Investment Portfolio - Additional Information (Detail) $ in Millions	12 Months Ended
Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Investment [Line Items]
Number of investments in money market securities	1
Maturities of time deposits, description	24 months
Percentage of available-for-sale investments collateralized by US government agency debentures	86.00%	80.00%
Assets, fair value disclosure	$ 40.9	$ 35.4
Available-for-sale securities, amortized cost basis	2.8	3.5
Accumulated other comprehensive income (loss), other than temporary impairment, not credit loss, net of tax, available-for-sale, debt securities	$ 1.2	$ 1.6
Available for sale securities fair value estimates percentage of third party pricing	95.00%	94.00%
Available for sale securities fair value estimates percentage of broker pricing	5.00%	6.00%

Available for Sale Securities Fair Value Estimates Percentage of Broker Pricing

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Available for Sale Securities Fair Value Estimates Percentage of Third Party Pricing

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Line items represent reporting 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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Number of Investments in Money Market Securities

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- Definition

The percentage of available-for-sale investments held by the entity that are collateralized by United States government agency debentures.

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Accumulated other comprehensive loss related to portion of other than temporary impairment (OTTI) due to factors other than credit losses on debt securities categorized as available-for-sale that an entity does not intend to sell and which it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis of the debt security. The amount represented by this item is net of tax, as applicable.

+ References

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Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

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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.

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Description of time deposit maturities, including certificates of deposit.

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