Marketable Securities - Available-For-Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Available-For-Sale Securities
Amortized Cost	$ 63,378	$ 71,485
Gross Unrealized Gain	283	277
Gross Unrealized (Losses)	(229)	(255)
Estimated Fair Value	63,432	71,507
Corporate debt securities
Available-For-Sale Securities
Amortized Cost	34,457	42,584
Gross Unrealized Gain	62	165
Gross Unrealized (Losses)	(160)	(40)
Estimated Fair Value	34,359	42,709
Tax-exempt municipal securities
Available-For-Sale Securities
Amortized Cost	23,321	23,301
Gross Unrealized Gain	221	112
Gross Unrealized (Losses)	(69)	(215)
Estimated Fair Value	23,473	23,198
Variable rate demand notes
Available-For-Sale Securities
Amortized Cost	5,600	5,600
Gross Unrealized Gain	0	0
Gross Unrealized (Losses)	0	0
Estimated Fair Value	$ 5,600	$ 5,600

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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+ References

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