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Marketable Securities (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 81,750,000
Gross Unrealized Gains	6,000
Gross Unrealized Losses	(6,000)
Fair Value	81,750,000
Other-than-temporary unrealized losses	0	$ 0
U.S. Treasury securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	0
Gross Unrealized Gains	0
Gross Unrealized Losses	0
Fair Value	0
Government-sponsored enterprises
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	17,389,000
Gross Unrealized Gains	1,000
Gross Unrealized Losses	0
Fair Value	17,390,000
Corporate debt securities
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	64,361,000	12,738,000
Gross Unrealized Gains	5,000	0
Gross Unrealized Losses	(6,000)	(3,000)
Fair Value	$ 64,360,000	$ 12,735,000

X

- Definition

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).

+ References

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-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
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- Definition

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).

+ References

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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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Amount 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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The amount by which the fair value of an investment in debt and equity securities categorized as Available-for-sale is less than the amortized cost basis or carrying amount of that investment at the balance sheet date and the decline in fair value is deemed to be other than temporary, before considering whether or not such amount is recognized in earnings or other comprehensive income.

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