Short-term Investment Securities (Details) - USD ($)	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Short-term investment securities	$ 106,376,000		$ 106,339,000
Unrealized gain, net of deferred taxes	7,000	$ 321,000
Tax effect of the unrealized gain (loss) on short-term investment securities	2,000	94,000
Realized gain (loss) on available-for-sale securities	0	$ 0
Accumulated other comprehensive income (loss)	$ (566,000)		(618,000)
Available-for-sale Securities
Debt Securities, Available-for-sale [Line Items]
Weighted-average fixed rate	0.10%
Accumulated other comprehensive income (loss)	$ 38,000		$ 31,000

Interest Income, Weighted-Average Fixed Rate

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at period end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, unrealized gains and losses on certain investments in debt and equity securities, other than temporary impairment (OTTI) losses related to factors other than credit losses on available-for-sale and held-to-maturity debt securities that an entity does not intend to sell and it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis, as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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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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Amount of realized gain (loss) 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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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.

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