Cash Equivalents and Investments (Schedule of Estimated Fair Value of Available-for-Sale Securities) (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Schedule of Available-for-sale Securities [Line Items]
Estimated Market Value	$ 18,389	$ 18,393
Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Due within one year	693
Amortized Cost, Due after one year through five years	6,169
Amortized Cost	6,862
Estimated Market Value, Due within one year	693
Estimated Market Value, Due after one year through five years	6,166
Estimated Market Value	$ 6,859	$ 8,969

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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