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Fair Value Measurements (Details) - USD ($) $ in Thousands | 6 Months Ended |
--- | --- | ---
Jun. 30, 2019 | Dec. 31, 2018
Assets and liabilities measured at fair value on a recurring basis |  |
Marketable securities in deferred compensation plan | $ 4,237 | $ 3,868
Fair value measurement on a recurring basis | Deferred compensation plan | Trustees and Management |  |
Assets and liabilities measured at fair value on a recurring basis |  |
Maximum percentage of participants' compensation which is deferrable (as a percent) | 100.00% |
Marketable securities in deferred compensation plan | $ 4,200 |

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