$ 2.01	$ 1.79	$ 1.42	$ 2.15	$ 1.53	$ 1.44	$ 1.45	$ 7.41	$ 6.56	$ 5.43
Weighted average shares - basic (shares)	60,462	60,970	61,420	62,195	63,088	63,935	64,479	65,195	61,262	64,173	67,433
Net income per share - diluted (USD per share)	$ 2.18	$ 1.99	$ 1.77	$ 1.41	$ 2.14	$ 1.52	$ 1.43	$ 1.44	$ 7.32	$ 6.50	$ 5.38
Weighted average shares - diluted (shares)	61,070	61,633	62,059	62,550	63,446	64,361	65,028	65,645	62,013	64,775	67,984

Subsequent Events (Details)

Subsequent Events (Details) - USD ($)	Oct. 31, 2018	Sep. 30, 2018	Oct. 25, 2017	Apr. 20, 2016
Subsequent Event [Line Items]
Stock repurchase program, remaining authorized repurchase amount		$ 573,600,000
October 26, 2010 Program [Member]
Subsequent Event [Line Items]
Stock repurchase program, authorized amount			$ 1,000,000,000	$ 3,400,000,000
October 26, 2010 Program [Member] | Subsequent Event [Member]
Subsequent Event [Line Items]
Stock repurchase program, authorized amount	$ 1,000,000,000