Short-Term Investments (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 29,826	$ 56,932
Gross Unrealized Gains	4
Gross Unrealized Losses		(3)
Estimated Fair Value	29,830	56,929
Municipal bonds and notes
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		2,986
Gross Unrealized Losses		0
Estimated Fair Value		2,986
Zero coupon bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	26,857	33,919
Gross Unrealized Gains	6
Gross Unrealized Losses		0
Estimated Fair Value	26,863	33,919
Corporate bonds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	2,451	19,509
Gross Unrealized Losses	(2)	(3)
Estimated Fair Value	2,449	19,506
Certificates of deposit
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	518	518
Gross Unrealized Losses	0	0
Estimated Fair Value	$ 518	$ 518

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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-SubTopic 10
-Section 50
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-Subparagraph (b)
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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).

+ References

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-Publisher FASB
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-Publisher FASB
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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), classified as current.

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