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Fair Value of Financial Instruments -Fair Value Hierarchy (Details) (USD $)
In Thousands, unless otherwise specified
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Sep. 30, 2013
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Dec. 31, 2012
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
$ 95,151 |
$ 94,843 |
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Level 1 | Recurring Basis
|
|
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| Assets, Fair Value Disclosure [Abstract] |
|
|
| Available-for-sale securities, fair value |
0 |
0 |
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Level 2 | Recurring Basis
|
|
|
| Assets, Fair Value Disclosure [Abstract] |
|
|
| Available-for-sale securities, fair value |
95,151 |
94,843 |
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Level 3 | Recurring Basis
|
|
|
| Assets, Fair Value Disclosure [Abstract] |
|
|
| Available-for-sale securities, fair value |
0 |
0 |
|
Fair Value | Recurring Basis
|
|
|
| Assets, Fair Value Disclosure [Abstract] |
|
|
| Available-for-sale securities, fair value |
95,151 |
94,843 |
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Commercial Paper
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
55,571 |
32,376 |
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Commercial Paper | Level 1 | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
0 |
0 |
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Commercial Paper | Level 2 | Recurring Basis
|
|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
55,571 |
32,376 |
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Commercial Paper | Level 3 | Recurring Basis
|
|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
0 |
0 |
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Commercial Paper | Fair Value | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
|
| Available-for-sale securities, fair value |
55,571 |
32,376 |
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US Government Agencies
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
8,715 |
62,467 |
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US Government Agencies | Level 1 | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
|
| Available-for-sale securities, fair value |
0 |
0 |
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US Government Agencies | Level 2 | Recurring Basis
|
|
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| Assets, Fair Value Disclosure [Abstract] |
|
|
| Available-for-sale securities, fair value |
8,715 |
62,467 |
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US Government Agencies | Level 3 | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
0 |
0 |
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US Government Agencies | Fair Value | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
|
| Available-for-sale securities, fair value |
8,715 |
62,467 |
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Municipal bonds
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
1,126 |
|
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Municipal bonds | Level 1 | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
0 |
|
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Municipal bonds | Level 2 | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
1,126 |
|
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Municipal bonds | Level 3 | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
0 |
|
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Municipal bonds | Fair Value | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
1,126 |
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Corporate bonds
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| Assets, Fair Value Disclosure [Abstract] |
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| Available-for-sale securities, fair value |
25,741 |
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Corporate bonds | Level 1 | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
0 |
|
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Corporate bonds | Level 2 | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
|
| Available-for-sale securities, fair value |
25,741 |
|
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Corporate bonds | Level 3 | Recurring Basis
|
|
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| Assets, Fair Value Disclosure [Abstract] |
|
|
| Available-for-sale securities, fair value |
0 |
|
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Corporate bonds | Fair Value | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
25,741 |
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Asset backed securities
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
3,998 |
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Asset backed securities | Level 1 | Recurring Basis
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| Assets, Fair Value Disclosure [Abstract] |
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| Available-for-sale securities, fair value |
0 |
|
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Asset backed securities | Level 2 | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
3,998 |
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Asset backed securities | Level 3 | Recurring Basis
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|
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
0 |
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Asset backed securities | Fair Value | Recurring Basis
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| Assets, Fair Value Disclosure [Abstract] |
|
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| Available-for-sale securities, fair value |
$ 3,998 |
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