|
Fair Value (Details) (Fair Value, Measurements, Recurring [Member], USD $)
In Thousands, unless otherwise specified |
Jun. 30, 2014
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Dec. 31, 2013
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|---|---|---|
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Fair Value, Inputs, Level 1 [Member]
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| Fair Value | ||
| Investments at fair value | $ 12,482 | $ 9,059 |
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Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
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| Fair Value | ||
| Investments at fair value | 12,482 | 9,059 |
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Fair Value, Inputs, Level 2 [Member]
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| Fair Value | ||
| Investments at fair value | 163,147 | 202,721 |
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Fair Value, Inputs, Level 2 [Member] | US Treasury Securities [Member]
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| Fair Value | ||
| Investments at fair value | 2,049 | 2,085 |
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Fair Value, Inputs, Level 2 [Member] | US Government-sponsored Enterprises Debt Securities [Member]
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| Fair Value | ||
| Investments at fair value | 57,510 | 67,178 |
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Fair Value, Inputs, Level 2 [Member] | Corporate Bond Securities and Commercial Paper [Member]
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| Fair Value | ||
| Investments at fair value | 103,588 | 133,458 |
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Estimate of Fair Value Measurement [Member]
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| Fair Value | ||
| Investments at fair value | 175,629 | 211,780 |
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Estimate of Fair Value Measurement [Member] | Money Market Funds [Member]
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| Fair Value | ||
| Investments at fair value | 12,482 | 9,059 |
|
Estimate of Fair Value Measurement [Member] | US Treasury Securities [Member]
|
||
| Fair Value | ||
| Investments at fair value | 2,049 | 2,085 |
|
Estimate of Fair Value Measurement [Member] | US Government-sponsored Enterprises Debt Securities [Member]
|
||
| Fair Value | ||
| Investments at fair value | 57,510 | 67,178 |
|
Estimate of Fair Value Measurement [Member] | Corporate Bond Securities and Commercial Paper [Member]
|
||
| Fair Value | ||
| Investments at fair value | $ 103,588 | $ 133,458 |