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Fair Value Measurements (Details) - Recurring - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018
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U.S. Treasury Notes |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, Fair Value Disclosure | $ 9,225 | $ 8,920
U.S. Treasury Notes | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, Fair Value Disclosure | 9,225 | 8,920
Corporate Notes / Bonds |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, Fair Value Disclosure | 8,169 | 7,934
Corporate Notes / Bonds | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, Fair Value Disclosure | 8,169 | 7,934
Commercial Paper |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, Fair Value Disclosure | 3,482 | 2,952
Commercial Paper | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, Fair Value Disclosure | 3,482 | 2,952
U.S. Treasury Bills |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, Fair Value Disclosure | 2,385 | 2,983
U.S. Treasury Bills | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, Fair Value Disclosure | 2,385 | $ 2,983
U.S. Government Agencies |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, Fair Value Disclosure | 2,249 |
U.S. Government Agencies | Level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Assets, Fair Value Disclosure | $ 2,249 |

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