Income Taxes	9 Months Ended
Jun. 30, 2013
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The effective tax rate was 36.3% and 35.2% for the three months ended June 30, 2013 and 2012, respectively. The effective tax rate was 35.6% and 35.1% for the nine months ended June 30, 2013 and 2012, respectively. The increase in effective tax rate is primarily due to state income taxes. As of June 30, 2013, the Company has $6.3 million of unrecognized tax benefits that, if recognized, would affect the effective tax rate. It is reasonably possible that the Company’s existing liabilities for unrecognized tax benefits may change within the next twelve months primarily due to the expiration of statutes of limitations. The Company recognizes interest and, if applicable, penalties for any uncertain tax positions as a component of income tax expense. 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. 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 2011 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 fiscal year 2008 and 2009 state income tax returns, and the fiscal year 2010 federal income tax return.

Income Taxes

9 Months Ended

Jun. 30, 2013

The effective tax rate was 36.3% and 35.2% for the three months ended June 30, 2013 and 2012, respectively. The effective tax rate was 35.6% and 35.1% for the nine months ended June 30, 2013 and 2012, respectively. The increase in effective tax rate is primarily due to state income taxes.

As of June 30, 2013, the Company has $6.3 million of unrecognized tax benefits that, if recognized, would affect the effective tax rate. It is reasonably possible that the Company’s existing liabilities for unrecognized tax benefits may change within the next twelve months primarily due to the expiration of statutes of limitations. The Company recognizes interest and, if applicable, penalties for any uncertain tax positions as a component of income tax expense.

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. 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 2011 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 fiscal year 2008 and 2009 state income tax returns, and the fiscal year 2010 federal income tax return.