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Financial Instruments - Financial Instruments Measured on Recurring Basis (Detail) (USD $)
In Thousands, unless otherwise specified
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Sep. 30, 2012
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Dec. 31, 2011
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair value, available-for-sale securities |
$ 63,106
|
$ 72,082
|
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Fair Value Measurements Recurring [Member]
|
|
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair value, available-for-sale securities |
63,106
|
72,082
|
|
Money market funds [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
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| Fair value, available-for-sale securities |
9,695
|
14,372
|
|
Money market funds [Member] | Fair Value Measurements Recurring [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair value, available-for-sale securities |
9,695
|
14,372
|
|
Government debt securities [Member] | Fair Value Measurements Recurring [Member]
|
|
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
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| Fair value, available-for-sale securities |
3,002
|
15,969
|
|
Corporate debt securities [Member] | Fair Value Measurements Recurring [Member]
|
|
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
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| Fair value, available-for-sale securities |
50,409
|
41,741
|
|
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fair Value Measurements Recurring [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair value, available-for-sale securities |
9,695
|
14,372
|
|
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money market funds [Member] | Fair Value Measurements Recurring [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair value, available-for-sale securities |
9,695
|
14,372
|
|
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Government debt securities [Member] | Fair Value Measurements Recurring [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair value, available-for-sale securities |
|
|
|
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate debt securities [Member] | Fair Value Measurements Recurring [Member]
|
|
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair value, available-for-sale securities |
|
|
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Significant Other Observable Inputs (Level 2) [Member] | Fair Value Measurements Recurring [Member]
|
|
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair value, available-for-sale securities |
53,411
|
57,710
|
|
Significant Other Observable Inputs (Level 2) [Member] | Money market funds [Member] | Fair Value Measurements Recurring [Member]
|
|
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
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| Fair value, available-for-sale securities |
|
|
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Significant Other Observable Inputs (Level 2) [Member] | Government debt securities [Member] | Fair Value Measurements Recurring [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair value, available-for-sale securities |
3,002
|
15,969
|
|
Significant Other Observable Inputs (Level 2) [Member] | Corporate debt securities [Member] | Fair Value Measurements Recurring [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair value, available-for-sale securities |
50,409
|
41,741
|
|
Significant Unobservable Inputs (Level 3) [Member] | Fair Value Measurements Recurring [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair value, available-for-sale securities |
|
|
|
Significant Unobservable Inputs (Level 3) [Member] | Money market funds [Member] | Fair Value Measurements Recurring [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair value, available-for-sale securities |
|
|
|
Significant Unobservable Inputs (Level 3) [Member] | Government debt securities [Member] | Fair Value Measurements Recurring [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
|
| Fair value, available-for-sale securities |
|
|
|
Significant Unobservable Inputs (Level 3) [Member] | Corporate debt securities [Member] | Fair Value Measurements Recurring [Member]
|
|
|
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |
|
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| Fair value, available-for-sale securities |
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