Marketable Securities - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Gross realized gains from sale or maturity of marketable securities	$ 3,000		$ 0
Gross interest income on securities	377,000	$ 499,000
Accretion income on securities	$ 453,000	432,000
Amortization expense on securities		$ 36,000

Gross interest income on securities.

No definition available.

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- Definition

Amount of accretion of purchase discount on nonoperating securities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.8)
-URI http://asc.fasb.org/extlink&oid=116634182&loc=SL114868664-224227

+ Details

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- Definition

Amount of amortization of purchase premium on nonoperating securities.

+ References

+ Details

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- References

No definition available.

+ Details

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- Definition

Amount of realized gain (loss) on investment in marketable security, including other-than-temporary impairment (OTTI).

+ References

No definition available.

+ Details

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