Quarterly Results Of Operations (Schedule Of Quarterly Results Of Operations) (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Quarterly Financial Data [Abstract]
Products	$ 255,461	$ 236,933	$ 225,135	$ 218,601	$ 212,291	$ 196,746	$ 185,107	$ 204,712	$ 936,130	$ 798,856	$ 818,555
Services	209,805	203,352	194,908	187,851	183,038	173,556	165,125	160,739	795,916	682,458	558,692
Total	465,266	440,285	420,043	406,452	395,329	370,302	350,232	365,451	1,732,046	1,481,314	1,377,247
Products	43,351	40,387	37,806	37,244	35,151	32,350	29,773	31,792	158,788	129,066	137,102
Services	38,601	39,075	37,856	35,639	31,792	32,567	30,529	29,093	151,171	123,981	99,066
Total	81,952	79,462	75,662	72,883	66,943	64,917	60,302	60,885	309,959	253,047	236,168
Gross profit	383,314	360,823	344,381	333,569	328,386	305,385	289,930	304,566	1,422,087	1,228,267	1,141,079
Sales and marketing	143,284	139,945	140,252	134,803	119,836	121,906	119,031	122,268	558,284	483,041	445,595
Research and development	65,401	67,026	67,232	64,133	54,464	54,075	52,534	48,541	263,792	209,614	177,406
General and administrative	27,148	27,773	26,033	25,500	26,512	25,327	25,889	24,673	106,454	102,401	91,775
Loss on facility sublease	0	0	0	0	2,393	0	0	0	0	2,393	0
Total	235,833	234,744	233,517	224,436	203,205	201,308	197,454	195,482	928,530	797,449	714,776
Income from operations	147,481	126,079	110,864	109,133	125,181	104,077	92,476	109,084	493,557	430,818	426,303
Other income, net	2,323	1,193	23	246	732	2,874	2,118	1,550	3,785	7,274	5,911
Income before income taxes	149,804	127,272	110,887	109,379	125,913	106,951	94,594	110,634	497,342	438,092	432,214
Provision for income taxes	55,783	47,799	41,246	41,331	49,682	38,773	31,182	41,141	186,159	160,778	157,028
Net income	$ 94,021	$ 79,473	$ 69,641	$ 68,048	$ 76,231	$ 68,178	$ 63,412	$ 69,493	$ 311,183	$ 277,314	$ 275,186
Net income per share - basic (USD per share)	$ 1.27	$ 1.06	$ 0.92	$ 0.88	$ 0.97	$ 0.87	$ 0.81	$ 0.88	$ 4.13	$ 3.53	$ 3.48
Weighted average shares - basic (shares)	73,817	74,812	75,508	77,438	78,353	78,516	78,601	78,789	75,395	78,565	79,135
Net income per share - diluted (USD per share)	$ 1.26	$ 1.05	$ 0.91	$ 0.87	$ 0.97	$ 0.86	$ 0.80	$ 0.88	$ 4.09	$ 3.50	$ 3.45
Weighted average shares - diluted (shares)	74,366	75,369	76,244	77,822	78,674	78,864	79,114	79,278	76,092	79,136	79,780