Short-Term and Long-Term Investments (Schedule of Short-Term and Long-Term Investments) (Details) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Sep. 30, 2012
Schedule of Investments [Line Items]
Cost or Amortized Cost	$ 1,069,265
Fair Value	1,067,376
Short-Term Investments [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	352,749	320,457
Gross Unrealized Gains	375	563
Gross Unrealized Losses	(79)	(50)
Fair Value	353,045	320,970
Long-Term Investments [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	716,516	661,557
Gross Unrealized Gains	376	1,602
Gross Unrealized Losses	(2,561)	(356)
Fair Value	714,331	662,803
Corporate Bonds and Notes [Member] | Short-Term Investments [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	154,949	193,548
Gross Unrealized Gains	274	482
Gross Unrealized Losses	(49)	(40)
Fair Value	155,174	193,990
Corporate Bonds and Notes [Member] | Long-Term Investments [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	231,182	228,438
Gross Unrealized Gains	231	1,063
Gross Unrealized Losses	(904)	(60)
Fair Value	230,509	229,441
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
Municipal Bonds and Notes [Member] | Short-Term Investments [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	63,795	63,371
Gross Unrealized Gains	71	61
Gross Unrealized Losses	(5)	(10)
Fair Value	63,861	63,422
Municipal Bonds and Notes [Member] | Long-Term Investments [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	29,049	30,177
Gross Unrealized Gains	33	138
Gross Unrealized Losses	(32)	(8)
Fair Value	29,050	30,307
Auction Rate Securities [Member] | Long-Term Investments [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	4,400	5,000
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(352)	(250)
Fair Value	4,048	4,750
U.S. Government Securities [Member] | Short-Term Investments [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	4,997
Gross Unrealized Gains	1
Gross Unrealized Losses	0
Fair Value	4,998
U.S. Government Securities [Member] | Long-Term Investments [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	12,348	4,983
Gross Unrealized Gains	10	12
Gross Unrealized Losses	0	0
Fair Value	12,358	4,995
U.S. Government Agency Securities [Member] | Short-Term Investments [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	129,008	60,010
Gross Unrealized Gains	29	15
Gross Unrealized Losses	(25)	0
Fair Value	129,012	60,025
U.S. Government Agency Securities [Member] | Long-Term Investments [Member]
Schedule of Investments [Line Items]
Cost or Amortized Cost	439,537	392,959
Gross Unrealized Gains	102	389
Gross Unrealized Losses	(1,273)	(38)
Fair Value	$ 438,366	$ 393,310