Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2014		Sep. 30, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	$ 218,649	[1]	$ 197,166	[2]
Short-term investments	473,890		531,065
Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	38,467		50,742
Short-term investments	0		0
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	180,182		146,424
Short-term investments	473,890		531,065
Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0		0
Short-term investments	0		0
Acquisition-related contingent consideration
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Acquisition-related contingent consideration	1,594		3,182
Acquisition-related contingent consideration | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Acquisition-related contingent consideration	0		0
Acquisition-related contingent consideration | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Acquisition-related contingent consideration	0		0
Acquisition-related contingent consideration | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Acquisition-related contingent consideration	1,594		3,182
Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	2,001		9,095
Money market funds | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	2,001		9,095
Money market funds | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0		0
Money market funds | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0		0
Time deposits
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	36,466		41,647
Time deposits | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	36,466		41,647
Time deposits | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0		0
Time deposits | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0		0
Commercial paper
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	180,182		146,424
Short-term investments	290,090		385,223
Commercial paper | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0		0
Short-term investments	0		0
Commercial paper | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	180,182		146,424
Short-term investments	290,090		385,223
Commercial paper | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	0		0
Short-term investments	0		0
Certificates of deposit
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	126,914		96,833
Certificates of deposit | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	0		0
Certificates of deposit | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	126,914		96,833
Certificates of deposit | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	0		0
Other fixed income securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	56,886		49,009
Other fixed income securities | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	0		0
Other fixed income securities | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	56,886		49,009
Other fixed income securities | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term investments	0		0
Cash
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	$ 104,600		$ 104,500

[1] Included in cash and cash equivalents in the consolidated balance sheets as of March 31, 2014, in addition to $104.6 million of cash.

[2] Included in cash and cash equivalents in the consolidated balance sheets as of September 30, 2013, in addition to $104.5 million of cash.