Investments in Available-for-Sale Securities (Schedule of Investments) (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost Basis	$ 97,116	$ 135,687
Available-for-sale, Gains	12	201
Available-for-sale, Losses	(363)	(221)
Available-for-sale, Fair Value	96,765	135,667
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost Basis	57,299	35,044
Available-for-sale, Gains	11	1
Available-for-sale, Losses	(86)	(16)
Available-for-sale, Fair Value	57,224	35,029
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost Basis	39,817	100,643
Available-for-sale, Gains	1	200
Available-for-sale, Losses	(277)	(205)
Available-for-sale, Fair Value	$ 39,541	$ 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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