Marketable Securities - Schedule of Marketable Securities by Category (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 67,653	$ 62,681
Gross Unrealized Holding Gains	239	43
Gross Unrealized Holding Losses		40
Fair Value	67,892	62,684
Municipal Notes and Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	67,653	62,681
Gross Unrealized Holding Gains	239	43
Gross Unrealized Holding Losses		40
Fair Value	$ 67,892	$ 62,684

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on 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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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on 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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Amortized cost 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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Amount 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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