Investments - Value of Marketable Investments (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Debt securities: corporate bonds
Cost	$ 700
Gross Unrealized Gains	6
Gross Unrealized Losses	(22)
Carrying Value	684
Marketable equity securities
Cost	513
Gross Unrealized Gains	710
Gross Unrealized Losses	(5)
Carrying Value	1,218
Total
Cost	1,213
Gross Unrealized Gains	716
Gross Unrealized Losses	(27)
Carrying Value	$ 1,902

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Available-For-Sale Equity Securities [Abstract]

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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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-Publisher FASB
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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in equity securities classified as available-for-sale.

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in equity securities classified as 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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