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Invesments (Tables) | 12 Months Ended
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Dec. 31, 2015
Investments |
Schedule of available-for-sale securities |
|  |  |  |  |  |  |  | Gross |  |  |  | Gross |  |  |  |  |
|  |  |  | Amortized |  |  |  | Unrealized |  |  |  | Unrealized |  |  |  | Estimated |
|  |  |  | Cost |  |  |  | Gains |  |  |  | Losses |  |  |  | Fair Value |
|  |  |  | (in thousands) |
December 31, 2015 |  |  |  |  |  |  |  |  |
U.S. treasuries |  | $ | 94,935 |  | $ | 6 |  | $ | (23 | ) | $ | 94,918 |
Government agency securities |  | 12,985 |  | 3 |  | — |  | 12,988 |
Corporate debt |  | 8,144 |  | 1 |  | (1 | ) | 8,144 |
Total available-for-sale securities |  | $ | 116,064 |  | $ | 10 |  | $ | (24 | ) | $ | 116,050 |
December 31, 2014 |  |  |  |  |  |  |  |  |
U.S. treasuries |  | $ | 81,506 |  | $ | 27 |  | $ | (6 | ) | $ | 81,527 |
Corporate debt |  | 39,031 |  | 20 |  | (6 | ) | 39,045 |
Total available-for-sale securities |  | $ | 120,537 |  | $ | 47 |  | $ | (12 | ) | $ | 120,572 |
Schedule of available-for-sale securities in a loss position |
|  |  |  | December 31, 2015 |  |  |  | December 31, 2014 |
|  |  |  |  |  |  |  | Gross |  |  |  |  |  |  |  | Gross |
|  |  |  | Estimated |  |  |  | Unrealized |  |  |  | Estimated |  |  |  | Unrealized |
|  |  |  | Fair Value |  |  |  | Losses |  |  |  | Fair Value |  |  |  | Losses |
|  | (in thousands) |
U.S. treasuries |  | $ | 64,922 |  | $ | (23 | ) | $ | 35,001 |  | $ | (6 | )
Corporate debt |  | 3,353 |  | (1 | ) | 13,069 |  | (6 | )
Total |  | $ | 68,275 |  | $ | (24 | ) | $ | 48,070 |  | $ | (12 | )

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