Marketable Securities - Summary of Major Security Type Assets Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	$ 4,996	$ 58,639
Gross Unrealized Gains	10	3
Gross Unrealized Losses	0	(12)
Estimated Fair Value	5,006	58,630
Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	4,996	31,977
Gross Unrealized Gains	10	3
Gross Unrealized Losses	0	(7)
Estimated Fair Value	5,006	31,973
Government Treasury Bills
Schedule Of Available For Sale Securities [Line Items]
Amortized Cost	0	26,662
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	(5)
Estimated Fair Value	$ 0	$ 26,657

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).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
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-Section 50
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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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

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Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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