F5 (FFIV) 10-K 22 Nov 13 2013 FY Annual report Financial data

Document_And_Entity_Informatio

Document And Entity Information (USD $)	12 Months Ended
	Sep. 30, 2013	Nov. 15, 2013	Mar. 28, 2013
Document And Entity Information [Abstract]	'	'	'
Entity Registrant Name	'F5 NETWORKS INC	'	'
Entity Central Index Key	'0001048695	'	'
Current Fiscal Year End Date	'--09-30	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Document Type	'10-K	'	'
Document Period End Date	30-Sep-13	'	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'
Amendment Flag	'false	'	'
Entity Common Stock, Shares Outstanding	'	77,608,639	'
Entity Well-known Seasoned Issuer	'Yes	'	'
Entity Voluntary Filers	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Public Float	'	'	$6,962,311,879

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Sep. 30, 2013	Sep. 30, 2012
In Thousands, unless otherwise specified
ASSETS	'	'
Cash and cash equivalents	$189,693	$211,181
Short-term investments	352,450	320,970
Accounts receivable, net of allowances of $3,259 and $3,254	204,205	185,172
Inventories	19,026	17,410
Deferred tax assets	16,342	10,362
Other current assets	34,655	30,986
Total current assets	816,371	776,081
Property and equipment, net	63,522	59,604
Long-term investments	728,981	662,803
Deferred tax assets	22,389	35,478
Goodwill	523,727	348,239
Other assets, net	75,564	28,996
Total assets	2,230,554	1,911,201
LIABILITIES AND SHAREHOLDERS’ EQUITY	'	'
Accounts payable	37,313	27,026
Accrued liabilities	92,608	86,409
Deferred revenue	421,429	352,594
Total current liabilities	551,350	466,029
Other long-term liabilities	25,202	21,078
Deferred revenue, long-term	109,944	94,694
Deferred tax liabilities	5,346	0
Total long-term liabilities	140,492	115,772
Commitments and contingencies (Note 8)	'	'
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, 78,090 and 78,715 shares issued and outstanding	262,505	326,922
Accumulated other comprehensive loss	-7,414	-3,829
Retained earnings	1,283,621	1,006,307
Total shareholders’ equity	1,538,712	1,329,400
Total liabilities and shareholders’ equity	$2,230,554	$1,911,201

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2013	Sep. 30, 2012
In Thousands, except Per Share data, unless otherwise specified
Statement of Financial Position [Abstract]	'	'
Accounts receivable, allowances	$3,259	$3,254
Preferred stock, par value (USD per share)	$0	$0
Preferred stock, shares authorized	10,000	10,000
Preferred stock, shares outstanding	0	0
Common stock, par value (USD per share)	$0	$0
Common stock, shares authorized	200,000	200,000
Common stock, shares issued	78,090	78,715
Common stock, shares outstanding	78,090	78,715

Consolidated_Income_Statements

Consolidated Income Statements (USD $)	1 Months Ended	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Aug. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Net revenues	'	'	'	'	'	'	'	'	'	'	'	'
Products	'	$212,291	$196,746	$185,107	$204,712	$209,718	$207,118	$205,165	$196,554	$798,856	$818,555	$721,975
Services	'	183,038	173,556	165,125	160,739	152,841	145,516	134,457	125,878	682,458	558,692	429,859
Total	'	395,329	370,302	350,232	365,451	362,559	352,634	339,622	322,432	1,481,314	1,377,247	1,151,834
Cost of net revenues	'	'	'	'	'	'	'	'	'	'	'	'
Products	'	35,151	32,350	29,773	31,792	35,752	34,482	33,668	33,200	129,066	137,102	129,325
Services	'	31,792	32,567	30,529	29,093	26,929	25,805	23,926	22,406	123,981	99,066	78,679
Total	'	66,943	64,917	60,302	60,885	62,681	60,287	57,594	55,606	253,047	236,168	208,004
Gross profit	'	328,386	305,385	289,930	304,566	299,878	292,347	282,028	266,826	1,228,267	1,141,079	943,830
Operating expenses	'	'	'	'	'	'	'	'	'	'	'	'
Sales and marketing	'	119,836	121,906	119,031	122,268	116,298	112,064	110,995	106,238	483,041	445,595	370,735
Research and development	'	54,464	54,075	52,534	48,541	47,731	46,985	43,568	39,122	209,614	177,406	138,910
General and administrative	'	26,512	25,327	25,889	24,673	24,015	23,298	22,785	21,677	102,401	91,775	83,523
Loss on facility sublease	2,393	2,393	0	0	0	0	0	0	0	2,393	0	0
Total	'	203,205	201,308	197,454	195,482	188,044	182,347	177,348	167,037	797,449	714,776	593,168
Income from operations	'	125,181	104,077	92,476	109,084	111,834	110,000	104,680	99,789	430,818	426,303	350,662
Other income, net	'	732	2,874	2,118	1,550	909	1,713	1,428	1,861	7,274	5,911	10,089
Income before income taxes	'	125,913	106,951	94,594	110,634	112,743	111,713	106,108	101,650	438,092	432,214	360,751
Provision for income taxes	'	49,682	38,773	31,182	41,141	45,026	39,377	37,467	35,158	160,778	157,028	119,354
Net income	'	$76,231	$68,178	$63,412	$69,493	$67,717	$72,336	$68,641	$66,492	$277,314	$275,186	$241,397
Net income per share - basic (USD per share)	'	$0.97	$0.87	$0.81	$0.88	$0.86	$0.91	$0.87	$0.84	$3.53	$3.48	$2.99
Weighted average shares - basic (shares)	'	78,353	78,516	78,601	78,789	78,980	79,135	79,156	79,272	78,565	79,135	80,658
Net income per share - diluted (USD per share)	'	$0.97	$0.86	$0.80	$0.88	$0.85	$0.91	$0.86	$0.83	$3.50	$3.45	$2.96
Weighted average shares - diluted (shares)	'	78,674	78,864	79,114	79,278	79,425	79,655	79,775	79,822	79,136	79,780	81,482

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income Statement (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Statement of Other Comprehensive Income [Abstract]	'	'	'
Net income	$277,314	$275,186	$241,397
Foreign currency transaction adjustment	-2,407	295	-2,366
Unrealized (loss) gain on securities, net of taxes of $692, $(1,350) and $472 for the years ended September 30, 2013, 2012 and 2011, respectively	-1,178	2,298	-815
Total other comprehensive (loss) income	-3,585	2,593	-3,181
Comprehensive income	$273,729	$277,779	$238,216

Consolidated_Statements_of_Com1

Consolidated Statements of Comprehensive Income (Parentheticals) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Statement of Other Comprehensive Income [Abstract]	'	'	'
Tax effect of unrealized gain (loss) on securities	$692	($1,350)	$472

Consolidated_Statement_Of_Shar

Consolidated Statement Of Shareholders' Equity And Comprehensive Income (USD $)	Total	Common Stock [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]	Retained Earnings [Member]
In Thousands, except Share data
Balance at Sep. 30, 2010	$1,003,698	$517,215	($3,241)	$489,724
Balance, shares at Sep. 30, 2010	'	80,355,000	'	'
Exercise of employee stock options	2,293	2,293	'	'
Exercise of employee stock options, shares	'	150,000	'	'
Issuance of stock under employee stock purchase plan	18,932	18,932	'	'
Issuance of stock under employee stock purchase plan, shares	'	257,000	'	'
Issuance of restricted stock, shares	'	1,370,000	'	'
Repurchase of common stock	-271,526	-271,526	'	'
Repurchase of common stock, shares	'	-2,987,000	'	'
Tax benefit from employee stock transactions	24,076	24,076	'	'
Stock-based compensation	89,747	89,747	'	'
Net income	241,397	'	'	241,397
Other comprehensive loss	-3,181	'	-3,181	'
Balance at Sep. 30, 2011	1,105,436	380,737	-6,422	731,121
Balance, shares at Sep. 30, 2011	'	79,145,000	'	'
Exercise of employee stock options	1,130	1,130	'	'
Exercise of employee stock options, shares	'	120,000	'	'
Issuance of stock under employee stock purchase plan	24,043	24,043	'	'
Issuance of stock under employee stock purchase plan, shares	'	281,000	'	'
Issuance of restricted stock, shares	'	832,000	'	'
Repurchase of common stock	-184,776	-184,776	'	'
Repurchase of common stock, shares	'	-1,663,000	'	'
Tax benefit from employee stock transactions	10,440	10,440	'	'
Stock-based compensation	95,348	95,348	'	'
Net income	275,186	'	'	275,186
Other comprehensive loss	2,593	'	2,593	'
Balance at Sep. 30, 2012	1,329,400	326,922	-3,829	1,006,307
Balance, shares at Sep. 30, 2012	78,715,000	78,715,000	'	'
Exercise of employee stock options	1,341	1,341	'	'
Exercise of employee stock options, shares	125,701	126,000	'	'
Issuance of stock under employee stock purchase plan	28,251	28,251	'	'
Issuance of stock under employee stock purchase plan, shares	'	422,000	'	'
Issuance of restricted stock, shares	'	1,094,000	'	'
Repurchase of common stock	-200,000	-200,000	'	'
Repurchase of common stock, shares	'	-2,267,000	'	'
Tax benefit from employee stock transactions	1,779	1,779	'	'
Stock-based compensation	104,212	104,212	'	'
Net income	277,314	'	'	277,314
Other comprehensive loss	-3,585	'	-3,585	'
Balance at Sep. 30, 2013	$1,538,712	$262,505	($7,414)	$1,283,621
Balance, shares at Sep. 30, 2013	78,090,000	78,090,000	'	'

Consolidated_Statements_Of_Cas

Consolidated Statements Of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Operating activities	'	'	'
Net income	$277,314	$275,186	$241,397
Adjustments to reconcile net income to net cash provided by operating activities:	'	'	'
Realized (gain) loss on disposition of assets and investments	-187	546	-163
Stock-based compensation	104,212	95,348	89,747
Provisions for doubtful accounts and sales returns	1,025	1,572	982
Depreciation and amortization	40,005	35,139	20,887
Deferred income taxes	474	-4,293	4,487
Changes in operating assets and liabilities, net of amounts acquired:	'	'	'
Accounts receivable	-18,867	-20,207	-54,526
Inventories	-1,617	-262	1,666
Other current assets	-3,614	-998	8,000
Other assets	683	-134	81
Accounts payable and accrued liabilities	16,790	9,953	20,476
Deferred revenue	83,475	103,587	83,904
Net cash provided by operating activities	499,693	495,437	416,938
Investing activities	'	'	'
Purchases of investments	-938,571	-1,059,853	-979,597
Maturities of investments	613,927	784,601	795,142
Sales of investments	212,011	81,444	80,877
(Increase) decrease in restricted cash	-612	-19	19
Acquisition of intangible assets	0	-250	-5,715
Acquisition of businesses, net of cash acquired	-212,642	-128,335	0
Purchases of property and equipment	-26,583	-29,867	-30,445
Net cash used in investing activities	-352,470	-352,279	-139,719
Financing activities	'	'	'
Excess tax benefit from stock-based compensation	4,091	10,371	23,623
Proceeds from the exercise of stock options and purchases of stock under employee stock purchase plan	29,591	25,174	21,239
Repurchase of common stock	-200,000	-184,776	-271,526
Net cash used in financing activities	-166,318	-149,231	-226,664
Net (decrease) increase in cash and cash equivalents	-19,095	-6,073	50,555
Effect of exchange rate changes on cash and cash equivalents	-2,393	470	-2,525
Cash and cash equivalents, beginning of year	211,181	216,784	168,754
Cash and cash equivalents, end of year	189,693	211,181	216,784
Supplemental information	'	'	'
Cash paid for taxes	$156,833	$145,874	$84,753

Summary_Of_Significant_Account

Summary Of Significant Accounting Policies

12 Months Ended

Sep. 30, 2013

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 delivery services. The Company’s core technology is a full-proxy, programmable, highly-scalable software platform called TMOS, which supports the industry’s broadest array of features and functions designed to ensure that applications delivered over Internet Protocol (IP) networks are secure, fast and available. The Company’s TMOS-based 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. These products are available as modules 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, or as software-only Virtual Editions designed to run on standard servers and major hypervisors. During fiscal year 2013, the Company acquired LineRate Systems, Inc. (LineRate Systems), an early-stage developer of software-defined application services that complement its current offerings, and Versafe Ltd. (Versafe), which offers subscription services that protect communications between end-user devices and web and mobile applications. In connection with its products, the Company offers a broad range of services including consulting, training, installation, maintenance and other technical support services.

Accounting Principles

The Company’s consolidated financial statements and accompanying notes are prepared on the accrual basis of accounting in accordance with generally accepted accounting principles in the United States of America (GAAP).

Principles of Consolidation

The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.

Reclassifications

In Note 6, Income Taxes, certain prior year amounts have been reclassified to conform to the current year presentation. There was no change to the total amount of income tax expense or net deferred tax asset as a result of the reclassifications.

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 four 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 and United States government and agency 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, 2013, Ingram Micro, Inc. accounted for 18.6% of the Company’s accounts receivable. At September 30, 2012, Avnet Technology Solutions and Ingram Micro, Inc. accounted for 13.4% and 12.0% of the Company’s accounts receivable, respectively.

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 or market (as determined by the first-in, first-out method).

Inventories consist of the following (in thousands):

September 30,

2013

2012

Finished goods

$

13,509

$

13,565

Raw materials

5,517

3,845

$

19,026

$

17,410

Property and Equipment

Property and equipment is stated at cost. 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 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,

2013

2012

Computer equipment

$

93,326

$

95,987

Office furniture and equipment

13,391

12,335

Leasehold improvements

54,972

43,957

161,689

152,279

Accumulated depreciation and amortization

(98,167

)

(92,675

)

$

63,522

$

59,604

Depreciation and amortization expense totaled approximately $22.3 million, $19.0 million, and $16.6 million for the fiscal years ended September 30, 2013, 2012 and 2011, 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 the acquisition of Versafe Ltd. in September 2013, LineRate Systems, Inc. in February 2013, Traffix Systems in fiscal year 2012, Acopia Networks, Inc. in fiscal year 2007, Swan Labs, Inc. in fiscal year 2006, MagniFire Websystems, Inc. in fiscal year 2004 and uRoam, Inc. in fiscal year 2003. For its annual goodwill impairment test, the Company operates under one reporting unit and the fair value of its reporting unit is 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 first performs a qualitative assessment to determine whether further impairment testing is necessary. 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.

Examples of events and circumstances that might indicate that a 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 an expectation that a reporting unit will be sold or a sustained decrease in the stock price on either an absolute basis or relative to peers.

If it is determined, as a result of the qualitative assessment, that it is more-likely-than-not that the fair value of the Company’s reporting unit is less than its carrying amount, the provisions of authoritative guidance require that the Company perform a two-step impairment test on goodwill. The first step of the test identifies whether potential impairment may have occurred, while the second step of the test measures the amount of the impairment, if any. Impairment is recognized when the carrying amount of goodwill exceeds its fair value. In March 2013, the Company completed a qualitative assessment of potential impairment indicators and concluded that it was more-likely-than-not that the fair value of its reporting unit exceeded its carrying amount. The Company also considered potential impairment indicators at September 30, 2013 and noted no indicators of impairment.

Other Assets

Other assets primarily consist of acquired and developed technology, software development costs and customer relationships.

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. IPR&D was recorded in connection with the acquisition of LineRate Systems, Inc. in February 2013.

Acquired and developed technology is recorded at cost and amortized over its estimated useful life of five years. The estimated useful life of these assets is assessed and evaluated for reasonableness periodically. Acquired technology of $15.4 million in fiscal year 2013 and $14.9 million in fiscal 2012 was recorded in connection with the acquisitions of Versafe and Traffix Systems, respectively. Amortization expense related to acquired technology, which is charged to cost of product revenues, totaled $3.8 million, $5.3 million and $3.1 million during the fiscal years 2013, 2012 and 2011, respectively.

Software development costs are charged to research and development expense in the period incurred until technological feasibility is established. Thereafter, until the product is released for sale, software development costs are capitalized and reported at the lower of unamortized cost or net realizable value of each product. 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 did not capitalize any software development costs in fiscal years 2013, 2012 and 2011. Amortization expense related to capitalized software development was immaterial for fiscal years 2013, 2012, and 2011.

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 recovery 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 2013, 2012 and 2011.

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 year ended September 30, 2013.

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. In certain regions where the Company does not have the ability to reasonably estimate returns, the Company defers revenue on sales to its distributors until information is received from the channel partner indicating that the product has been sold to the end-user customer. 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. The Company offers extended payment terms to certain customers, in which case, revenue is recognized when payments are due.

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 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 its 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, 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, 2013, 2012 and 2011 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 statements of income as incurred.

Advertising

Advertising costs are expensed as incurred. The Company incurred $2.8 million, $1.8 million and $2.2 million in advertising costs during the fiscal years 2013, 2012 and 2011, 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 Ltd. in the United Kingdom and F5 Networks (Israel) Ltd., Traffix Communication Systems Ltd. and Versafe Ltd. in 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. The net effect of foreign currency gains and losses was not significant during the fiscal years ended September 30, 2013, 2012 and 2011.

Segments

Management has determined that the Company was organized as, and operated in, one reportable operating segment for fiscal year 2013 and prior years: the development, marketing and sale of application delivery networking products 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 $104.2 million, $95.3 million and $89.7 million of stock-based compensation expense for the fiscal years ended September 30, 2013, 2012 and 2011, respectively. As of September 30, 2013, there was $82.5 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 29, 2013, the Company’s Compensation Committee approved 1,467,871 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. All stock options granted in fiscal years 2013 and 2012 were assumed as part of the acquisitions of LineRate Systems and Traffix Systems, respectively, in the second fiscal quarter of each year. No stock options were granted in fiscal year 2011. 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

Years Ended September 30,

2013

2012

2011

Risk-free interest rate

0.06

%

0.14

%

0.1

%

Expected dividend

—

—

—

Expected term

0.5 years

0.5 years

0.5 years

Expected volatility

42.92

%

45.2

%

53.87

%

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 estimated forfeiture rate for grants awarded to the Company’s executive officers and Board of Directors was approximately 7% and the estimated forfeiture rate for grants awarded to all other employees was approximately 8% in fiscal 2013. If the actual number of forfeitures differs from those estimated by management, additional adjustments to compensation expense may be required in future periods.

In November 2012, the Company granted 290,415 RSUs to certain current executive officers as part of the annual equity awards program. Fifty percent of the aggregate number of RSUs vest in equal quarterly increments over four years, until such portion of the grant is fully vested on November 1, 2016. One-eighth of the RSU grant, or a portion thereof, was subject to the Company achieving specified quarterly revenue and EBITDA goals during fiscal year 2013. In each case, 50% of the quarterly performance stock grant is based on achieving at least 80% of the quarterly revenue goal and the other 50% is based on achieving at least 80% of the quarterly EBITDA goal. The quarterly performance stock grant is paid linearly above 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 100% over-achievement threshold. The remaining 37.5% of this annual equity awards RSU grant shall be subject to quarterly performance based vesting for fiscal years 2014, 2015 and 2016 (12.5% in each period). The Compensation Committee of the Board of Directors will set applicable performance targets and vesting formulas for each of these periods.

In November 2011, as part of the annual review of executive compensation by the Compensation Committee of the Board of Directors and a change in the grant date for the Company’s annual equity awards program for the executive officers from August 1 to November 1, the Company granted 82,968 RSUs to certain current executive officers. Fifty percent of the aggregate number of RSUs vest in equal quarterly increments over three years, until such portion of the grant is fully vested on November 1, 2014. One-sixth of the RSU grant, or a portion thereof, was subject to the Company achieving specified quarterly revenue and EBITDA goals during fiscal year 2012. The remaining 33.33% of this annual equity awards RSU grant shall be subject to quarterly performance based vesting for fiscal years 2013 and 2014 (16.66% in each period). The Compensation Committee of the Board of Directors will set applicable performance targets and vesting formulas for each of these periods.

In August 2011, the Company granted 170,390 RSUs to certain current executive officers as part of the annual equity awards program. Fifty percent of the aggregate number of RSUs granted as part of the annual equity awards program vest in equal quarterly increments over three years, until such portion of the grant is fully vested on August 1, 2014. One-sixth of the annual equity awards RSU grant, or a portion thereof, was subject to the Company achieving specified quarterly revenue and EBITDA goals during the period beginning in the fourth quarter of fiscal year 2011 through the third quarter of fiscal year 2012. The remaining 33.33% of this annual equity awards RSU grant shall be subject to performance based vesting for each of the four quarter periods beginning with the fourth quarters of fiscal years 2012 and 2013 (16.66% in each period). The Compensation Committee of the Board of Directors will set applicable performance targets and vesting formulas for each of these periods.

In August 2010, the Company granted 181,334 and 83,000 RSUs to certain current executive officers as part of the annual equity and retention awards programs, respectively. Fifty percent of the aggregate number of RSUs granted as part of the annual equity awards program vested in equal quarterly increments over three years, until such portion of the grant was fully vested on August 1, 2013.

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 April 24, 2013, the Company announced that its Board of Directors authorized an additional $200 million for its common stock share repurchase program. This new authorization is incremental to the existing $600 million program, initially approved in October 2010 and expanded in August 2011 and October 2011. 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. As of November 15, 2013, the Company had repurchased and retired 12,289,015 shares at an average price of $72.18 per share and the Company had $112.5 million remaining to purchase shares as part of its repurchase programs.

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 awards and restricted stock units do not have nonforfeitable rights to dividends or dividend equivalents.

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,

2013

2012

2011

Numerator

Net income

$

277,314

$

275,186

$

241,397

Denominator

Weighted average shares outstanding — basic

78,565

79,135

80,658

Dilutive effect of common shares from stock options and restricted stock units

571

645

824

Weighted average shares outstanding — diluted

79,136

79,780

81,482

Basic net income per share

$

3.53

$

3.48

$

2.99

Diluted net income per share

$

3.5

$

3.45

$

2.96

An immaterial amount of common shares potentially issuable from stock options for the years ended September 30, 2013, 2012 and 2011 are excluded from the calculation of diluted earnings per share because the exercise price was greater than the average market price of common stock for the respective period.

Recent Accounting Pronouncements

In February 2013, the FASB issued ASU 2013-2, Comprehensive Income (Topic 220): Reporting of Amounts Reclassified out of Accumulated Other Comprehensive Income (ASU 2013-2), to improve the reporting of reclassifications out of accumulated other comprehensive income. ASU 2013-2 requires presentation, either on the face of the financial statements or in the notes, of amounts reclassified out of accumulated other comprehensive income by component and by net income line item. ASU 2013-2 is effective prospectively for fiscal years, and interim periods within those years, beginning after December 15, 2012. The Company will adopt ASU 2013-2 in the first quarter of fiscal 2014 and does not expect the adoption of this standard to have an impact on its consolidated financial statements.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Sep. 30, 2013
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 and U.S. government agency 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, 2013, were as follows (in thousands):
		Fair Value Measurements at Reporting Date Using								Fair Value at
										September 30,
		Quoted Prices in			Significant			Significant		2013
		Active Markets for			Other Observable			Unobservable
		Identical Securities			Inputs			Inputs
		(Level  1)			(Level 2)			(Level 3)
	Cash equivalents	$	13,145		$	—		$	—	$	13,145
	Short-term investments
	Available-for-sale securities — corporate bonds and notes	—			125,212			—		125,212
	Available-for-sale securities — municipal bonds and notes	—			72,164			—		72,164
	Available-for-sale securities — U.S. government securities	—			5,000			—		5,000
	Available-for-sale securities — U.S. government agency securities	—			150,074			—		150,074
	Long-term investments
	Available-for-sale securities — corporate bonds and notes	—			260,318			—		260,318
	Available-for-sale securities — municipal bonds and notes	—			24,371			—		24,371
	Available-for-sale securities — U.S. government securities	—			14,798			—		14,798
	Available-for-sale securities — U.S. government agency securities	—			426,458			—		426,458
	Available-for-sale securities — auction rate securities	—			—			3,036		3,036
	Total	$	13,145		$	1,078,395		$	3,036	$	1,094,576
	The Company’s financial assets measured at fair value on a recurring basis subject to the disclosure requirements at September 30, 2012, were as follows (in thousands):
		Fair Value Measurements at Reporting Date Using								Fair Value at
										September 30,
		Quoted Prices in			Significant			Significant		2012
		Active Markets for			Other Observable			Unobservable
		Identical Securities			Inputs			Inputs
		(Level 1)			(Level 2)			(Level 3)
	Cash equivalents	$	35,658		$	—		$	—	$	35,658
	Short-term investments
	Available-for-sale securities — certificates of deposit	—			3,533			—		3,533
	Available-for-sale securities — corporate bonds and notes	—			193,990			—		193,990
	Available-for-sale securities — municipal bonds and notes	—			63,422					63,422
	Available-for-sale securities — U.S. government agency securities	—			60,025			—		60,025
	Long-term investments
	Available-for-sale securities — corporate bonds and notes	—			229,441			—		229,441
	Available-for-sale securities — municipal bonds and notes	—			30,307			—		30,307
	Available-for-sale securities — U.S. government securities	—			4,995			—		4,995
	Available-for-sale securities — U.S. government agency securities	—			393,310			—		393,310
	Available-for-sale securities — auction rate securities	—			—			4,750		4,750
	Total	$	35,658		$	979,023		$	4,750	$	1,019,431
	Due to the auction failures of the Company’s auction rate securities (ARS) that began in the second quarter of fiscal year 2008, there are still no quoted prices in active markets for similar assets as of September 30, 2013. Therefore, the Company has classified its ARS as level 3 financial assets. The following table provides a reconciliation between the beginning and ending balances of items measured at fair value on a recurring basis in the tables above that used significant unobservable inputs (Level 3) (in thousands):
		2013			2012
	Balance, beginning of period	$	4,750		$	13,010
	Total (losses) gains realized or unrealized:
	Included in other comprehensive income	(14		)	1,740
	Settlements	(1,700		)	(10,000		)
	Balance, end of period	$	3,036		$	4,750
	Unrealized (losses) gains attributable to assets still held as of the end of the period	(14		)	112
	Financial assets are considered Level 3 when their fair values are determined using pricing models, discounted cash flow methodologies or similar techniques and at least one significant model assumption or input is unobservable or there is limited market activity such that the determination of fair value requires significant judgment or estimation. Level 3 investment securities primarily include certain ARS for which there was a decrease in the observation of market pricing. At September 30, 2013, the values of these securities were estimated primarily using discounted cash flow analysis that incorporated transaction details such as contractual terms, maturity, timing and amount of future cash flows, as well as assumptions about liquidity and credit valuation adjustments of marketplace participants at September 30, 2013. Significant fluctuations in any of these inputs in isolation would result in changes in the fair value of the Company’s ARS.
	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, 2013, the Company did not recognize any impairment charges related to goodwill, intangible assets, or long-lived assets.

ShortTerm_And_LongTerm_Investm

Short-Term And Long-Term Investments	12 Months Ended
	Sep. 30, 2013
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, 2013	Cost or		Gross			Gross			Fair Value
		Amortized		Unrealized			Unrealized
		Cost		Gains			Losses
	Corporate bonds and notes	$	125,010	$	210		$	(8	)	$	125,212
	Municipal bonds and notes	72,116		58			(10		)	72,164
	U.S. government securities	4,998		2			—			5,000
	U.S. government agency securities	150,069		15			(10		)	150,074
		$	352,193	$	285		$	(28	)	$	352,450
	September 30, 2012	Cost or		Gross			Gross			Fair Value
		Amortized		Unrealized			Unrealized
		Cost		Gains			Losses
	Certificates of deposit	$	3,528	$	5		$	—		$	3,533
	Corporate bonds and notes	193,548		482			(40		)	193,990
	Municipal bonds and notes	63,371		61			(10		)	63,422
	U.S. government agency securities	60,010		15			—			60,025
		$	320,457	$	563		$	(50	)	$	320,970
	Long-term investments consist of the following (in thousands):
	September 30, 2013	Cost or		Gross			Gross			Fair Value
		Amortized		Unrealized			Unrealized
		Cost		Gains			Losses
	Corporate bonds and notes	$	260,345	$	363		$	(390	)	$	260,318
	Municipal bonds and notes	24,332		44			(5		)	24,371
	Auction rate securities	3,300		—			(264		)	3,036
	U.S. government securities	14,755		43			—			14,798
	U.S. government agency securities	426,616		294			(452		)	426,458
		$	729,348	$	744		$	(1,111	)	$	728,981
	September 30, 2012	Cost or		Gross			Gross			Fair Value
		Amortized		Unrealized			Unrealized
		Cost		Gains			Losses
	Corporate bonds and notes	$	228,438	$	1,063		$	(60	)	$	229,441
	Municipal bonds and notes	30,177		138			(8		)	30,307
	Auction rate securities	5,000		—			(250		)	4,750
	U.S. government securities	4,983		12			—			4,995
	U.S. government agency securities	392,959		389			(38		)	393,310
		$	661,557	$	1,602		$	(356	)	$	662,803
	The amortized cost and fair value of fixed maturities at September 30, 2013, by contractual years-to-maturity, are presented below (in thousands):
	September 30, 2013	Cost or		Fair Value
		Amortized
		Cost
	One year or less	$	352,193	$	352,450
	Over one year	729,348		728,981
		$	1,081,541	$	1,081,431
	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, 2013 (in thousands):
		Less Than 12 Months					12 Months or Greater						Total
	September 30, 2013	Fair Value		Gross			Fair			Gross			Fair Value		Gross
				Unrealized			Value			Unrealized					Unrealized
				Losses						Losses					Losses
	Corporate bonds and notes	$	171,144	$	(397	)	$	3,181		$	(1	)	$	174,325	$	(398	)
	Municipal bonds and notes	20,080		(15		)	—			—			20,080		(15		)
	Auction rate securities	—		—			3,036			(264		)	3,036		(264		)
	U.S. government agency securities	317,773		(462		)	—			—			317,773		(462		)
	Total	$	508,997	$	(874	)	$	6,217		$	(265	)	$	515,214	$	(1,139	)
	The Company invests in securities that are rated investment grade or better. The unrealized losses on investments for fiscal year 2013 were primarily caused by reductions in the values of the ARS due to the illiquid markets and were partially offset by unrealized gains related to interest rate decreases.
	ARS are variable-rate debt securities. The Company limits its investments in ARS to securities that carry an AAA/A- (or equivalent) rating from recognized rating agencies and limits the amount of credit exposure to any one issuer. At the time of the Company’s initial investment and at the date of this report, all ARS were in compliance with the Company’s investment policy. In the past, the auction process allowed investors to obtain immediate liquidity if so desired by selling the securities at their face amounts. Liquidity for these securities has historically been provided by an auction process that resets interest rates on these investments on average every 7-35 days. However, as has been reported in the financial press, the disruptions in the credit markets adversely affected the auction market for these types of securities. The Company does not intend to sell nor is it more likely than not that it will be required to sell these investments before their anticipated recovery.
	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, 2013, there were no investments in its portfolio that were other-than-temporarily impaired.

Business_Combinations

Business Combinations	12 Months Ended
	Sep. 30, 2013
Business Combinations [Abstract]	'
Business Combinations	'
	Business Combinations
	The Company’s acquisitions are accounted for under the acquisition method. The total purchase price is allocated to the tangible and intangible assets acquired and the liabilities assumed based on their estimated fair values. The excess of the purchase price over those fair values is recorded as goodwill. The fair value assigned to the tangible and intangible assets acquired and liabilities assumed are based on estimates and assumptions provided by management. Goodwill is not amortized but instead is tested for impairment at least annually, as described in Note 1.
	Fiscal Year 2013 Acquisition of LineRate Systems, Inc.
	On February 11, 2013, the Company acquired all issued and outstanding shares of LineRate Systems, Inc. (LineRate Systems), a privately held Delaware corporation headquartered in Louisville, Colorado for $125.3 million. Direct transaction costs associated with the acquisition were approximately $0.3 million and were expensed as general and administrative expenses in the second quarter of fiscal 2013. LineRate Systems is a developer of software defined network service solutions for packet core operators, and cloud and web service providers. Through this acquisition, the Company gains access to LineRate Systems’ layer 7+ networking services technology, intellectual property, and engineering talent. As a result of the acquisition, the Company acquired all the assets and assumed all the liabilities of LineRate Systems. The results of operations of LineRate Systems have been included in the Company’s consolidated financial statements from the date of acquisition. Pro forma results of operations for this acquisition have not been presented as this transaction is not considered a material acquisition and the effects were not material to the Company’s financial results for the year ended September 30, 2013 individually or in aggregate with Versafe.
	The purchase price allocation is as follows (in thousands):
	Assets acquired
	Cash	$	82
	Current assets	556
	Property and equipment, net	415
	In-process research and development	29,853
	Goodwill	99,560
	Total assets acquired	$	130,466
	Liabilities assumed
	Accrued liabilities	$	(396	)
	Deferred tax liabilities, net	(4,763		)
	Total liabilities assumed	(5,159		)
	Net assets acquired	$	125,307
	Of the total estimated purchase price, $29.9 million was allocated to in-process research and development (IPR&D), which consists of existing research and development projects at the time of acquisition. IPR&D acquired from LineRate Systems is included in other assets, net on the balance sheet as of September 30, 2013. IPR&D assets are initially recognized at fair value and are classified as indefinite-lived assets until the successful completion or abandonment of the associated research and development efforts. Accordingly, during the development period after the acquisition date, this asset will not be amortized as charges to earnings; instead this asset will be subject to periodic impairment testing. Upon successful completion of the development process for the acquired IPR&D project, the asset would then be considered a finite-lived intangible asset and amortization of the asset will commence. The Company expects to complete the IPR&D project in 2014, at which point amortization will begin over its estimated useful life of ten years. To determine the fair value of IPR&D, the multi-period excess earnings method under the income approach was used, which included estimates and assumptions provided by LineRate Systems and Company management. The income approach estimates the fair value of an asset based on its earnings and cash flow capacity, which are discounted to present value. A discount rate of 35% was used to value the project based on the implied rate of return of the transaction, adjusted to reflect additional risks inherent in the acquired project. Goodwill generated from this transaction is primarily related to expected synergies, and is not expected to be deductible for federal tax purposes.
	The fair value of replacement stock-based compensation awards issued by the Company attributable to precombination services was immaterial and has not been reflected in the consideration transferred.
	Fiscal Year 2013 Acquisition of Versafe Ltd.
	On September 17, 2013, the Company acquired all issued and outstanding shares of Versafe Ltd. (Versafe), a privately held Israeli company headquartered in Rishon LeZion, Israel for $91.7 million. Direct transaction costs associated with the acquisition were approximately $0.4 million and were expensed as general and administrative expenses in the fourth quarter of fiscal 2013. Versafe is a provider of web anti-fraud, anti-phishing, and anti-malware solutions. Through this acquisition, the Company gains access to Versafe's web and mobile protection solutions and security operations center, their intellectual property and engineering talent. As a result of the acquisition, the Company acquired all the assets and assumed all the liabilities of Versafe. The results of operations of Versafe have been included in the Company’s consolidated financial statements from the date of acquisition. Pro forma results of operations for this acquisition have not been presented as this transaction is not considered a material acquisition and the effects were not material to the Company’s financial results for the year ended September 30, 2013 individually or in aggregate with LineRate Systems.
	The purchase price allocation is as follows (in thousands):
	Assets acquired
	Cash	$	4,020
	Current assets	1,309
	Property and equipment, net	41
	Developed technology, customer relationships and other intangibles	21,260
	Goodwill	75,937
	Total assets acquired	$	102,567
	Liabilities assumed
	Accrued liabilities	$	(4,877	)
	Deferred revenue	(611		)
	Deferred tax liabilities, net	(5,335		)
	Total liabilities assumed	(10,823		)
	Net assets acquired	$	91,744
	Of the total estimated purchase price, $15.4 million was allocated to developed technology and $5.9 million to customer relationships and other intangibles. To determine the fair value of developed technology, the multi-period excess earnings method under the income approach was used, which included estimates and assumptions provided by Versafe and Company management. The income approach estimates the fair value of an asset based on its earnings and cash flow capacity, which are discounted to present value. A discount rate of 25% was applied to the value of developed technology based on the implied rate of return of the transaction, adjusted to reflect additional risks and uncertainty in future cash flows. A combination of the income and cost approaches were used to determine the fair value of customer relationships and other intangibles. The cost approach requires an estimation of the costs required by a market participant to reproduce the asset. Goodwill generated from this transaction is primarily related to expected synergies of the technology and expanded breadth of the Company's existing security solutions. Goodwill and other intangibles associated with the Versafe transaction will not be deductible for Israeli tax purposes unless certain qualifications are met, and necessary rulings are obtained from the Israeli Tax Authority.
	Developed technology will be amortized on a straight-line basis over its estimated useful life of five years and included in cost of net product revenues. Customer relationships will be amortized on a straight-line basis over its estimated useful life of ten years and included in sales and marketing expenses. The weighted average life of the amortizable intangible assets recognized from the Versafe acquisition was 5.5 years. The estimated useful lives for the acquired intangible assets were based on the expected future cash flows associated with the respective asset.

Balance_Sheet_Details

Balance Sheet Details	12 Months Ended
	Sep. 30, 2013
Balance Sheet Details [Abstract]	'
Balance Sheet Details	'
	Balance Sheet Details
	Goodwill
	Changes in the carrying amount of Goodwill during fiscal years 2013 and 2012 are summarized as follows (in thousands):
	Balance, September 30, 2011	$	234,691
	Acquisition of Traffix Systems	113,210
	Other	338
	Balance, September 30, 2012	348,239
	Acquisition of LineRate Systems	99,560
	Acquisition of Versafe	75,937
	Other	(9		)
	Balance, September 30, 2013	$	523,727
	Other Assets
	Other assets consist of the following (in thousands):
		September 30,
		2013			2012
	Acquired and developed technology and software development costs	$	59,453		$	18,129
	Deposits and other	15,251			10,688
	Restricted cash	860			179
		$	75,564		$	28,996
	Amortization expense related to other assets was approximately $4.3 million, $6.4 million, and $4.3 million for the fiscal years ended September 30, 2013, 2012 and 2011, respectively.
	Intangible assets are included in other assets on the balance sheet and consist of the following (in thousands):
		2013								2012
		Gross			Accumulated			Net Carrying		Gross		Accumulated			Net Carrying
		Carrying			Amortization			Amount		Carrying		Amortization			Amount
		Amount								Amount
	Acquired and developed technology and software development costs	$	99,463		$	(40,010	)	$	59,453	$	54,240	$	(36,111	)	$	18,129
	Customer relationships	8,399			(3,123		)	5,276		5,379		(2,855		)	2,524
	Patents and trademarks	3,044			(2,525		)	519		3,044		(2,464		)	580
	Trade names	1,173			(250		)	923		263		(218		)	45
	Non-compete covenants	2,160			(200		)	1,960		200		(200		)	—
		$	114,239		$	(46,108	)	$	68,131	$	63,126	$	(41,848	)	$	21,278
	Estimated amortization expense for intangible assets for the five succeeding fiscal years is as follows (in thousands):
	2014	$	8,385
	2015	8,372
	2016	8,372
	2017	5,954
	2018	4,554
		$	35,637
	Accrued Liabilities
	Accrued liabilities consist of the following (in thousands):
		September 30,
		2013			2012
	Payroll and benefits	$	73,461		$	61,720
	Sales and marketing	3,746			4,407
	Income tax accruals	4,196			8,621
	Other	11,205			11,661
		$	92,608		$	86,409

Income_Taxes

Income Taxes	12 Months Ended
	Sep. 30, 2013
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,
		2013			2012			2011
	United States	$	431,833		$	421,346		$	342,741
	International	6,259			10,868			18,010
		$	438,092		$	432,214		$	360,751
	The provision for income taxes (benefit) consists of the following (in thousands):
		Years Ended September 30,
		2013			2012			2011
	Current
	U.S. federal	$	138,372		$	147,774		$	103,620
	State	14,322			10,733			7,397
	Foreign	6,633			4,218			5,743
	Total	159,327			162,725			116,760
	Deferred
	U.S. federal	1,310			(7,320		)	3,070
	State	(203		)	187			(144		)
	Foreign	344			1,436			(332		)
	Total	1,451			(5,697		)	2,594
		$	160,778		$	157,028		$	119,354
	The effective tax rate differs from the U.S. federal statutory rate as follows (in thousands):
		Years Ended September 30,
		2013			2012			2011
	Income tax provision at statutory rate	$	153,332		$	151,275		$	126,263
	State taxes, net of federal benefit	10,944			8,733			5,365
	Foreign operations	4,786			1,850			(971		)
	Research and development and other credits	(10,649		)	(3,537		)	(11,860		)
	Domestic manufacturing deduction	(14,047		)	(12,539		)	(9,351		)
	Stock-based and other compensation	15,286			10,501			9,388
	Other	1,126			745			520
		$	160,778		$	157,028		$	119,354
	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,
		2013			2012
	Deferred tax assets
	Net operating loss carry-forwards	$	10,072		$	1,366
	Allowance for doubtful accounts	1,112			1,106
	Accrued compensation and benefits	7,272			6,371
	Inventories and related reserves	1,120			1,223
	Stock-based compensation	5,933			11,713
	Deferred revenue	26,277			23,372
	Other accruals and reserves	10,131			9,594
	Tax credit carry-forwards	2,122			793
		64,039			55,538
	Valuation allowance	(5,390		)	(208		)
		58,649			55,330
	Deferred tax liabilities
	Purchased intangibles and other	(21,567		)	(6,329		)
	Depreciation	(3,697		)	(3,161		)
		(25,264		)	(9,490		)
	Net deferred tax assets	$	33,385		$	45,840
	At September 30, 2013, the Company had foreign net operating loss carry-forwards of approximately $43.3 million that can be carried forward indefinitely. In addition, there are $13.0 million of federal net operating loss carryforwards, the annual utilization of which is limited under Internal Revenue Code Section 382, and will expire in fiscal years 2031 and 2032. Management believes that it is more likely than not that the benefit from certain foreign net operating loss carry-forwards will not be realized. In recognition of this risk, the Company has provided a valuation allowance on the deferred tax assets relating to these foreign net operating loss carryforwards.
	United States income and foreign withholding taxes have not been provided on approximately $22.9 million of undistributed earnings from the Company’s international subsidiaries. The Company has not recognized a deferred tax liability for the undistributed earnings of its foreign subsidiaries because the Company currently does not expect to remit those earnings in the foreseeable future. Determination of the amount of unrecognized deferred tax liability related to undistributed earnings of foreign subsidiaries is not practicable because such liability, if any, is dependent on circumstances existing if and when remittance occurs.
	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 2013, 2012 and 2011:
		2013			2012			2011
	Balance, beginning of period	$	5,452		$	5,952		$	6,568
	Gross increases (decreases) related to prior period tax positions	1,089			(201		)	1,198
	Gross increases related to current period tax positions	1,957			702			1,659
	Decreases relating to settlements with tax authorities	—			(3		)	(243		)
	Reductions due to lapses of statute of limitations	(1,196		)	(998		)	(3,230		)
	Balance, end of period	$	7,302		$	5,452		$	5,952
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, 2013, 2012 and 2011 the Company recorded approximately $244,000, $250,000 and $283,000, respectively, of interest expense related to uncertain tax positions. As of September 30, 2013 and 2012, the Company had a cumulative balance of accrued interest on unrecognized tax positions of $431,000 and $406,000, respectively.
All unrecognized tax benefits, 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 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, 2009. The Company is currently under audit by the IRS for fiscal years 2011 and 2012, and various states for fiscal years 2009 through 2012. 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 2012 for the United Kingdom, 2007 for Japan, 2008 for Singapore, and 2009 for Australia. Within the next four fiscal quarters, the statute of limitations will begin to close on the fiscal years 2009 and 2010 state income tax returns, and the fiscal year 2010 federal income tax return.

StockBased_Compensation

Stock-Based Compensation	12 Months Ended
	Sep. 30, 2013
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 10 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.
	1998 Equity Incentive Plan. In November 1998, the Company adopted the 1998 Equity Incentive Plan, or the 1998 Plan, which provided for discretionary grants of non-qualified and incentive stock options, stock purchase awards and stock bonuses for employees and other service providers. The 1998 Plan expired on November 11, 2008 and no shares remain available for awards under the 1998 Plan. Upon certain changes in control of the Company, all outstanding and unvested options or stock awards under the 1998 Plan will vest at the rate of 50%, unless assumed or substituted by the acquiring entity. During the fiscal years 2013 and 2012, the Company issued no stock options, stock purchase awards or stock bonuses under this plan. As of September 30, 2013, there were options to purchase 52,753 shares outstanding under the 1998 Plan.
	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 6,000,000 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, 2013 there were 1,014,179 shares available for awards under the Employee Stock Purchase Plan.
	2000 Equity Incentive Plan. In July 2000, the Company adopted the 2000 Employee Equity Incentive Plan, or the 2000 Plan, which provided for discretionary grants of non-qualified stock options, stock purchase awards and stock bonuses for non-executive employees and other service providers. A total of 7,000,000 shares of common stock were reserved for issuance under the 2000 Plan. Upon certain changes in control of the Company, all outstanding and unvested options or stock awards under the 2000 Plan will vest at the rate of 50%, unless assumed or substituted by the acquiring entity. As of September 30, 2013, there were options to purchase 40,958 shares outstanding and no shares available for awards under the 2000 Plan. The Company terminated the 2000 Plan effective November 1, 2008 and no additional shares may be issued from the 2000 Plan.
	Acquisition Related Incentive Plans. In July 2003, the Company adopted the uRoam Acquisition Equity Incentive Plan, or the uRoam Plan, in connection with the hiring of the former employees of uRoam, Inc. A total of 500,000 shares of common stock were reserved for issuance under the uRoam Plan. The plan provided for discretionary grants of non-qualified and incentive stock options, stock purchase awards and stock bonuses. The Company has not granted any stock purchase awards or stock bonuses under this plan. As of September 30, 2013 there were options to purchase 1,650 shares outstanding and no shares available for additional awards under the uRoam Plan.
	In July 2004, the Company adopted the MagniFire Acquisition Equity Incentive Plan, or the MagniFire Plan, in connection with the hiring of the former employees of MagniFire Websystems, Inc. A total of 830,000 shares of common stock were reserved for issuance under the MagniFire Plan. The plan provided for discretionary grants of non-qualified and incentive stock options, stock purchase awards and stock bonuses. The Company has not granted any stock purchase awards or stock bonuses under this plan. As of September 30, 2013 there were options to purchase 2,690 shares outstanding and no shares available for additional awards under the MagniFire Plan.
	In connection with the Company’s acquisition of Acopia in the fourth quarter of fiscal year 2007, the Company assumed the Acopia 2001 Stock Incentive Plan, or the Acopia Plan. Unvested options to acquire Acopia’s common stock were converted into options to acquire the Company’s common stock in connection with the acquisition. A total of 2,230,703 shares of common stock were reserved for issuance under the Acopia Plan. The plan provided for discretionary grants of non-qualified and incentive stock options, restricted stock awards and other stock-based awards to persons who were employees, officers, directors, consultants or advisors to Acopia on or prior to September 12, 2007. During the fiscal year 2013, the Company issued no stock options or restricted stock units under the Acopia Plan. As of September 30, 2013, there were options to purchase 12,509 shares outstanding and no shares available for awards under the Acopia Plan. The Company terminated the Acopia Plan effective November 1, 2008 and no additional shares may be issued from the Acopia Plan.
	In February 2012, the Company adopted the Traffix Acquisition Equity Incentive Plan, or the Traffix Acquisition Plan. The Traffix Acquisition Plan provided for discretionary grants of non-statutory stock options and stock units for employees, directors and consultants of Traffix Communication Systems Ltd. to whom the Company offered employment in connection with the Company’s acquisition of Traffix. A total of 75,000 shares of common stock were reserved for issuance under the Traffix Acquisition Plan. Upon certain changes in control of the Company, the surviving entity will either assume or substitute all outstanding stock awards under the Traffix Acquisition Plan or the vesting of 50% of the stock awards shall be accelerated. During the fiscal year 2013, the Company issued no stock options or restricted stock units under the Traffix Acquisition Plan. As of September 30, 2013, there were no options outstanding, 33,693 restricted stock units outstanding and no shares available for awards under the Traffix Acquisition Plan.
	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 2013, the Company issued no stock options or restricted stock units under the Traffix Plan. As of September 30, 2013, there were options to purchase 56,758 shares outstanding and no shares available for additional awards under the Traffix Plan.
	In February 2013, the Company adopted the LineRate Acquisition Equity Incentive Plan, or the LineRate Acquisition Plan. The LineRate Acquisition Plan provided for discretionary grants of non-statutory stock options and stock units for employees, directors and consultants of LineRate Systems to whom the Company offered employment in connection with the Company’s acquisition of LineRate Systems. A total of 100,000 shares of common stock were reserved for issuance under the LineRate Acquisition Plan. Upon certain changes in control of the Company, the surviving entity will either assume or substitute all outstanding stock awards under the LineRate Acquisition Plan or the vesting of 50% of the stock awards shall be accelerated. During the fiscal year 2013, the Company issued no stock options and 100,000 restricted stock units under the LineRate Acquisition Plan. As of September 30, 2013, there were no options outstanding, 100,000 restricted stock units outstanding and no shares available for awards under the LineRate Acquisition Plan.
	In connection with the Company’s acquisition of LineRate Systems in the second quarter of fiscal year 2013, the Company assumed the LineRate Systems, Inc. Third Amended and Restated 2009 Equity Incentive Plan, or the LineRate Plan. Unvested options to acquire LineRate Systems' common stock were converted into options to acquire the Company’s common stock in connection with the acquisition. A total of 201,478 shares of common stock were reserved for issuance under the LineRate Plan. The plan provided for grants of stock options to persons who were employees, officers, directors, consultants or advisors to LineRate Systems on or prior to February 11, 2013. During the fiscal year 2013, the Company issued 52,397 stock options as part of such conversion under the LineRate Plan. As of September 30, 2013, there were options to purchase 42,901 shares outstanding and 3,574 shares available for additional awards under the LineRate Plan.
	In September 2013, the Company adopted the Versafe Acquisition Equity Incentive Plan, or the Versafe Acquisition Plan. The Versafe Acquisition Plan provided for discretionary grants of non-statutory stock options and stock units for employees, directors and consultants of Versafe Ltd. to whom the Company offered employment in connection with the Company’s acquisition of Versafe. A total of 60,000 shares of common stock were reserved for issuance under the Versafe Acquisition Plan. Upon certain changes in control of the Company, the surviving entity will either assume or substitute all outstanding stock awards under the Versafe Acquisition Plan or the vesting of 50% of the stock awards shall be accelerated. During the fiscal year 2013, the Company issued no stock options and no restricted stock units under the Versafe Acquisition Plan. As of September 30, 2013, there were no options outstanding, no restricted stock units outstanding and 60,000 shares available for awards under the Versafe Acquisition Plan.
	2005 Equity Incentive Plan. In December 2004, the Company adopted the 2005 Equity Incentive Plan, or the 2005 Plan, which provides for discretionary grants of non-statutory stock options and stock units for employees, including officers, and other service providers. A total of 12,400,000 shares of common stock have been reserved for issuance under the 2005 Plan. Upon certain changes in control of the Company, all outstanding and unvested options or stock awards under the 2005 Plan will vest at the rate of 50%, unless assumed or substituted by the acquiring entity. During the fiscal year 2013, the Company issued no stock options and 456,837 restricted stock units under the 2005 Plan. As of September 30, 2013, there were no options outstanding, 926,035 restricted stock units outstanding and 2,135,162 shares available for new awards under the 2005 Plan.
	A majority of the restricted stock units the Company grants to its employees vest quarterly over a two-year period. The restricted stock units under all plans were granted during fiscal years 2013, 2012 and 2011 with a per-share weighted average fair value of $86.69, $99.63 and $94.99, respectively. The fair value of restricted stock vested during fiscal years 2013, 2012 and 2011 was $97.5 million, $93.8 million and $145.0 million, respectively.
	A summary of restricted stock unit activity under the 2005 Plan is as follows:
			Outstanding		Weighted
			Stock Units		Average
					Grant Date
					Fair Value
	Balance, September 30, 2012		1,717,444		$	95.43
	Units granted		456,837		89.38
	Units vested		(1,078,607	)	89.31
	Units cancelled		(169,639	)	94.16
	Balance, September 30, 2013		926,035		$	95.47
	A summary of stock option activity under all of the Company’s plans is as follows:
			Options Outstanding
			Number of		Weighted
			Shares		Average
					Exercise Price
					per Share
	Balance, September 30, 2012		284,474		$	11.73
	Options granted		52,397		1.32
	Options exercised		(125,701	)	10.67
	Options cancelled		(951	)	3.95
	Balance, September 30, 2013		210,219		$	9.8
	All stock options granted in fiscal year 2013 were assumed as part of the acquisition of LineRate Systems in the second fiscal quarter. All stock options granted in fiscal year 2012 were assumed as part of the acquisition of Traffix Systems in the second fiscal quarter. No stock options were granted in fiscal years 2011.
	The total intrinsic value of options exercised during fiscal 2013, 2012 and 2011 was $9.8 million, $13.2 million and $15.2 million, respectively.
			Number of		Weighted		Weighted		Aggregate
			Shares		Average		Average		Intrinsic
					Remaining		Exercise		Value(1)
					Contractual		Price
					Life (in Years)		per Share
									(In thousands)
	Stock options outstanding		210,219		4.37		$	9.8	$	15,967
	Exercisable		140,054		2.46		$	13.48	$	10,123
	Vested and expected to vest		204,688		4.27		$	10.01	$	15,506
	-1	Aggregate intrinsic value represents the difference between the fair value of the Company’s common stock underlying these options at September 30, 2013 and the related exercise prices.
	As of September 30, 2013, equity based awards (including stock options and restricted stock units) are available for future issuance as follows:
			Awards
			Available for
			Grant
	Balance, September 30, 2012		2,422,360
	Granted		(609,234	)
	Cancelled		172,324
	Additional shares reserved (terminated), net		213,286
	Balance, September 30, 2013		2,198,736

Commitments_And_Contingencies

Commitments And Contingencies	12 Months Ended
	Sep. 30, 2013
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 three building corporate headquarters in Seattle, Washington. In April 2010, the lease for all three buildings was amended and now the lease will expire in 2022 with an option for renewal. 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 three buildings that serve as the Company’s corporate headquarters. The lease expires in 2018. The Company is currently subleasing all floors of this building to two subtenants. Both subleases will expire in 2018.
	Future minimum operating lease payments, net of sublease income, are as follows (in thousands):
		Gross Lease		Sublease		Net Lease
		Payments		Income		Payments
	2014	23,714		4,013		19,701
	2015	19,741		4,028		15,713
	2016	17,192		3,993		13,199
	2017	17,022		4,102		12,920
	2018	15,293		2,770		12,523
	Thereafter	42,279		—		42,279
		$	135,241	$	18,906	$	116,335
	Rent expense under non-cancelable operating leases amounted to approximately $26.5 million, $21.6 million, and $19.0 million for the fiscal years ended September 30, 2013, 2012, and 2011, respectively. In August 2013, the Company incurred a charge of $2.4 million related to the consolidation of certain subleases at its corporate headquarters.
	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, 2013, the Company’s purchase obligations were $16.4 million.
	Litigation
	Management is not aware of any pending legal proceedings that, individually or in the aggregate, are reasonably possible to have a material adverse effect on the Company’s business, operating results, or financial condition. The Company is subject to a variety of other claims and suits that arise from time to time in the ordinary course of business. Although management currently believes that resolving claims against the Company, individually or in aggregate, will not have a material adverse impact on its financial statements, these matters are subject to inherent uncertainties and management’s view of these matters may change in the future. Such claims, even if not meritorious, could result in the expenditure of significant financial and managerial resources.

Employee_Benefit_Plans

Employee Benefit Plans	12 Months Ended
	Sep. 30, 2013
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, 2013, 2012, and 2011 were approximately $6.4 million, $5.7 million and $4.7 million, respectively. Contributions made by the Company vest over four years.

Geographic_Sales_And_Significa

Geographic Sales And Significant Customers	12 Months Ended
	Sep. 30, 2013
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. 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 Company’s assets are primarily located in the United States. Therefore, geographic information is presented only for net revenue.
	The following presents revenues by geographic region (in thousands):
		Years Ended September 30,
		2013		2012		2011
	Americas:
	United States	$	777,516	$	729,238	$	627,806
	Other	74,391		64,144		49,062
	Total Americas	851,907		793,382		676,868
	EMEA	327,109		294,191		240,453
	Japan	83,051		90,521		74,824
	Asia Pacific	219,247		199,153		159,689
		$	1,481,314	$	1,377,247	$	1,151,834
	One worldwide distributor of the Company’s products accounted for 16.6%, 17.1%, and 18.1% of total net revenues in fiscal years 2013, 2012, and 2011, respectively. Another worldwide distributor of the Company’s products accounted for 15.7%, 13.8% and 10.7% of total net revenues in fiscal years 2013, 2012 and 2011, respectively. Another worldwide distributor of the Company’s products accounted for 11.8% of total net revenue in fiscal year 2013. One worldwide distributor accounted for 18.6% of the Company’s accounts receivable as of September 30, 2013. Two worldwide distributors accounted for 13.4% and 12.0% of the Company’s accounts receivable as of September 30, 2012. No other distributors accounted for more than 10% of total net revenue or receivables.

Quarterly_Results_Of_Operation

Quarterly Results Of Operations	12 Months Ended
	Sep. 30, 2013
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, 2013. 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, 2013		30-Jun-13		31-Mar-13		Dec. 31, 2012		Sept. 30, 2012		30-Jun-12		31-Mar-12		Dec. 31, 2011
		(Unaudited and in thousands, except per share data)
	Net revenues
	Products	$	212,291	$	196,746	$	185,107	$	204,712	$	209,718	$	207,118	$	205,165	$	196,554
	Services	183,038		173,556		165,125		160,739		152,841		145,516		134,457		125,878
	Total	395,329		370,302		350,232		365,451		362,559		352,634		339,622		322,432
	Cost of net revenues
	Products	35,151		32,350		29,773		31,792		35,752		34,482		33,668		33,200
	Services	31,792		32,567		30,529		29,093		26,929		25,805		23,926		22,406
	Total	66,943		64,917		60,302		60,885		62,681		60,287		57,594		55,606
	Gross profit	328,386		305,385		289,930		304,566		299,878		292,347		282,028		266,826
	Operating expenses
	Sales and marketing	119,836		121,906		119,031		122,268		116,298		112,064		110,995		106,238
	Research and development	54,464		54,075		52,534		48,541		47,731		46,985		43,568		39,122
	General and administrative	26,512		25,327		25,889		24,673		24,015		23,298		22,785		21,677
	Loss on facility sublease	2,393		—		—		—		—		—		—		—
	Total operating expenses	203,205		201,308		197,454		195,482		188,044		182,347		177,348		167,037
	Income from operations	125,181		104,077		92,476		109,084		111,834		110,000		104,680		99,789
	Other income, net	732		2,874		2,118		1,550		909		1,713		1,428		1,861
	Income before income taxes	125,913		106,951		94,594		110,634		112,743		111,713		106,108		101,650
	Provision for income taxes	49,682		38,773		31,182		41,141		45,026		39,377		37,467		35,158
	Net income	$	76,231	$	68,178	$	63,412	$	69,493	$	67,717	$	72,336	$	68,641	$	66,492
	Net income per share — basic	$	0.97	$	0.87	$	0.81	$	0.88	$	0.86	$	0.91	$	0.87	$	0.84
	Weighted average shares — basic	78,353		78,516		78,601		78,789		78,980		79,135		79,156		79,272
	Net income per share — diluted	$	0.97	$	0.86	$	0.8	$	0.88	$	0.85	$	0.91	$	0.86	$	0.83
	Weighted average shares — diluted	78,674		78,864		79,114		79,278		79,425		79,655		79,775		79,822

Summary_Of_Significant_Account1

Summary Of Significant Accounting Policies (Policy)	12 Months Ended
	Sep. 30, 2013
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.
Reclassifications	'
	Reclassifications
	In Note 6, Income Taxes, certain prior year amounts have been reclassified to conform to the current year presentation. There was no change to the total amount of income tax expense or net deferred tax asset as a result of the reclassifications.
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 four 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 and United States government and agency 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, 2013, Ingram Micro, Inc. accounted for 18.6% of the Company’s accounts receivable. At September 30, 2012, Avnet Technology Solutions and Ingram Micro, Inc. accounted for 13.4% and 12.0% of the Company’s accounts receivable, respectively.
	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 or market (as determined by the first-in, first-out method).
Property And Equipment	'
	Property and Equipment
	Property and equipment is stated at cost. 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 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 the acquisition of Versafe Ltd. in September 2013, LineRate Systems, Inc. in February 2013, Traffix Systems in fiscal year 2012, Acopia Networks, Inc. in fiscal year 2007, Swan Labs, Inc. in fiscal year 2006, MagniFire Websystems, Inc. in fiscal year 2004 and uRoam, Inc. in fiscal year 2003. For its annual goodwill impairment test, the Company operates under one reporting unit and the fair value of its reporting unit is 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 first performs a qualitative assessment to determine whether further impairment testing is necessary. 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.
	Examples of events and circumstances that might indicate that a 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 an expectation that a reporting unit will be sold or a sustained decrease in the stock price on either an absolute basis or relative to peers.
	If it is determined, as a result of the qualitative assessment, that it is more-likely-than-not that the fair value of the Company’s reporting unit is less than its carrying amount, the provisions of authoritative guidance require that the Company perform a two-step impairment test on goodwill. The first step of the test identifies whether potential impairment may have occurred, while the second step of the test measures the amount of the impairment, if any. Impairment is recognized when the carrying amount of goodwill exceeds its fair value. In March 2013, the Company completed a qualitative assessment of potential impairment indicators and concluded that it was more-likely-than-not that the fair value of its reporting unit exceeded its carrying amount. The Company also considered potential impairment indicators at September 30, 2013 and noted no indicators of impairment.
Other Assets	'
	Other Assets
	Other assets primarily consist of acquired and developed technology, software development costs and customer relationships.
	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. IPR&D was recorded in connection with the acquisition of LineRate Systems, Inc. in February 2013.
	Acquired and developed technology is recorded at cost and amortized over its estimated useful life of five years. The estimated useful life of these assets is assessed and evaluated for reasonableness periodically. Acquired technology of $15.4 million in fiscal year 2013 and $14.9 million in fiscal 2012 was recorded in connection with the acquisitions of Versafe and Traffix Systems, respectively. Amortization expense related to acquired technology, which is charged to cost of product revenues, totaled $3.8 million, $5.3 million and $3.1 million during the fiscal years 2013, 2012 and 2011, respectively.
	Software development costs are charged to research and development expense in the period incurred until technological feasibility is established. Thereafter, until the product is released for sale, software development costs are capitalized and reported at the lower of unamortized cost or net realizable value of each product. 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 did not capitalize any software development costs in fiscal years 2013, 2012 and 2011. Amortization expense related to capitalized software development was immaterial for fiscal years 2013, 2012, and 2011.
	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 recovery 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 2013, 2012 and 2011.
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 year ended September 30, 2013.
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. In certain regions where the Company does not have the ability to reasonably estimate returns, the Company defers revenue on sales to its distributors until information is received from the channel partner indicating that the product has been sold to the end-user customer. 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. The Company offers extended payment terms to certain customers, in which case, revenue is recognized when payments are due.
	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 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 its 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, 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, 2013, 2012 and 2011 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 statements of income as incurred.
Advertising	'
	Advertising
	Advertising costs are expensed as incurred. The Company incurred $2.8 million, $1.8 million and $2.2 million in advertising costs during the fiscal years 2013, 2012 and 2011, 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 Ltd. in the United Kingdom and F5 Networks (Israel) Ltd., Traffix Communication Systems Ltd. and Versafe Ltd. in 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. The net effect of foreign currency gains and losses was not significant during the fiscal years ended September 30, 2013, 2012 and 2011.
Segments	'
	Segments
	Management has determined that the Company was organized as, and operated in, one reportable operating segment for fiscal year 2013 and prior years: the development, marketing and sale of application delivery networking products 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 $104.2 million, $95.3 million and $89.7 million of stock-based compensation expense for the fiscal years ended September 30, 2013, 2012 and 2011, respectively. As of September 30, 2013, there was $82.5 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 29, 2013, the Company’s Compensation Committee approved 1,467,871 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. All stock options granted in fiscal years 2013 and 2012 were assumed as part of the acquisitions of LineRate Systems and Traffix Systems, respectively, in the second fiscal quarter of each year. No stock options were granted in fiscal year 2011. 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
			Years Ended September 30,
			2013		2012		2011
	Risk-free interest rate		0.06	%	0.14	%	0.1	%
	Expected dividend		—		—		—
	Expected term		0.5 years		0.5 years		0.5 years
	Expected volatility		42.92	%	45.2	%	53.87	%
	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 estimated forfeiture rate for grants awarded to the Company’s executive officers and Board of Directors was approximately 7% and the estimated forfeiture rate for grants awarded to all other employees was approximately 8% in fiscal 2013. If the actual number of forfeitures differs from those estimated by management, additional adjustments to compensation expense may be required in future periods.
	In November 2012, the Company granted 290,415 RSUs to certain current executive officers as part of the annual equity awards program. Fifty percent of the aggregate number of RSUs vest in equal quarterly increments over four years, until such portion of the grant is fully vested on November 1, 2016. One-eighth of the RSU grant, or a portion thereof, was subject to the Company achieving specified quarterly revenue and EBITDA goals during fiscal year 2013. In each case, 50% of the quarterly performance stock grant is based on achieving at least 80% of the quarterly revenue goal and the other 50% is based on achieving at least 80% of the quarterly EBITDA goal. The quarterly performance stock grant is paid linearly above 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 100% over-achievement threshold. The remaining 37.5% of this annual equity awards RSU grant shall be subject to quarterly performance based vesting for fiscal years 2014, 2015 and 2016 (12.5% in each period). The Compensation Committee of the Board of Directors will set applicable performance targets and vesting formulas for each of these periods.
	In November 2011, as part of the annual review of executive compensation by the Compensation Committee of the Board of Directors and a change in the grant date for the Company’s annual equity awards program for the executive officers from August 1 to November 1, the Company granted 82,968 RSUs to certain current executive officers. Fifty percent of the aggregate number of RSUs vest in equal quarterly increments over three years, until such portion of the grant is fully vested on November 1, 2014. One-sixth of the RSU grant, or a portion thereof, was subject to the Company achieving specified quarterly revenue and EBITDA goals during fiscal year 2012. The remaining 33.33% of this annual equity awards RSU grant shall be subject to quarterly performance based vesting for fiscal years 2013 and 2014 (16.66% in each period). The Compensation Committee of the Board of Directors will set applicable performance targets and vesting formulas for each of these periods.
	In August 2011, the Company granted 170,390 RSUs to certain current executive officers as part of the annual equity awards program. Fifty percent of the aggregate number of RSUs granted as part of the annual equity awards program vest in equal quarterly increments over three years, until such portion of the grant is fully vested on August 1, 2014. One-sixth of the annual equity awards RSU grant, or a portion thereof, was subject to the Company achieving specified quarterly revenue and EBITDA goals during the period beginning in the fourth quarter of fiscal year 2011 through the third quarter of fiscal year 2012. The remaining 33.33% of this annual equity awards RSU grant shall be subject to performance based vesting for each of the four quarter periods beginning with the fourth quarters of fiscal years 2012 and 2013 (16.66% in each period). The Compensation Committee of the Board of Directors will set applicable performance targets and vesting formulas for each of these periods.
	In August 2010, the Company granted 181,334 and 83,000 RSUs to certain current executive officers as part of the annual equity and retention awards programs, respectively. Fifty percent of the aggregate number of RSUs granted as part of the annual equity awards program vested in equal quarterly increments over three years, until such portion of the grant was fully vested on August 1, 2013.
	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 April 24, 2013, the Company announced that its Board of Directors authorized an additional $200 million for its common stock share repurchase program. This new authorization is incremental to the existing $600 million program, initially approved in October 2010 and expanded in August 2011 and October 2011. 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. As of November 15, 2013, the Company had repurchased and retired 12,289,015 shares at an average price of $72.18 per share and the Company had $112.5 million remaining to purchase shares as part of its repurchase programs.
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 awards and restricted stock units do not have nonforfeitable rights to dividends or dividend equivalents.
Recent Accounting Pronouncements	'
	Recent Accounting Pronouncements
	In February 2013, the FASB issued ASU 2013-2, Comprehensive Income (Topic 220): Reporting of Amounts Reclassified out of Accumulated Other Comprehensive Income (ASU 2013-2), to improve the reporting of reclassifications out of accumulated other comprehensive income. ASU 2013-2 requires presentation, either on the face of the financial statements or in the notes, of amounts reclassified out of accumulated other comprehensive income by component and by net income line item. ASU 2013-2 is effective prospectively for fiscal years, and interim periods within those years, beginning after December 15, 2012. The Company will adopt ASU 2013-2 in the first quarter of fiscal 2014 and does not expect the adoption of this standard to have an impact on its consolidated financial statements.

Summary_Of_Significant_Account2

Summary Of Significant Accounting Policies (Tables)	12 Months Ended
	Sep. 30, 2013
Accounting Policies [Abstract]	'
Schedule Of Inventories	'
	Inventories consist of the following (in thousands):
		September 30,
		2013				2012
	Finished goods	$	13,509			$	13,565
	Raw materials	5,517				3,845
		$	19,026			$	17,410
Schedule Of Property And Equipment	'
	Property and equipment consist of the following (in thousands):
		September 30,
		2013				2012
	Computer equipment	$	93,326			$	95,987
	Office furniture and equipment	13,391				12,335
	Leasehold improvements	54,972				43,957
		161,689				152,279
	Accumulated depreciation and amortization	(98,167		)		(92,675		)
		$	63,522			$	59,604
Schedule Of Assumptions In Determining The Fair Value Of Shares Issued Under The Employee Stock Purchase Plan	'
		Employee Stock Purchase Plan
		Years Ended September 30,
		2013			2012			2011
	Risk-free interest rate	0.06	%		0.14	%		0.1	%
	Expected dividend	—			—			—
	Expected term	0.5 years			0.5 years			0.5 years
	Expected volatility	42.92	%		45.2	%		53.87	%
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,
		2013				2012				2011
	Numerator
	Net income	$	277,314			$	275,186			$	241,397
	Denominator
	Weighted average shares outstanding — basic	78,565				79,135				80,658
	Dilutive effect of common shares from stock options and restricted stock units	571				645				824
	Weighted average shares outstanding — diluted	79,136				79,780				81,482
	Basic net income per share	$	3.53			$	3.48			$	2.99
	Diluted net income per share	$	3.5			$	3.45			$	2.96

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Sep. 30, 2013
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, 2013, were as follows (in thousands):
		Fair Value Measurements at Reporting Date Using								Fair Value at
										September 30,
		Quoted Prices in			Significant			Significant		2013
		Active Markets for			Other Observable			Unobservable
		Identical Securities			Inputs			Inputs
		(Level  1)			(Level 2)			(Level 3)
	Cash equivalents	$	13,145		$	—		$	—	$	13,145
	Short-term investments
	Available-for-sale securities — corporate bonds and notes	—			125,212			—		125,212
	Available-for-sale securities — municipal bonds and notes	—			72,164			—		72,164
	Available-for-sale securities — U.S. government securities	—			5,000			—		5,000
	Available-for-sale securities — U.S. government agency securities	—			150,074			—		150,074
	Long-term investments
	Available-for-sale securities — corporate bonds and notes	—			260,318			—		260,318
	Available-for-sale securities — municipal bonds and notes	—			24,371			—		24,371
	Available-for-sale securities — U.S. government securities	—			14,798			—		14,798
	Available-for-sale securities — U.S. government agency securities	—			426,458			—		426,458
	Available-for-sale securities — auction rate securities	—			—			3,036		3,036
	Total	$	13,145		$	1,078,395		$	3,036	$	1,094,576
	The Company’s financial assets measured at fair value on a recurring basis subject to the disclosure requirements at September 30, 2012, were as follows (in thousands):
		Fair Value Measurements at Reporting Date Using								Fair Value at
										September 30,
		Quoted Prices in			Significant			Significant		2012
		Active Markets for			Other Observable			Unobservable
		Identical Securities			Inputs			Inputs
		(Level 1)			(Level 2)			(Level 3)
	Cash equivalents	$	35,658		$	—		$	—	$	35,658
	Short-term investments
	Available-for-sale securities — certificates of deposit	—			3,533			—		3,533
	Available-for-sale securities — corporate bonds and notes	—			193,990			—		193,990
	Available-for-sale securities — municipal bonds and notes	—			63,422					63,422
	Available-for-sale securities — U.S. government agency securities	—			60,025			—		60,025
	Long-term investments
	Available-for-sale securities — corporate bonds and notes	—			229,441			—		229,441
	Available-for-sale securities — municipal bonds and notes	—			30,307			—		30,307
	Available-for-sale securities — U.S. government securities	—			4,995			—		4,995
	Available-for-sale securities — U.S. government agency securities	—			393,310			—		393,310
	Available-for-sale securities — auction rate securities	—			—			4,750		4,750
	Total	$	35,658		$	979,023		$	4,750	$	1,019,431
Schedule Of Reconciliation Of Items Measured At Fair Value On A Recurring Basis That Used Significant Unobservable Inputs (Level 3)	'
	The following table provides a reconciliation between the beginning and ending balances of items measured at fair value on a recurring basis in the tables above that used significant unobservable inputs (Level 3) (in thousands):
		2013			2012
	Balance, beginning of period	$	4,750		$	13,010
	Total (losses) gains realized or unrealized:
	Included in other comprehensive income	(14		)	1,740
	Settlements	(1,700		)	(10,000		)
	Balance, end of period	$	3,036		$	4,750
	Unrealized (losses) gains attributable to assets still held as of the end of the period	(14		)	112

ShortTerm_And_LongTerm_Investm1

Short-Term And Long-Term Investments (Tables)	12 Months Ended
	Sep. 30, 2013
Schedule of Investments [Line Items]	'
Schedule Of Amortized Cost And Fair Value Of Fixed Maturities By Contractual Years-To-Maturity	'
	The amortized cost and fair value of fixed maturities at September 30, 2013, by contractual years-to-maturity, are presented below (in thousands):
	September 30, 2013	Cost or		Fair Value
		Amortized
		Cost
	One year or less	$	352,193	$	352,450
	Over one year	729,348		728,981
		$	1,081,541	$	1,081,431
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, 2013 (in thousands):
		Less Than 12 Months					12 Months or Greater						Total
	September 30, 2013	Fair Value		Gross			Fair			Gross			Fair Value		Gross
				Unrealized			Value			Unrealized					Unrealized
				Losses						Losses					Losses
	Corporate bonds and notes	$	171,144	$	(397	)	$	3,181		$	(1	)	$	174,325	$	(398	)
	Municipal bonds and notes	20,080		(15		)	—			—			20,080		(15		)
	Auction rate securities	—		—			3,036			(264		)	3,036		(264		)
	U.S. government agency securities	317,773		(462		)	—			—			317,773		(462		)
	Total	$	508,997	$	(874	)	$	6,217		$	(265	)	$	515,214	$	(1,139	)
Short-Term Investments [Member]	'
Schedule of Investments [Line Items]	'
Schedule Of Short-Term And Long-Term Investments	'
	Short-term investments consist of the following (in thousands):
	September 30, 2013	Cost or		Gross			Gross			Fair Value
		Amortized		Unrealized			Unrealized
		Cost		Gains			Losses
	Corporate bonds and notes	$	125,010	$	210		$	(8	)	$	125,212
	Municipal bonds and notes	72,116		58			(10		)	72,164
	U.S. government securities	4,998		2			—			5,000
	U.S. government agency securities	150,069		15			(10		)	150,074
		$	352,193	$	285		$	(28	)	$	352,450
	September 30, 2012	Cost or		Gross			Gross			Fair Value
		Amortized		Unrealized			Unrealized
		Cost		Gains			Losses
	Certificates of deposit	$	3,528	$	5		$	—		$	3,533
	Corporate bonds and notes	193,548		482			(40		)	193,990
	Municipal bonds and notes	63,371		61			(10		)	63,422
	U.S. government agency securities	60,010		15			—			60,025
		$	320,457	$	563		$	(50	)	$	320,970
Long-Term Investments [Member]	'
Schedule of Investments [Line Items]	'
Schedule Of Short-Term And Long-Term Investments	'
	September 30, 2013	Cost or		Gross			Gross			Fair Value
		Amortized		Unrealized			Unrealized
		Cost		Gains			Losses
	Corporate bonds and notes	$	260,345	$	363		$	(390	)	$	260,318
	Municipal bonds and notes	24,332		44			(5		)	24,371
	Auction rate securities	3,300		—			(264		)	3,036
	U.S. government securities	14,755		43			—			14,798
	U.S. government agency securities	426,616		294			(452		)	426,458
		$	729,348	$	744		$	(1,111	)	$	728,981
	September 30, 2012	Cost or		Gross			Gross			Fair Value
		Amortized		Unrealized			Unrealized
		Cost		Gains			Losses
	Corporate bonds and notes	$	228,438	$	1,063		$	(60	)	$	229,441
	Municipal bonds and notes	30,177		138			(8		)	30,307
	Auction rate securities	5,000		—			(250		)	4,750
	U.S. government securities	4,983		12			—			4,995
	U.S. government agency securities	392,959		389			(38		)	393,310
		$	661,557	$	1,602		$	(356	)	$	662,803

Business_Combinations_Tables

Business Combinations (Tables)	12 Months Ended
	Sep. 30, 2013
Line Rate Systems [Member]	'
Business Acquisition [Line Items]	'
Schedule Of Purchase Price Allocation	'
	The purchase price allocation is as follows (in thousands):
	Assets acquired
	Cash	$	82
	Current assets	556
	Property and equipment, net	415
	In-process research and development	29,853
	Goodwill	99,560
	Total assets acquired	$	130,466
	Liabilities assumed
	Accrued liabilities	$	(396	)
	Deferred tax liabilities, net	(4,763		)
	Total liabilities assumed	(5,159		)
	Net assets acquired	$	125,307
Versafe [Member]	'
Business Acquisition [Line Items]	'
Schedule Of Purchase Price Allocation	'
	The purchase price allocation is as follows (in thousands):
	Assets acquired
	Cash	$	4,020
	Current assets	1,309
	Property and equipment, net	41
	Developed technology, customer relationships and other intangibles	21,260
	Goodwill	75,937
	Total assets acquired	$	102,567
	Liabilities assumed
	Accrued liabilities	$	(4,877	)
	Deferred revenue	(611		)
	Deferred tax liabilities, net	(5,335		)
	Total liabilities assumed	(10,823		)
	Net assets acquired	$	91,744

Balance_Sheet_Details_Tables

Balance Sheet Details (Tables)	12 Months Ended
	Sep. 30, 2013
Balance Sheet Details [Abstract]	'
Schedule Of Goodwill	'
	Changes in the carrying amount of Goodwill during fiscal years 2013 and 2012 are summarized as follows (in thousands):
	Balance, September 30, 2011	$	234,691
	Acquisition of Traffix Systems	113,210
	Other	338
	Balance, September 30, 2012	348,239
	Acquisition of LineRate Systems	99,560
	Acquisition of Versafe	75,937
	Other	(9		)
	Balance, September 30, 2013	$	523,727
Schedule Of Other Assets	'
	Other assets consist of the following (in thousands):
		September 30,
		2013			2012
	Acquired and developed technology and software development costs	$	59,453		$	18,129
	Deposits and other	15,251			10,688
	Restricted cash	860			179
		$	75,564		$	28,996
Schedule Of Intangible Assets	'
	Intangible assets are included in other assets on the balance sheet and consist of the following (in thousands):
		2013								2012
		Gross			Accumulated			Net Carrying		Gross		Accumulated			Net Carrying
		Carrying			Amortization			Amount		Carrying		Amortization			Amount
		Amount								Amount
	Acquired and developed technology and software development costs	$	99,463		$	(40,010	)	$	59,453	$	54,240	$	(36,111	)	$	18,129
	Customer relationships	8,399			(3,123		)	5,276		5,379		(2,855		)	2,524
	Patents and trademarks	3,044			(2,525		)	519		3,044		(2,464		)	580
	Trade names	1,173			(250		)	923		263		(218		)	45
	Non-compete covenants	2,160			(200		)	1,960		200		(200		)	—
		$	114,239		$	(46,108	)	$	68,131	$	63,126	$	(41,848	)	$	21,278
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):
	2014	$	8,385
	2015	8,372
	2016	8,372
	2017	5,954
	2018	4,554
		$	35,637
Schedule Of Accrued Liabilities	'
	Accrued liabilities consist of the following (in thousands):
		September 30,
		2013			2012
	Payroll and benefits	$	73,461		$	61,720
	Sales and marketing	3,746			4,407
	Income tax accruals	4,196			8,621
	Other	11,205			11,661
		$	92,608		$	86,409

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2013
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,
		2013			2012			2011
	United States	$	431,833		$	421,346		$	342,741
	International	6,259			10,868			18,010
		$	438,092		$	432,214		$	360,751
Schedule Of Provision For Income Taxes (Benefit)	'
	The provision for income taxes (benefit) consists of the following (in thousands):
		Years Ended September 30,
		2013			2012			2011
	Current
	U.S. federal	$	138,372		$	147,774		$	103,620
	State	14,322			10,733			7,397
	Foreign	6,633			4,218			5,743
	Total	159,327			162,725			116,760
	Deferred
	U.S. federal	1,310			(7,320		)	3,070
	State	(203		)	187			(144		)
	Foreign	344			1,436			(332		)
	Total	1,451			(5,697		)	2,594
		$	160,778		$	157,028		$	119,354
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,
		2013			2012			2011
	Income tax provision at statutory rate	$	153,332		$	151,275		$	126,263
	State taxes, net of federal benefit	10,944			8,733			5,365
	Foreign operations	4,786			1,850			(971		)
	Research and development and other credits	(10,649		)	(3,537		)	(11,860		)
	Domestic manufacturing deduction	(14,047		)	(12,539		)	(9,351		)
	Stock-based and other compensation	15,286			10,501			9,388
	Other	1,126			745			520
		$	160,778		$	157,028		$	119,354
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,
		2013			2012
	Deferred tax assets
	Net operating loss carry-forwards	$	10,072		$	1,366
	Allowance for doubtful accounts	1,112			1,106
	Accrued compensation and benefits	7,272			6,371
	Inventories and related reserves	1,120			1,223
	Stock-based compensation	5,933			11,713
	Deferred revenue	26,277			23,372
	Other accruals and reserves	10,131			9,594
	Tax credit carry-forwards	2,122			793
		64,039			55,538
	Valuation allowance	(5,390		)	(208		)
		58,649			55,330
	Deferred tax liabilities
	Purchased intangibles and other	(21,567		)	(6,329		)
	Depreciation	(3,697		)	(3,161		)
		(25,264		)	(9,490		)
	Net deferred tax assets	$	33,385		$	45,840
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 2013, 2012 and 2011:
		2013			2012			2011
	Balance, beginning of period	$	5,452		$	5,952		$	6,568
	Gross increases (decreases) related to prior period tax positions	1,089			(201		)	1,198
	Gross increases related to current period tax positions	1,957			702			1,659
	Decreases relating to settlements with tax authorities	—			(3		)	(243		)
	Reductions due to lapses of statute of limitations	(1,196		)	(998		)	(3,230		)
	Balance, end of period	$	7,302		$	5,452		$	5,952

StockBased_Compensation_Tables

Stock-Based Compensation (Tables)	12 Months Ended
	Sep. 30, 2013
Share-based Compensation [Abstract]	'
Schedule Of Summary Of Restricted Stock Unit Activity	'
	A summary of restricted stock unit activity under the 2005 Plan is as follows:
			Outstanding		Weighted
			Stock Units		Average
					Grant Date
					Fair Value
	Balance, September 30, 2012		1,717,444		$	95.43
	Units granted		456,837		89.38
	Units vested		(1,078,607	)	89.31
	Units cancelled		(169,639	)	94.16
	Balance, September 30, 2013		926,035		$	95.47
Schedule Of Stock Option Activity	'
	A summary of stock option activity under all of the Company’s plans is as follows:
			Options Outstanding
			Number of		Weighted
			Shares		Average
					Exercise Price
					per Share
	Balance, September 30, 2012		284,474		$	11.73
	Options granted		52,397		1.32
	Options exercised		(125,701	)	10.67
	Options cancelled		(951	)	3.95
	Balance, September 30, 2013		210,219		$	9.8
Schedule Of Outstanding Stock Options Currently Exercisable, Vested And Expected To Vest	'
			Number of		Weighted		Weighted		Aggregate
			Shares		Average		Average		Intrinsic
					Remaining		Exercise		Value(1)
					Contractual		Price
					Life (in Years)		per Share
									(In thousands)
	Stock options outstanding		210,219		4.37		$	9.8	$	15,967
	Exercisable		140,054		2.46		$	13.48	$	10,123
	Vested and expected to vest		204,688		4.27		$	10.01	$	15,506
	-1	Aggregate intrinsic value represents the difference between the fair value of the Company’s common stock underlying these options at September 30, 2013 and the related exercise prices.
Schedule Of Equity Based Awards (Including Stock Options And Restricted Stock Units)	'
	As of September 30, 2013, equity based awards (including stock options and restricted stock units) are available for future issuance as follows:
			Awards
			Available for
			Grant
	Balance, September 30, 2012		2,422,360
	Granted		(609,234	)
	Cancelled		172,324
	Additional shares reserved (terminated), net		213,286
	Balance, September 30, 2013		2,198,736

Commitment_And_Contingencies_T

Commitment And Contingencies (Tables)	12 Months Ended
	Sep. 30, 2013
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		Sublease		Net Lease
		Payments		Income		Payments
	2014	23,714		4,013		19,701
	2015	19,741		4,028		15,713
	2016	17,192		3,993		13,199
	2017	17,022		4,102		12,920
	2018	15,293		2,770		12,523
	Thereafter	42,279		—		42,279
		$	135,241	$	18,906	$	116,335

Geographic_Sales_And_Significa1

Geographic Sales And Significant Customers (Tables)	12 Months Ended
	Sep. 30, 2013
Segments, Geographical Areas [Abstract]	'
Schedule Of Revenues By Geographic Region	'
	The following presents revenues by geographic region (in thousands):
		Years Ended September 30,
		2013		2012		2011
	Americas:
	United States	$	777,516	$	729,238	$	627,806
	Other	74,391		64,144		49,062
	Total Americas	851,907		793,382		676,868
	EMEA	327,109		294,191		240,453
	Japan	83,051		90,521		74,824
	Asia Pacific	219,247		199,153		159,689
		$	1,481,314	$	1,377,247	$	1,151,834

Quarterly_Results_Of_Operation1

Quarterly Results Of Operations (Tables)	12 Months Ended
	Sep. 30, 2013
Quarterly Financial Data [Abstract]	'
Schedule Of Quarterly Results Of Operations	'
		Three Months Ended
		Sept. 30, 2013		30-Jun-13		31-Mar-13		Dec. 31, 2012		Sept. 30, 2012		30-Jun-12		31-Mar-12		Dec. 31, 2011
		(Unaudited and in thousands, except per share data)
	Net revenues
	Products	$	212,291	$	196,746	$	185,107	$	204,712	$	209,718	$	207,118	$	205,165	$	196,554
	Services	183,038		173,556		165,125		160,739		152,841		145,516		134,457		125,878
	Total	395,329		370,302		350,232		365,451		362,559		352,634		339,622		322,432
	Cost of net revenues
	Products	35,151		32,350		29,773		31,792		35,752		34,482		33,668		33,200
	Services	31,792		32,567		30,529		29,093		26,929		25,805		23,926		22,406
	Total	66,943		64,917		60,302		60,885		62,681		60,287		57,594		55,606
	Gross profit	328,386		305,385		289,930		304,566		299,878		292,347		282,028		266,826
	Operating expenses
	Sales and marketing	119,836		121,906		119,031		122,268		116,298		112,064		110,995		106,238
	Research and development	54,464		54,075		52,534		48,541		47,731		46,985		43,568		39,122
	General and administrative	26,512		25,327		25,889		24,673		24,015		23,298		22,785		21,677
	Loss on facility sublease	2,393		—		—		—		—		—		—		—
	Total operating expenses	203,205		201,308		197,454		195,482		188,044		182,347		177,348		167,037
	Income from operations	125,181		104,077		92,476		109,084		111,834		110,000		104,680		99,789
	Other income, net	732		2,874		2,118		1,550		909		1,713		1,428		1,861
	Income before income taxes	125,913		106,951		94,594		110,634		112,743		111,713		106,108		101,650
	Provision for income taxes	49,682		38,773		31,182		41,141		45,026		39,377		37,467		35,158
	Net income	$	76,231	$	68,178	$	63,412	$	69,493	$	67,717	$	72,336	$	68,641	$	66,492
	Net income per share — basic	$	0.97	$	0.87	$	0.81	$	0.88	$	0.86	$	0.91	$	0.87	$	0.84
	Weighted average shares — basic	78,353		78,516		78,601		78,789		78,980		79,135		79,156		79,272
	Net income per share — diluted	$	0.97	$	0.86	$	0.8	$	0.88	$	0.85	$	0.91	$	0.86	$	0.83
	Weighted average shares — diluted	78,674		78,864		79,114		79,278		79,425		79,655		79,775		79,822

Summary_Of_Significant_Account3

Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)

0 Months Ended

12 Months Ended

0 Months Ended

Apr. 24, 2013

Nov. 15, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2011

Sep. 17, 2013

Sep. 30, 2013

Sep. 30, 2012

Minimum [Member]

Maximum [Member]

Hardware [Member]

Accounts Receivable [Member]

Accounts Receivable [Member]

Accounts Receivable [Member]

Computer Software, Intangible Asset [Member]

Computer Software, Intangible Asset [Member]

Computer Software, Intangible Asset [Member]

Computer Software, Intangible Asset [Member]

Computer Software, Intangible Asset [Member]

Computer Software, Intangible Asset [Member]

Avnet Technology Solutions [Member]

Ingram Micro Inc [Member]

Ingram Micro Inc [Member]

Versafe [Member]

Versafe [Member]

Traffix Systems [Member]

Concentration of Credit Risk

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Concentration risk percentage

'

'

'

'

'

'

'

'

13.40%

18.60%

12.00%

'

'

'

'

'

'

Other Assets

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Acquired and developed technology and customer relationship assets estimated useful lives

'

'

'

'

'

'

'

'

'

'

'

'5 years

'

'

'5 years

'

'

Acquired technology in connection with the acquisitions

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$15,400,000

$14,900,000

Amortization expense related to acquired technology

'

'

'

'

'

'

'

'

'

'

'

3,800,000

5,300,000

3,100,000

'

'

'

Revenue Recognition

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Domestic accounts receivable terms of payment

'

'

'

'

'

'30 days

'45 days

'

'

'

'

'

'

'

'

'

'

International accounts receivable terms of payment

'

'

'

'

'

'30 days

'120 days

'

'

'

'

'

'

'

'

'

'

VSOE Percentage Which Constitutes Substantial Majority of Transactions Priced Within a Narrow Range

'

'

80.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Range of VSOE to median sales price

'

'

15.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Guarantees and Product Warranties

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Standard product warranty period

'

'

'

'

'

'

'

'1 year

'

'

'

'

'

'

'

'

'

Advertising

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Advertising costs

'

'

2,800,000

1,800,000

2,200,000

'

'

'

'

'

'

'

'

'

'

'

'

Common Stock Repurchase

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Common stock share repurchase program, amount authorized

200,000,000

'

600,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares repurchased and retired

'

12,289,015

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Shares repurchased and retired, average price per share

'

$72.18

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock repurchase program, remaining amount

'

$112,500,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Summary_Of_Significant_Account4

Summary Of Significant Accounting Policies (Schedule Of Inventories) (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012
In Thousands, unless otherwise specified
Accounting Policies [Abstract]	'	'
Finished goods	$13,509	$13,565
Raw materials	5,517	3,845
Inventories, Total	$19,026	$17,410

Summary_Of_Significant_Account5

Summary Of Significant Accounting Policies (Property And Equipment) (Details) (USD $)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Property, Plant and Equipment [Line Items]	'	'	'
Computer equipment	$93,326,000	$95,987,000	'
Office furniture and equipment	13,391,000	12,335,000	'
Leasehold improvements	54,972,000	43,957,000	'
Property and equipment, gross	161,689,000	152,279,000	'
Accumulated depreciation and amortization	-98,167,000	-92,675,000	'
Property and equipment, net	63,522,000	59,604,000	'
Depreciation and amortization expense	$22,300,000	$19,000,000	$16,600,000
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_Account6

Summary Of Significant Accounting Policies (Stock-Based Compensation) (Details) (USD $)	0 Months Ended	12 Months Ended			1 Months Ended
	Oct. 29, 2013	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011	Nov. 30, 2011	Aug. 31, 2011	Aug. 31, 2010	Aug. 31, 2010	Nov. 30, 2012	Nov. 30, 2011	Aug. 31, 2011
					Annual Equity Program [Member]	Annual Equity Program [Member]	Annual Equity Program [Member]	Retention Awards Program [Member]	Annual Equity Program [Member]	Annual Equity Program [Member]	Annual Equity Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Stock-based compensation	'	$104,212,000	$95,348,000	$89,747,000	'	'	'	'	'	'	'
Unrecognized stock-based compensation cost	'	$82,500,000	'	'	'	'	'	'	'	'	'
Unrecognized stock-based compensation cost, period for recognition, years	'	'2 years	'	'	'	'	'	'	'	'	'
Approved RSUs to employees and executive officers pursuant to the Company's annual equity awards program	1,467,871	'	'	'	'	170,390	181,334	83,000	290,415	82,968	'
ESSP option, offering period	'	'6 months	'	'	'	'	'	'	'	'	'
Estimated forfeiture rate for grants awarded to executive officers and board of directors	'	7.00%	'	'	'	'	'	'	'	'	'
Estimated forfeiture rate for grants awarded to all other employees	'	8.00%	'	'	'	'	'	'	'	'	'
Percentage of the aggregate number of RSUs granted that vest in equal quarterly increments	'	'	'	'	50.00%	50.00%	50.00%	'	50.00%	'	'
Annual equity awards program vesting period	'	'	'	'	'3 years	'3 years	'3 years	'	'4 years	'	'
Portion of RSU grant subject to Company achieving specified quarterly revenue and EBITDA goals	'	'	'	'	'	'	'	'	0.125	0.167	0.167
Percentage of quarterly performance stock grant based on achieving quarterly revenue goal	'	'	'	'	'	'	'	'	50.00%	'	'
Percentage of quarterly performance stock grant based on achieving EBITDA goal	'	'	'	'	'	'	'	'	50.00%	'	'
Percentage of over-achievement threshold to which the goals are entitled	'	'	'	'	'	'	'	'	100.00%	'	'
Percentage of annual equity awards RSU grant subject to performance based vesting	'	'	'	'	33.33%	33.33%	'	'	37.50%	'	'
Percentage of annual equity awards RSU grant subject to performance based vesting in each period	'	'	'	'	16.66%	16.66%	'	'	12.50%	'	'
Percentage of quarterly revenue goal to be achieved for performance stock grant	'	'	'	'	'	'	'	'	80.00%	'	'
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%	'	'
Fair Value Assumptions	'	'	'	'	'	'	'	'	'	'	'
Risk-free interest rate	'	0.06%	0.14%	0.10%	'	'	'	'	'	'	'
Expected dividend	'	0.00%	0.00%	0.00%	'	'	'	'	'	'	'
Expected term	'	'6 months	'6 months	'6 months	'	'	'	'	'	'	'
Expected volatility	'	42.92%	45.20%	53.87%	'	'	'	'	'	'	'

Summary_Of_Significant_Account7

Summary Of Significant Accounting Policies (Schedule Of Computation Of Basic And Diluted Net Income Per Share) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Accounting Policies [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Net income	$76,231	$68,178	$63,412	$69,493	$67,717	$72,336	$68,641	$66,492	$277,314	$275,186	$241,397
Weighted average shares outstanding - basic	78,353	78,516	78,601	78,789	78,980	79,135	79,156	79,272	78,565	79,135	80,658
Dilutive effect of common shares from stock options and restricted stock units	'	'	'	'	'	'	'	'	571	645	824
Weighted average shares outstanding - diluted	78,674	78,864	79,114	79,278	79,425	79,655	79,775	79,822	79,136	79,780	81,482
Basic net income per share (USD per share)	$0.97	$0.87	$0.81	$0.88	$0.86	$0.91	$0.87	$0.84	$3.53	$3.48	$2.99
Diluted net income per share (USD per share)	$0.97	$0.86	$0.80	$0.88	$0.85	$0.91	$0.86	$0.83	$3.50	$3.45	$2.96

Fair_Value_Measurements_Schedu

Fair Value Measurements (Schedule Of Financial Assets Measured At Fair Value On A Recurring Basis) (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]	'	'
Cash equivalents, fair value	$13,145	$35,658
Available-for-sale securities	1,081,431	'
Financial assets measured at fair value on a recurring basis, total	1,094,576	1,019,431
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	13,145	35,658
Financial assets measured at fair value on a recurring basis, total	13,145	35,658
Significant Other Observable Inputs (Level 2) [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]	'	'
Financial assets measured at fair value on a recurring basis, total	1,078,395	979,023
Significant Unobservable Inputs (Level 3) [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]	'	'
Financial assets measured at fair value on a recurring basis, total	3,036	4,750
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	'	3,533
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	'	3,533
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	125,212	193,990
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	125,212	193,990
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	72,164	63,422
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	72,164	63,422
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	5,000	'
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	5,000	'
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	150,074	60,025
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	150,074	60,025
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	260,318	229,441
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	260,318	229,441
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	24,371	30,307
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	24,371	30,307
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	14,798	4,995
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	14,798	4,995
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	426,458	393,310
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	426,458	393,310
Long-Term Investments [Member] | Auction Rate Securities [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]	'	'
Available-for-sale securities	3,036	4,750
Long-Term Investments [Member] | Auction Rate Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]	'	'
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis, Valuation Techniques [Line Items]	'	'
Available-for-sale securities	$3,036	$4,750

Fair_Value_Measurements_Schedu1

Fair Value Measurements (Schedule Of Reconciliation Of Items Measured At Fair Value On A Recurring Basis That Used Significant Unobservable Inputs (Level 3)) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Balance, beginning of period	$4,750	$13,010
Total (losses) gains realized or unrealized: Included in other comprehensive income	-14	1,740
Settlements	-1,700	-10,000
Balance, end of period	3,036	4,750
Unrealized (losses) gains attributable to assets still held as of the end of the period	($14)	$112

ShortTerm_And_LongTerm_Investm2

Short-Term And Long-Term Investments (Schedule Of Short-Term And Long-Term Investments) (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012
In Thousands, unless otherwise specified
Schedule of Investments [Line Items]	'	'
Cost or Amortized Cost	$1,081,541	'
Fair Value	1,081,431	'
Short-Term Investments [Member]	'	'
Schedule of Investments [Line Items]	'	'
Cost or Amortized Cost	352,193	320,457
Gross Unrealized Gains	285	563
Gross Unrealized Losses	-28	-50
Fair Value	352,450	320,970
Long-Term Investments [Member]	'	'
Schedule of Investments [Line Items]	'	'
Cost or Amortized Cost	729,348	661,557
Gross Unrealized Gains	744	1,602
Gross Unrealized Losses	-1,111	-356
Fair Value	728,981	662,803
Certificates of Deposit [Member] | Short-Term Investments [Member]	'	'
Schedule of Investments [Line Items]	'	'
Cost or Amortized Cost	'	3,528
Gross Unrealized Gains	'	5
Gross Unrealized Losses	'	0
Fair Value	'	3,533
Corporate Bonds And Notes [Member] | Short-Term Investments [Member]	'	'
Schedule of Investments [Line Items]	'	'
Cost or Amortized Cost	125,010	193,548
Gross Unrealized Gains	210	482
Gross Unrealized Losses	-8	-40
Fair Value	125,212	193,990
Corporate Bonds And Notes [Member] | Long-Term Investments [Member]	'	'
Schedule of Investments [Line Items]	'	'
Cost or Amortized Cost	260,345	228,438
Gross Unrealized Gains	363	1,063
Gross Unrealized Losses	-390	-60
Fair Value	260,318	229,441
Municipal Bonds And Notes [Member] | Short-Term Investments [Member]	'	'
Schedule of Investments [Line Items]	'	'
Cost or Amortized Cost	72,116	63,371
Gross Unrealized Gains	58	61
Gross Unrealized Losses	-10	-10
Fair Value	72,164	63,422
Municipal Bonds And Notes [Member] | Long-Term Investments [Member]	'	'
Schedule of Investments [Line Items]	'	'
Cost or Amortized Cost	24,332	30,177
Gross Unrealized Gains	44	138
Gross Unrealized Losses	-5	-8
Fair Value	24,371	30,307
US Government Debt Securities [Member] | Short-Term Investments [Member]	'	'
Schedule of Investments [Line Items]	'	'
Cost or Amortized Cost	4,998	'
Gross Unrealized Gains	2	'
Gross Unrealized Losses	0	'
Fair Value	5,000	'
US Government Debt Securities [Member] | Long-Term Investments [Member]	'	'
Schedule of Investments [Line Items]	'	'
Cost or Amortized Cost	14,755	4,983
Gross Unrealized Gains	43	12
Gross Unrealized Losses	0	0
Fair Value	14,798	4,995
Auction Rate Securities [Member] | Long-Term Investments [Member]	'	'
Schedule of Investments [Line Items]	'	'
Cost or Amortized Cost	3,300	5,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	-264	-250
Fair Value	3,036	4,750
U.S. Government Agency Securities [Member] | Short-Term Investments [Member]	'	'
Schedule of Investments [Line Items]	'	'
Cost or Amortized Cost	150,069	60,010
Gross Unrealized Gains	15	15
Gross Unrealized Losses	-10	0
Fair Value	150,074	60,025
U.S. Government Agency Securities [Member] | Long-Term Investments [Member]	'	'
Schedule of Investments [Line Items]	'	'
Cost or Amortized Cost	426,616	392,959
Gross Unrealized Gains	294	389
Gross Unrealized Losses	-452	-38
Fair Value	$426,458	$393,310

ShortTerm_And_LongTerm_Investm3

Short-Term And Long-Term Investments (Schedule Of Amortized Cost And Fair Value Of Fixed Maturities By Contractual Years-To-Maturity) (Details) (USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified
Investments [Abstract]	'
Cost or Amortized Cost, Fixed Maturities, One year or less	$352,193
Cost or Amortized Cost, Fixed Maturities, Over one year	729,348
Cost or Amortized Cost	1,081,541
Fair Value, Fixed Maturities, One year or less	352,450
Fair Value, Fixed Maturities, Over one year	728,981
Fair Value	$1,081,431

ShortTerm_And_LongTerm_Investm4

Short-Term And Long-Term Investments (Schedule Of Investments That Have Been In A Continuous Unrealized Loss Position) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013
Schedule of Available-for-sale Securities [Line Items]	'
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months	508,997
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater	6,217
Fair Value, Continuous Loss Position, Unrealized Loss, Total	515,214
Gross Unrealized Losses, Continuous Loss Position, Less Than 12 Months	-874
Gross Unrealized Losses, Continuous Loss Position, 12 Months or Greater	-265
Gross Unrealized Losses, Continuous Loss Position, Total	-1,139
Corporate Bonds And Notes [Member]	'
Schedule of Available-for-sale Securities [Line Items]	'
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months	171,144
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater	3,181
Fair Value, Continuous Loss Position, Unrealized Loss, Total	174,325
Gross Unrealized Losses, Continuous Loss Position, Less Than 12 Months	-397
Gross Unrealized Losses, Continuous Loss Position, 12 Months or Greater	-1
Gross Unrealized Losses, Continuous Loss Position, Total	-398
Municipal Bonds And Notes [Member]	'
Schedule of Available-for-sale Securities [Line Items]	'
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months	20,080
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater	0
Fair Value, Continuous Loss Position, Unrealized Loss, Total	20,080
Gross Unrealized Losses, Continuous Loss Position, Less Than 12 Months	-15
Gross Unrealized Losses, Continuous Loss Position, 12 Months or Greater	0
Gross Unrealized Losses, Continuous Loss Position, Total	-15
Auction Rate Securities [Member]	'
Schedule of Available-for-sale Securities [Line Items]	'
Fair Value, Continuous Loss Position, Unrealized Loss, Less Than 12 Months	0
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater	3,036
Fair Value, Continuous Loss Position, Unrealized Loss, Total	3,036
Gross Unrealized Losses, Continuous Loss Position, Less Than 12 Months	0
Gross Unrealized Losses, Continuous Loss Position, 12 Months or Greater	-264
Gross Unrealized Losses, Continuous Loss Position, Total	-264
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	317,773
Fair Value, Continuous Loss Position, Unrealized Loss, 12 Months or Greater	0
Fair Value, Continuous Loss Position, Unrealized Loss, Total	317,773
Gross Unrealized Losses, Continuous Loss Position, Less Than 12 Months	-462
Gross Unrealized Losses, Continuous Loss Position, 12 Months or Greater	0
Gross Unrealized Losses, Continuous Loss Position, Total	-462
Minimum [Member]	'
Schedule of Available-for-sale Securities [Line Items]	'
Liquidity days for the securities provided by auction process	'7 days
Maximum [Member]	'
Schedule of Available-for-sale Securities [Line Items]	'
Liquidity days for the securities provided by auction process	'35 days

Business_Combinations_Acquisit

Business Combinations (Acquisition of LineRate Systems) (Details) (USD $)	12 Months Ended			0 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011	Feb. 11, 2013	Feb. 11, 2013	Feb. 11, 2013
				Line Rate Systems [Member]	In Process Research And Development [Member]	General and Administrative Expenses [Member]
					Line Rate Systems [Member]	Line Rate Systems [Member]
Business Acquisition [Line Items]	'	'	'	'	'	'
Acquisition of businesses, net of cash acquired	$212,642,000	$128,335,000	$0	$125,300,000	'	'
Business acquisition, transaction costs	'	'	'	'	'	300,000
Assets acquired	'	'	'	'	'	'
Cash	'	'	'	82,000	'	'
Current assets	'	'	'	556,000	'	'
Property and equipment, net	'	'	'	415,000	'	'
In-process research and development	'	'	'	29,853,000	29,900,000	'
Goodwill	523,727,000	348,239,000	234,691,000	99,560,000	'	'
Total assets acquired	'	'	'	130,466,000	'	'
Liabilities assumed	'	'	'	'	'	'
Accrued liabilities	'	'	'	-396,000	'	'
Deferred tax liabilities, net	'	'	'	-4,763,000	'	'
Total liabilities assumed	'	'	'	-5,159,000	'	'
Net assets acquired	'	'	'	$125,307,000	'	'
Amortization deduction period for acquisition purchase price recovery	'	'	'	'	'10 years	'
Discount rate	'	'	'	35.00%	'	'

Business_Combinations_Acquisit1

Business Combinations (Acquisition of Versafe Ltd) (Details) (USD $)	12 Months Ended			0 Months Ended	12 Months Ended	0 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011	Sep. 17, 2013	Sep. 30, 2013	Sep. 17, 2013	Sep. 17, 2013	Sep. 17, 2013
				Versafe [Member]	Developed Technology [Member]	Developed Technology [Member]	Customer Relationships [Member]	General and Administrative Expenses [Member]
						Versafe [Member]	Versafe [Member]	Versafe [Member]
Business Acquisition [Line Items]	'	'	'	'	'	'	'	'
Acquisition of businesses, net of cash acquired	$212,642,000	$128,335,000	$0	$91,700,000	'	'	'	'
Business acquisition, transaction costs	'	'	'	'	'	'	'	400,000
Assets acquired	'	'	'	'	'	'	'	'
Cash	'	'	'	4,020,000	'	'	'	'
Current assets	'	'	'	1,309,000	'	'	'	'
Property and equipment, net	'	'	'	41,000	'	'	'	'
Developed technology, customer relationships and other intangibles	'	'	'	21,260,000	'	15,400,000	5,900,000	'
Goodwill	523,727,000	348,239,000	234,691,000	75,937,000	'	'	'	'
Total assets acquired	'	'	'	102,567,000	'	'	'	'
Liabilities assumed	'	'	'	'	'	'	'	'
Accrued liabilities	'	'	'	-4,877,000	'	'	'	'
Deferred revenue	'	'	'	-611,000	'	'	'	'
Deferred tax liabilities, net	'	'	'	-5,335,000	'	'	'	'
Total liabilities assumed	'	'	'	10,823,000	'	'	'	'
Net assets acquired	'	'	'	$91,744,000	'	'	'	'
Discount rate	'	'	'	25.00%	'	'	'	'
Acquired and developed technology and customer relationship assets estimated useful lives	'	'	'	'	'5 years	'5 years	'	'
Weighted average useful life	'	'	'	'5 years 6 months	'	'	'	'

Balance_Sheet_Details_Schedule

Balance Sheet Details (Schedule Of Goodwill) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Goodwill [Roll Forward]	'	'
Goodwill, Beginning Balance	$348,239	$234,691
Other	-9	338
Goodwill, Ending Balance	523,727	348,239
Traffix Systems [Member]	'	'
Goodwill [Roll Forward]	'	'
Acquisition	'	113,210
Line Rate Systems [Member]	'	'
Goodwill [Roll Forward]	'	'
Acquisition	99,560	'
Versafe [Member]	'	'
Goodwill [Roll Forward]	'	'
Acquisition	$75,937	'

Balance_Sheet_Details_Schedule1

Balance Sheet Details (Schedule Of Other Assets) (Details) (USD $)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Balance Sheet Details [Abstract]	'	'	'
Acquired and developed technology and software development costs	$59,453,000	$18,129,000	'
Deposits and other	15,251,000	10,688,000	'
Restricted cash	860,000	179,000	'
Other assets	75,564,000	28,996,000	'
Amortization expense related to other assets	$4,300,000	$6,400,000	$4,300,000

Balance_Sheet_Details_Schedule2

Balance Sheet Details (Schedule Of Intangible Assets) (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012
In Thousands, unless otherwise specified
Finite-Lived Intangible Assets [Line Items]	'	'
Gross Carrying Amount	$114,239	$63,126
Accumulated Amortization	-46,108	-41,848
Net Carrying Amount	68,131	21,278
Developed Technology [Member]	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Gross Carrying Amount	99,463	54,240
Accumulated Amortization	-40,010	-36,111
Net Carrying Amount	59,453	18,129
Customer Relationships [Member]	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Gross Carrying Amount	8,399	5,379
Accumulated Amortization	-3,123	-2,855
Net Carrying Amount	5,276	2,524
Patents And Trademarks [Member]	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Gross Carrying Amount	3,044	3,044
Accumulated Amortization	-2,525	-2,464
Net Carrying Amount	519	580
Trade Names [Member]	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Gross Carrying Amount	1,173	263
Accumulated Amortization	-250	-218
Net Carrying Amount	923	45
Non-Compete Covenants [Member]	'	'
Finite-Lived Intangible Assets [Line Items]	'	'
Gross Carrying Amount	2,160	200
Accumulated Amortization	-200	-200
Net Carrying Amount	$1,960	$0

Balance_Sheet_Details_Schedule3

Balance Sheet Details (Schedule Of Estimated Amortization Expense For Intangible Assets) (Details) (USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified
Balance Sheet Details [Abstract]	'
2014	$8,385
2015	8,372
2016	8,372
2017	5,954
2018	4,554
Total estimated amortization expense	$35,637

Balance_Sheet_Details_Schedule4

Balance Sheet Details (Schedule Of Accrued Liabilities) (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012
In Thousands, unless otherwise specified
Balance Sheet Details [Abstract]	'	'
Payroll and benefits	$73,461	$61,720
Sales and marketing	3,746	4,407
Income tax accruals	4,196	8,621
Other	11,205	11,661
Total accrued liabilities	$92,608	$86,409

Income_Taxes_Narrative_Details

Income Taxes (Narrative) (Details) (USD $)	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Operating Loss Carryforwards [Line Items]	'	'	'
Undistributed earnings from international subsidiaries	$22,900,000	'	'
Interest expense related to uncertain tax positions	244,000	250,000	283,000
Unrecognized tax benefits, interest expenses accrued	431,000	406,000	'
Foreign [Member]	'	'	'
Operating Loss Carryforwards [Line Items]	'	'	'
Operating loss carry-forwards, net	43,300,000	'	'
Federal [Member]	'	'	'
Operating Loss Carryforwards [Line Items]	'	'	'
Operating loss carry-forwards, net	$13,000,000	'	'

Income_Taxes_Components_Of_Inc

Income Taxes (Components Of Income Before Income Taxes) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Income Tax Disclosure [Abstract]	'	'	'	'	'	'	'	'	'	'	'
United States	'	'	'	'	'	'	'	'	$431,833	$421,346	$342,741
International	'	'	'	'	'	'	'	'	6,259	10,868	18,010
Income before income taxes	$125,913	$106,951	$94,594	$110,634	$112,743	$111,713	$106,108	$101,650	$438,092	$432,214	$360,751

Income_Taxes_Schedule_Of_Provi

Income Taxes (Schedule Of Provision For Income Taxes (Benefit)) (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Income Tax Disclosure [Abstract]	'	'	'	'	'	'	'	'	'	'	'
Current, U.S. federal	'	'	'	'	'	'	'	'	$138,372	$147,774	$103,620
Current, State	'	'	'	'	'	'	'	'	14,322	10,733	7,397
Current, Foreign	'	'	'	'	'	'	'	'	6,633	4,218	5,743
Total	'	'	'	'	'	'	'	'	159,327	162,725	116,760
Deferred, U.S. federal	'	'	'	'	'	'	'	'	1,310	-7,320	3,070
Deferred, State	'	'	'	'	'	'	'	'	-203	187	-144
Deferred, Foreign	'	'	'	'	'	'	'	'	344	1,436	-332
Total	'	'	'	'	'	'	'	'	1,451	-5,697	2,594
Income taxes (benefit)	$49,682	$38,773	$31,182	$41,141	$45,026	$39,377	$37,467	$35,158	$160,778	$157,028	$119,354

Income_Taxes_Schedule_Of_Effec

Income Taxes (Schedule Of Effective Tax Rate Differs From The U.S. Federal Statutory Rate) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Income Tax Disclosure [Abstract]	'	'	'
Income tax provision at statutory rate	$153,332	$151,275	$126,263
State taxes, net of federal benefit	10,944	8,733	5,365
Foreign operations	4,786	1,850	-971
Research and development and other credits	-10,649	-3,537	-11,860
Domestic manufacturing deduction	-14,047	-12,539	-9,351
Stock-based and other compensation	15,286	10,501	9,388
Other	1,126	745	520
Income taxes (benefit)	$160,778	$157,028	$119,354

Income_Taxes_Schedule_Of_Tax_E

Income Taxes (Schedule Of Tax Effects To Deferred Tax Assets And Liabilities) (Details) (USD $)	Sep. 30, 2013	Sep. 30, 2012
In Thousands, unless otherwise specified
Income Tax Disclosure [Abstract]	'	'
Net operating loss carry-forwards	$10,072	$1,366
Allowance for doubtful accounts	1,112	1,106
Accrued compensation and benefits	7,272	6,371
Inventories and related reserves	1,120	1,223
Stock-based compensation	5,933	11,713
Deferred revenue	26,277	23,372
Other accruals and reserves	10,131	9,594
Tax credit carry-forwards	2,122	793
Total deferred tax assets before deferred liabilities	64,039	55,538
Valuation allowance	-5,390	-208
Deferred tax assets, net of valuation allowance	58,649	55,330
Purchased intangibles and other	-21,567	-6,329
Depreciation	-3,697	-3,161
Total deferred tax liabilities	-25,264	-9,490
Net deferred tax assets	$33,385	$45,840

Income_Taxes_Schedule_Of_Recon

Income Taxes (Schedule Of Reconciliation Of Beginning And Ending Amount Of Unrecognized Tax Benefits) (Details) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'	'	'
Balance, beginning of period	$5,452	$5,952	$6,568
Gross increases (decreases) related to prior period tax positions	1,089	-201	1,198
Gross increases related to current period tax positions	1,957	702	1,659
Decreases relating to settlements with tax authorities	0	-3	-243
Reductions due to lapses of statute of limitations	-1,196	-998	-3,230
Balance, end of period	$7,302	$5,452	$5,952

StockBased_Compensation_Narrat

Stock-Based Compensation (Narrative) (Details) (USD $)

0 Months Ended

12 Months Ended

1 Months Ended

1 Months Ended

12 Months Ended

12 Months Ended

Oct. 29, 2013

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Jul. 31, 2003

Sep. 30, 2013

Jul. 31, 2004

Sep. 30, 2013

Sep. 30, 2007

Feb. 29, 2012

Sep. 30, 2013

Sep. 30, 2013

Mar. 31, 2013

Feb. 28, 2013

Sep. 30, 2013

Sep. 30, 2013

Mar. 31, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2011

Sep. 30, 2013

Sep. 30, 2013

1998 Equity Incentive Plan [Member]

2011 Employee Stock Purchase Plan [Member]

2000 Equity Incentive Plan [Member]

uRoam Acquisition Equity Incentive Plan [Member]

uRoam Acquisition Equity Incentive Plan [Member]

MagniFire Acquisition Equity Incentive Plan [Member]

MagniFire Acquisition Equity Incentive Plan [Member]

Acopia Plan [Member]

Acopia Plan [Member]

Traffix Plan [Member]

Traffix Plan [Member]

Traffix 2007 Plan [Member] [Member]

Traffix 2007 Plan [Member] [Member]

LineRate Acquisition Plan [Member]

LineRate Acquisition Plan [Member]

LineRate 2009 Plan [Member] [Member]

LineRate 2009 Plan [Member] [Member]

Versafe Acquisition Plan [Member]

2005 Equity Incentive Plan [Member]

Stock Options [Member]

Restricted Stock Unit [Member]

Restricted Stock Unit [Member]

Restricted Stock Unit [Member]

Minimum [Member]

Maximum [Member]

Restricted Stock Unit [Member]

Restricted Stock Unit [Member]

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Annual equity awards program vesting period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'2 years

'2 years

'2 years

'1 year

'4 years

Restricted stock units vesting period in years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'2 years

'2 years

'2 years

'1 year

'4 years

Stock option expiration period from date of grant

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'10 years

'

'

'

'

'

Vesting rate of stock options and awards upon certain changes in ownership control

'

'

'

'

50.00%

'

50.00%

'

'

'

'

'

'

50.00%

'

'

'

50.00%

'

'

'

50.00%

50.00%

'

'

'

'

'

'

Shares available for purchase under stock option plan

'

'

'

'

52,753

'

40,958

1,650

'

2,690

'

12,509

'

'

'

56,758

'

'

'

42,901

'

'

'

'

'

'

'

'

'

Common stock reserved for issuance

'

'

'

'

'

6,000,000

7,000,000

'

500,000

'

830,000

'

2,230,703

75,000

'

'

106,829

100,000

'

'

201,478

60,000

12,400,000

'

'

'

'

'

'

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

'6 months

'6 months

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Percentage of common stock lesser of the fair market value

'

'

'

'

'

85.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Stock units issued

1,467,871

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

456,837

'

'

'

'

Outstanding stock units

'

'

'

'

'

'

'

'

'

'

'

'

'

'

33,693

'

'

'

100,000

'

'

'

926,035

'

926,035

1,717,444

'

'

'

Stock options issued during period

'

52,397

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

52,397

'

'

'

'

'

'

'

'

'

Restricted stock units issued

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100,000

'

'

'

456,837

'

'

'

'

'

'

Shares available for award

'

'

'

'

'

1,014,179

'

'

'

'

'

'

'

'

'

'

'

'

'

3,574

'

60,000

2,135,162

'

'

'

'

'

'

Weighted average fair value of restricted stock units granted

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$86.69

$99.63

$94.99

'

'

Fair market value of restricted stock vested

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

97,500,000

93,800,000

145,000,000

'

'

Total intrinsic value of options exercised

'

$9,800,000

$13,200,000

$15,200,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

StockBased_Compensation_Schedu

Stock-Based Compensation (Schedule Of Summary Of Restricted Stock Unit Activity) (Details) (USD $)	0 Months Ended	12 Months Ended
	Oct. 29, 2013	Sep. 30, 2013
		Restricted Stock Unit [Member]
Outstanding Stock Units	'	'
Outstanding Stock Units, Beginning balance	'	1,717,444
Outstanding Stock Units, Units granted	1,467,871	456,837
Outstanding Stock Units, Units vested	'	-1,078,607
Outstanding Stock Units, Units cancelled	'	-169,639
Outstanding Stock Units, Ending balance	'	926,035
Weighted Average Grant Date Fair Value	'	'
Weighted Average Grant Date Fair Value, Beginning balance	'	$95.43
Weighted Average Grant Date Fair Value, Units granted	'	$89.38
Weighted Average Grant Date Fair Value, Units vested	'	$89.31
Weighted Average Grant Date Fair Value, Units cancelled	'	$94.16
Weighted Average Grant Date Fair Value, Ending balance	'	$95.47

StockBased_Compensation_Schedu1

Stock-Based Compensation (Schedule Of Stock Option Activity) (Details) (USD $)	12 Months Ended
	Sep. 30, 2013
Number of Shares	'
Number of Shares, Beginning balance	284,474
Number of Shares, Options granted	52,397
Number of Shares, Options exercised	-125,701
Number of Shares, Options cancelled	-951
Number of Shares, Ending balance	210,219
Weighted Average Exercise Price per Share	'
Weighted Average Exercise Price per Share, Beginning balance	$11.73
Weighted Average Exercise Price per Share, Options granted	$1.32
Weighted Average Exercise Price per Share, Options exercised	$10.67
Weighted Average Exercise Price per Share, Options cancelled	$3.95
Weighted Average Exercise Price per Share, Ending balance	$9.80

StockBased_Compensation_Schedu2

Stock-Based Compensation (Schedule Of Outstanding Stock Options Currently Exercisable, Vested And Expected To Vest) (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2012
Share-based Compensation [Abstract]	'		'
Stock options outstanding	210,219		284,474
Stock options outstanding, Weighted Average Remaining Contractual Life (in Years)	'4 years 4 months 13 days		'
Stock options outstanding, Weighted Average Exercise Price per Share	$9.80		$11.73
Stock options outstanding, Aggregate Intrinsic Value	$15,967	[1]	'
Exercisable, Number of Shares	140,054		'
Exercisable, Weighted Average Remaining Contractual Life (in Years)	'2 years 5 months 16 days		'
Exercisable, Weighted Average Exercise Price per Share	$13.48		'
Exercisable, Aggregate Intrinsic Value	10,123	[1]	'
Vested and expected to vest, Number of Shares	204,688		'
Vested and expected to vest, Weighted Average Remaining Contractual Life (in Years)	'4 years 3 months 7 days		'
Vested and expected to vest, Weighted Average Exercise Price per Share	$10.01		'
Vested and expected to vest, Aggregate Intrinsic Value	$15,506	[1]	'
[1]	Aggregate intrinsic value represents the difference between the fair value of the Company’s common stock underlying these options at September 30, 2013 and the related exercise prices.

StockBased_Compensation_Schedu3

Stock-Based Compensation (Schedule Of Equity Based Awards (Including Stock Options And Restricted Stock Units)) (Details)	0 Months Ended	12 Months Ended
	Oct. 29, 2013	Sep. 30, 2013
		Equity Based Awards [Member]
Awards Available for Grant	'	'
Awards Available for Grant, Beginning balance	'	2,422,360
Awards Available for Grant, Granted	-1,467,871	-609,234
Awards Available for Grant, Cancelled	'	172,324
Additional shares reserved (terminated), net	'	213,286
Awards Available for Grant, Ending balance	'	2,198,736

Commitments_And_Contingencies_

Commitments And Contingencies (Narrative) (Details) (USD $)

1 Months Ended

3 Months Ended

12 Months Ended

1 Months Ended

Aug. 31, 2013

Apr. 30, 2010

Sep. 30, 2013

Jun. 30, 2013

Mar. 31, 2013

Dec. 31, 2012

Sep. 30, 2012

Jun. 30, 2012

Mar. 31, 2012

Dec. 31, 2011

Sep. 30, 2013

Sep. 30, 2012

Sep. 30, 2011

Oct. 31, 2006

building

333 Elliott West [Member]

sqft

Commitments And Contingencies [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of buildings in the amended and restated lease

'

3

'

'

'

'

'

'

'

'

'

'

'

'

Expiration date

'

'

'

'

'

'

'

'

'

'

31-Dec-22

'

'

'

Office space occupied under lease agreement

'

'

'

'

'

'

'

'

'

'

'

'

'

137,000

Rent expense under non-cancelable operating leases

'

'

'

'

'

'

'

'

'

'

$26,500,000

$21,600,000

$19,000,000

'

Loss on facility sublease

2,393,000

'

2,393,000

0

0

0

0

0

0

0

2,393,000

0

0

'

Contract manufacturers' purchase obligations

'

'

$16,400,000

'

'

'

'

'

'

'

$16,400,000

'

'

'

Commitments_And_Contingencies_1

Commitments And Contingencies (Schedule Of Future Minimum Operating Lease Payments, Net Of Sublease Income) (Details) (USD $)	Sep. 30, 2013
In Thousands, unless otherwise specified
Gross Lease Payments	'
Gross Lease Payments, 2014	$23,714
Gross Lease Payments, 2015	19,741
Gross Lease Payments, 2016	17,192
Gross Lease Payments, 2017	17,022
Gross Lease Payments, 2018	15,293
Gross Lease Payments, Thereafter	42,279
Gross Lease Payments, Total	135,241
Sublease Income	'
Sublease Income, 2014	4,013
Sublease Income, 2015	4,028
Sublease Income, 2016	3,993
Sublease Income, 2017	4,102
Sublease Income, 2018	2,770
Sublease Income, Thereafter	0
Sublease Income, Total	18,906
Net Lease Payments	'
Net Lease Payments, 2014	19,701
Net Lease Payments, 2015	15,713
Net Lease Payments, 2016	13,199
Net Lease Payments, 2017	12,920
Net Lease Payments, 2018	12,523
Net Lease Payments, Thereafter	42,279
Net Lease Payments, Total	$116,335

Employee_Benefit_Plans_Details

Employee Benefit Plans (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Abstract]	'	'	'
Contributions by the Company to the plan	$6.40	$5.70	$4.70
Employer contribution, vesting period	'4 years	'	'

Geographic_Sales_And_Significa2

Geographic Sales And Significant Customers (Details) (USD $)	3 Months Ended								12 Months Ended
In Thousands, unless otherwise specified	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenue	$395,329	$370,302	$350,232	$365,451	$362,559	$352,634	$339,622	$322,432	$1,481,314	$1,377,247	$1,151,834
United States [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenue	'	'	'	'	'	'	'	'	777,516	729,238	627,806
Other Americas [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenue	'	'	'	'	'	'	'	'	74,391	64,144	49,062
Americas [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenue	'	'	'	'	'	'	'	'	851,907	793,382	676,868
EMEA [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenue	'	'	'	'	'	'	'	'	327,109	294,191	240,453
Japan [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenue	'	'	'	'	'	'	'	'	83,051	90,521	74,824
Asia Pacific [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Revenue	'	'	'	'	'	'	'	'	$219,247	$199,153	$159,689
Geographic Concentration Risk [Member] | Sales Revenue, Product Line [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Number of distributors	'	'	'	'	'	'	'	'	1	'	'
Geographic Concentration Risk [Member] | Accounts Receivable [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Number of distributors	'	'	'	'	'	'	'	'	1	2	'
Avnet Technology Solutions [Member] | Accounts Receivable [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Concentration risk percentage	'	'	'	'	'	'	'	'	'	13.40%	'
Ingram Micro Inc [Member] | Accounts Receivable [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Concentration risk percentage	'	'	'	'	'	'	'	'	18.60%	12.00%	'
Ingram Micro Inc [Member] | Geographic Concentration Risk [Member] | Sales Revenue, Product Line [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Concentration risk percentage	'	'	'	'	'	'	'	'	15.70%	13.80%	10.70%
Avnet Technology Solutions [Member] | Geographic Concentration Risk [Member] | Sales Revenue, Product Line [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Concentration risk percentage	'	'	'	'	'	'	'	'	16.60%	17.10%	18.10%
Worldwide Distributor3 [Member] | Geographic Concentration Risk [Member] | Sales Revenue, Product Line [Member]	'	'	'	'	'	'	'	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Concentration risk percentage	'	'	'	'	'	'	'	'	11.80%	'	'

Quarterly_Results_Of_Operation2

Quarterly Results Of Operations (Schedule Of Quarterly Results Of Operations) (Details) (USD $)	1 Months Ended	3 Months Ended								12 Months Ended
In Thousands, except Per Share data, unless otherwise specified	Aug. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Quarterly Financial Data [Abstract]	'	'	'	'	'	'	'	'	'	'	'	'
Products	'	$212,291	$196,746	$185,107	$204,712	$209,718	$207,118	$205,165	$196,554	$798,856	$818,555	$721,975
Services	'	183,038	173,556	165,125	160,739	152,841	145,516	134,457	125,878	682,458	558,692	429,859
Total	'	395,329	370,302	350,232	365,451	362,559	352,634	339,622	322,432	1,481,314	1,377,247	1,151,834
Products	'	35,151	32,350	29,773	31,792	35,752	34,482	33,668	33,200	129,066	137,102	129,325
Services	'	31,792	32,567	30,529	29,093	26,929	25,805	23,926	22,406	123,981	99,066	78,679
Total	'	66,943	64,917	60,302	60,885	62,681	60,287	57,594	55,606	253,047	236,168	208,004
Gross profit	'	328,386	305,385	289,930	304,566	299,878	292,347	282,028	266,826	1,228,267	1,141,079	943,830
Sales and marketing	'	119,836	121,906	119,031	122,268	116,298	112,064	110,995	106,238	483,041	445,595	370,735
Research and development	'	54,464	54,075	52,534	48,541	47,731	46,985	43,568	39,122	209,614	177,406	138,910
General and administrative	'	26,512	25,327	25,889	24,673	24,015	23,298	22,785	21,677	102,401	91,775	83,523
Loss on facility sublease	2,393	2,393	0	0	0	0	0	0	0	2,393	0	0
Total	'	203,205	201,308	197,454	195,482	188,044	182,347	177,348	167,037	797,449	714,776	593,168
Income from operations	'	125,181	104,077	92,476	109,084	111,834	110,000	104,680	99,789	430,818	426,303	350,662
Other income, net	'	732	2,874	2,118	1,550	909	1,713	1,428	1,861	7,274	5,911	10,089
Income before income taxes	'	125,913	106,951	94,594	110,634	112,743	111,713	106,108	101,650	438,092	432,214	360,751
Provision for income taxes	'	49,682	38,773	31,182	41,141	45,026	39,377	37,467	35,158	160,778	157,028	119,354
Net income	'	$76,231	$68,178	$63,412	$69,493	$67,717	$72,336	$68,641	$66,492	$277,314	$275,186	$241,397
Net income per share - basic (USD per share)	'	$0.97	$0.87	$0.81	$0.88	$0.86	$0.91	$0.87	$0.84	$3.53	$3.48	$2.99
Weighted average shares - basic (shares)	'	78,353	78,516	78,601	78,789	78,980	79,135	79,156	79,272	78,565	79,135	80,658
Net income per share - diluted (USD per share)	'	$0.97	$0.86	$0.80	$0.88	$0.85	$0.91	$0.86	$0.83	$3.50	$3.45	$2.96
Weighted average shares - diluted (shares)	'	78,674	78,864	79,114	79,278	79,425	79,655	79,775	79,822	79,136	79,780	81,482