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Short-term and Long-term Investments - Summary of Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Short-term Investments (Detail) (USD $)
In Thousands, unless otherwise specified |
Sep. 30, 2013
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|---|---|
| Schedule of Available-for-sale Securities [Line Items] | |
| Amortized Cost | $ 217,757 |
| Gross Unrealized Gains | 33 |
| Gross Unrealized Losses | (9) |
| Aggregate Fair Value | 217,781 |
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U.S. Government Debt Securities [Member]
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| Schedule of Available-for-sale Securities [Line Items] | |
| Amortized Cost | 205,747 |
| Gross Unrealized Gains | 27 |
| Gross Unrealized Losses | (6) |
| Aggregate Fair Value | 205,768 |
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Commercial Paper [Member]
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| Schedule of Available-for-sale Securities [Line Items] | |
| Amortized Cost | 10,242 |
| Gross Unrealized Gains | 6 |
| Gross Unrealized Losses | (1) |
| Aggregate Fair Value | 10,247 |
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Certificates of Deposit [Member]
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| Schedule of Available-for-sale Securities [Line Items] | |
| Amortized Cost | 1,768 |
| Gross Unrealized Gains | |
| Gross Unrealized Losses | (2) |
| Aggregate Fair Value | $ 1,766 |