Investments in Available-for-Sale Securities (Schedule of Investments) (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost Basis	$ 20,215	$ 97,116
Available-for-sale, Gains		12
Available-for-sale, Losses	(131)	(363)
Available-for-sale, Fair Value	20,084	96,765
U.S. government and agency securities
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost Basis	6,075	57,299
Available-for-sale, Gains		11
Available-for-sale, Losses	(33)	(86)
Available-for-sale, Fair Value	6,042	57,224
Corporate notes and bonds
Debt Securities, Available-for-sale [Line Items]
Available-for-sale, Cost Basis	14,140	39,817
Available-for-sale, Gains		1
Available-for-sale, Losses	(98)	(277)
Available-for-sale, Fair Value	$ 14,042	$ 39,541

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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