Cash, cash equivalents, short-term investments, and marketable securities (Details 2) (USD $) In Thousands	Sep. 30, 2011
Schedule of available-for-sale investments at contractual maturities
Due within 1 year	$ 76,587
Due within 2 years	89,479
Total	166,066
Short-Term Municipal Bond Fund [Member]
Schedule of available-for-sale investments at contractual maturities
Due within 1 year	20,520
Due within 2 years	0
Total	20,520
Commercial Paper [Member]
Schedule of available-for-sale investments at contractual maturities
Due within 1 year	13,971
Due within 2 years	0
Total	13,971
Corporate Notes And Bonds [Member]
Schedule of available-for-sale investments at contractual maturities
Due within 1 year	42,096
Due within 2 years	76,325
Total	118,421
U.S. Government Agencies [Member]
Schedule of available-for-sale investments at contractual maturities
Due within 1 year	0
Due within 2 years	13,154
Total	$ 13,154

For an unclassified balance sheet, total of debt securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

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-Name Accounting Standards Codification

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Reference 2: http://www.xbrl.org/2003/role/presentationRef

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Reference 3: http://www.xbrl.org/2003/role/presentationRef

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Reference 4: http://www.xbrl.org/2003/role/presentationRef

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Reference 5: http://www.xbrl.org/2003/role/presentationRef

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Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 115

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 7: http://www.xbrl.org/2003/role/presentationRef

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 10: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

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+ Details