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Fair Value Measurements - Summary of Placement in the Fair Value Hierarchy of Financial Assets that are Measured at Fair Value on a Recurring Basis (Detail) (USD $)
In Thousands, unless otherwise specified |
Sep. 30, 2013
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Dec. 31, 2012
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Dec. 31, 2011
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|---|---|---|---|
| Assets | |||
| Fair value of assets | $ 325,348 | $ 83,376 | $ 39,097 |
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Equity Securities [Member]
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| Assets | |||
| Fair value of assets | 107,567 | 83,116 | 39,097 |
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Certificates of Deposit [Member]
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| Assets | |||
| Fair value of assets | 1,766 | 260 | |
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US Government Debt Securities [Member]
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| Assets | |||
| Fair value of assets | 205,768 | ||
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Commercial Paper [Member]
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| Assets | |||
| Fair value of assets | 10,247 | ||
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Scenario, Previously Reported [Member]
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| Assets | |||
| Fair value of assets | 83,116 | ||
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Quoted Prices in Active Markets (Level 1) [Member]
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| Assets | |||
| Fair value of assets | 75,754 | 72,988 | 39,097 |
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Quoted Prices in Active Markets (Level 1) [Member] | Equity Securities [Member]
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| Assets | |||
| Fair value of assets | 75,754 | 72,988 | 39,097 |
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Quoted Prices in Active Markets (Level 1) [Member] | Certificates of Deposit [Member]
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| Assets | |||
| Fair value of assets | |||
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Quoted Prices in Active Markets (Level 1) [Member] | US Government Debt Securities [Member]
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| Assets | |||
| Fair value of assets | |||
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Quoted Prices in Active Markets (Level 1) [Member] | Commercial Paper [Member]
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| Assets | |||
| Fair value of assets | |||
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Quoted Prices in Active Markets (Level 1) [Member] | Scenario, Previously Reported [Member]
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| Assets | |||
| Fair value of assets | 72,988 | ||
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Significant Other Observable Inputs (Level 2) [Member]
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| Assets | |||
| Fair value of assets | 249,594 | 10,388 | |
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Significant Other Observable Inputs (Level 2) [Member] | Equity Securities [Member]
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|||
| Assets | |||
| Fair value of assets | 31,813 | 10,128 | |
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Significant Other Observable Inputs (Level 2) [Member] | Certificates of Deposit [Member]
|
|||
| Assets | |||
| Fair value of assets | 1,766 | 260 | |
|
Significant Other Observable Inputs (Level 2) [Member] | US Government Debt Securities [Member]
|
|||
| Assets | |||
| Fair value of assets | 205,768 | ||
|
Significant Other Observable Inputs (Level 2) [Member] | Commercial Paper [Member]
|
|||
| Assets | |||
| Fair value of assets | 10,247 | ||
|
Significant Other Observable Inputs (Level 2) [Member] | Scenario, Previously Reported [Member]
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|||
| Assets | |||
| Fair value of assets | 10,128 | ||
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Significant Unobservable Inputs (Level 3) [Member]
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| Assets | |||
| Fair value of assets | |||
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Significant Unobservable Inputs (Level 3) [Member] | Equity Securities [Member]
|
|||
| Assets | |||
| Fair value of assets | |||
|
Significant Unobservable Inputs (Level 3) [Member] | Certificates of Deposit [Member]
|
|||
| Assets | |||
| Fair value of assets | |||
|
Significant Unobservable Inputs (Level 3) [Member] | US Government Debt Securities [Member]
|
|||
| Assets | |||
| Fair value of assets | |||
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Significant Unobservable Inputs (Level 3) [Member] | Commercial Paper [Member]
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| Assets | |||
| Fair value of assets |