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Marketable Securities (Details) - USD ($) $ in Thousands | Jun. 30, 2017 | Dec. 31, 2016
--- | --- | ---
Amortized Cost |  |
Amortized cost | $ 87,841 | $ 147,370
Gross Unrealized Gains |  |
Gross Unrealized Gains | 9 | 13
Gross Unrealized Losses |  |
Gross Unrealized Losses | (28) | (68)
Fair Value |  |
Fair Value | 87,822 | 147,315
Marketable securities considered to be other-than-temporarily impaired | 0 |
Accrued interest included in marketable securities | 400 | 600
U.S. government and municipal obligations |  |
Amortized Cost |  |
Maturing in one year or less | 18,253 | 52,754
Maturing after one year through three years |  | 296
Amortized cost | 18,253 | 53,050
Gross Unrealized Gains |  |
Maturing in one year or less | 7 | 5
Maturing after one year through three years |  | 8
Gross Unrealized Gains | 7 | 13
Gross Unrealized Losses |  |
Maturing in one year or less | (6) | (12)
Gross Unrealized Losses | (6) | (12)
Fair Value |  |
Maturing in one year or less | 18,254 | 52,747
Maturing after one year through three years |  | 304
Fair Value | 18,254 | 53,051
Corporate debt securities |  |
Amortized Cost |  |
Maturing in one year or less | 69,588 | 94,320
Amortized cost | 69,588 | 94,320
Gross Unrealized Gains |  |
Maturing in one year or less | 2 |
Gross Unrealized Gains | 2 |
Gross Unrealized Losses |  |
Maturing in one year or less | (22) | (56)
Gross Unrealized Losses | (22) | (56)
Fair Value |  |
Maturing in one year or less | 69,568 | 94,264
Fair Value | $ 69,568 | $ 94,264

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