Fair Value Measurements - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Unrealized (loss) gain on available-for-sale marketable securities, net of taxes	$ (508)	$ 82	$ (1,549)	$ 1,163
Proceeds from available for sale municipal bonds	2,900	5,700	8,706	20,354
Gains (losses) from the sale of available-for-sale securities	$ (100)	$ 200	$ (200)	$ (100)

Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://www.xbrl.org/2003/role/recommendedDisclosureRef
-Publisher FASB
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Amount after tax, before reclassification adjustments, of unrealized holding gain (loss) on available-for-sale securities.

+ References

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-Publisher FASB
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Amount of cash inflow from sale of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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-Section 45
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