Stock-Based Compensation - Additional Information (Detail) $ in Thousands	3 Months Ended
Mar. 31, 2021 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for grant (in shares)	2,333,620
Common Class A [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted	18,000
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	5 years
2019 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares reserved (in shares)	86,490
1996 Equity Incentive Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance to directors and employees	17,500,000
1996 Equity Incentive Plan [Member] \| Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of awards of target number of share	0.00%
1996 Equity Incentive Plan [Member] \| Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Range of awards of target number of share	100.00%
Performance Based Compensation [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense related to performance based compensation agreements \| $	$ 2,452
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration date of options granted under equity incentive plan	10 years
Restricted Stock [Member] \| Non-employee Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation expense related to performance based compensation agreements \| $	$ 66
Restricted Stock [Member] \| Percentage of awards vesting on grant date [Member] \| Non-employee Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of awards vesting on grant date	50.00%
Restricted Stock [Member] \| Percentage of Awards Vesting On Last Day of Each Directors Term [Member] \| Non-employee Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	1 year
Percentage of awards vesting on grant date	50.00%

Shares subject to awards as percentage of target number of shares.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Number of additional shares authorized for issuance under share-based payment arrangement.

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Number of shares authorized for issuance under share-based payment arrangement.

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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Net number of share options (or share units) granted during the period.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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