Stock-Based Compensation (Narrative) (Details) (USD $)	12 Months Ended							1 Months Ended				1 Months Ended				12 Months Ended		12 Months Ended		12 Months Ended		12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2014 1998 Equity Incentive Plan [Member]	Sep. 30, 2014 2011 Employee Stock Purchase Plan [Member]	Sep. 30, 2014 Acopia Plan [Member]	Sep. 30, 2007 Acopia Plan [Member]	Feb. 29, 2012 Traffix Plan [Member]	Sep. 30, 2014 Traffix Plan [Member]	Sep. 30, 2014 Traffix 2007 Plan [Member] [Member]	Mar. 31, 2014 Traffix 2007 Plan [Member] [Member]	Feb. 28, 2013 LineRate Acquisition Plan [Member]	Sep. 30, 2014 LineRate Acquisition Plan [Member]	Sep. 30, 2014 LineRate 2009 Plan [Member] [Member]	Mar. 31, 2013 LineRate 2009 Plan [Member] [Member]	Sep. 30, 2014 Versafe Acquisition Plan [Member]	Sep. 30, 2013 Versafe Acquisition Plan [Member]	Sep. 30, 2014 Defense.Net Acquisition Equity Incentive Plan [Member]	Jun. 30, 2014 Defense.Net Acquisition Equity Incentive Plan [Member]	Sep. 30, 2014 Defense.Net, Inc. 2012 Stock Option and Grant Plan [Member]	Mar. 31, 2013 Defense.Net, Inc. 2012 Stock Option and Grant Plan [Member]	Sep. 30, 2014 2014 Equity Incentive Plan [Member]	Sep. 30, 2014 Stock Options [Member]	Sep. 30, 2014 Restricted Stock Unit [Member]	Sep. 30, 2013 Restricted Stock Unit [Member]	Sep. 30, 2012 Restricted Stock Unit [Member]	Sep. 30, 2014 Minimum [Member] Restricted Stock Unit [Member]	Sep. 30, 2014 Maximum [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%
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period																42,642		23,000		10,088		1,719,690
Shares available for purchase under stock option plan				6,800		11,853				19,464				22,877						9,774
Common stock reserved for issuance					6,000,000		2,230,703	75,000			106,829	100,000			201,478		60,000		30,000		84,375	15,380,000
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																								1,719,690
Outstanding stock units									20,156				68,773			35,892		23,000				1,290,782		1,290,782	926,035
Stock options issued during period	10,088
Shares available for award					498,605													7,000		46,757		3,565,538
Weighted average fair value of restricted stock units granted																								$ 83.81	$ 86.69	$ 99.63
Fair market value of restricted stock vested																								128,900,000	97,500,000	93,800,000
Total intrinsic value of options exercised	$ 14,100,000	$ 9,800,000	$ 13,200,000