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Marketable Securities - Available-for-sale Securities by Major Security Type (Details) - USD ($) $ in Thousands | Sep. 30, 2021 | Dec. 31, 2020
--- | --- | ---
Marketable Securities [Line Items] |  |
Amortized cost | $ 1,408 | $ 2,848
Gross unrealized holding gains | (12) | (31)
Gross unrealized holding losses |  |
Estimated fair value | 1,420 | 2,879
Corporate bonds and notes [Member] |  |
Marketable Securities [Line Items] |  |
Amortized cost | 808 | 1,312
Gross unrealized holding gains | (11) | (26)
Gross unrealized holding losses |  |
Estimated fair value | 819 | 1,338
Municipal bonds [Member] |  |
Marketable Securities [Line Items] |  |
Amortized cost | 600 | 1,536
Gross unrealized holding gains | (1) | (5)
Gross unrealized holding losses |  |
Estimated fair value | $ 601 | $ 1,541

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- Definition Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading. + References No definition available. + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References 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) -URI http://asc.fasb.org/extlink&oid=123581744&loc=d3e27161-111563 + Details
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- Definition Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale. + References No definition available. + Details
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- Definition This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any. + References No definition available. + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Details
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- Details
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