Investments in Available-for-Sale Securities (Schedule of Investments) (Details) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost Basis	$ 67,191	$ 135,687
Available-for-sale, Gains	190	201
Available-for-sale, Losses	(144)	(221)
Available-for-sale, Fair Value	67,237	135,667
Available-for-sale, Short-Term Investments	67,237	135,667
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost Basis	14,030	35,044
Available-for-sale, Gains	24	1
Available-for-sale, Losses		(16)
Available-for-sale, Fair Value	14,054	35,029
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost Basis	53,161	100,643
Available-for-sale, Gains	166	200
Available-for-sale, Losses	(144)	(205)
Available-for-sale, Fair Value	$ 53,183	$ 100,638

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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