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Financial Instruments - Financial Instruments Measured on Recurring Basis (Detail) (USD $)
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Sep. 30, 2013
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Dec. 31, 2012
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | $ 60,189,000 | $ 60,089,000 |
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Money market funds [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 3,670,000 | 4,643,000 |
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Fair Value Measurements Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 60,189,000 | 60,089,000 |
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Fair Value Measurements Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | US Government Agencies Debt Securities [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 19,780,000 | 6,003,000 |
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Fair Value Measurements Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Corporate debt securities [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 36,739,000 | 49,443,000 |
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Fair Value Measurements Recurring [Member] | Estimate of Fair Value, Fair Value Disclosure [Member] | Money market funds [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 3,670,000 | 4,643,000 |
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Fair Value Measurements Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 3,670,000 | 4,643,000 |
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Fair Value Measurements Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | US Government Agencies Debt Securities [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 0 | 0 |
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Fair Value Measurements Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Corporate debt securities [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 0 | 0 |
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Fair Value Measurements Recurring [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Money market funds [Member]
|
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 3,670,000 | 4,643,000 |
|
Fair Value Measurements Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 56,519,000 | 55,446,000 |
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Fair Value Measurements Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | US Government Agencies Debt Securities [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 19,780,000 | 6,003,000 |
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Fair Value Measurements Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Corporate debt securities [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 36,739,000 | 49,443,000 |
|
Fair Value Measurements Recurring [Member] | Significant Other Observable Inputs (Level 2) [Member] | Money market funds [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 0 | 0 |
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Fair Value Measurements Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member]
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 0 | 0 |
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Fair Value Measurements Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | US Government Agencies Debt Securities [Member]
|
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 0 | 0 |
|
Fair Value Measurements Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Corporate debt securities [Member]
|
||
| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | 0 | 0 |
|
Fair Value Measurements Recurring [Member] | Significant Unobservable Inputs (Level 3) [Member] | Money market funds [Member]
|
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| Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ||
| Fair value, available-for-sale securities | $ 0 | $ 0 |