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Fair Value Measurements - Additional Information (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Jun. 30, 2018
Jun. 30, 2017
Jun. 30, 2018
Jun. 30, 2017
Fair Value Disclosures [Abstract]        
Unrealized gain (loss) on available-for-sale marketable securities, net of taxes $ 97 $ 602 $ (1,041) $ 1,081
Proceeds from available for sale municipal bonds 3,300 7,000 5,775 14,681
Losses from the sale of available-for-sale securities $ 100 $ 100 $ 156 $ 200