Period of cliff vesting for option valuation.

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- Definition

Period of graded vesting for option valuation.

+ References

No definition available.

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Accrued Liabilities

+ References

No definition available.

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- Definition

Share based compensation arrangement by share based payment award fair value assumptions historical volatility rate.

+ References

No definition available.

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- Definition

Share based compensation arrangement by share based payment award fair value assumptions implied volatility rate on publicly traded options.

+ References

No definition available.

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- Definition

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

+ References

No definition available.

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- Definition

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

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- Definition

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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- Definition

Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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- Definition

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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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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-Publisher FASB
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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.

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- Definition

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

+ References

No definition available.

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- Definition

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

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- Definition

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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- Definition

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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- Definition

Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

+ References

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- Definition

Description of terms of award under share-based payment arrangement.

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- Definition

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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- Definition

Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Stock Compensation Plans - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Award vesting terms	vesting terms ranging from three to five years which primarily includes 1) options that vest in one-fifth increments beginning on the grant date and continuing on each of the first four anniversaries of the grant date and 2) options that cliff-vest on the fifth anniversary of the grant date.
Period of graded vesting for option valuation	4 years
Period of cliff vesting for option valuation	5 years
Expected dividend yield	5.00%	5.00%	5.00%
Total unrecognized compensation cost related to nonvested awards	$ 2,544
Weighted average number of years over which compensation cost related to nonvested awards is expected to be recognized	1 year 7 months 13 days
Shares available for future stock option and restricted share grants to employees and directors under existing plans	2,435,451
Aggregate intrinsic value of options outstanding	$ 13,824
Aggregate intrinsic value of options exercisable	11,927
Total intrinsic value of options exercised	1,644
Accrued expenses, liability	$ 11,589	$ 23,297
Common Class A [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected Volatility	90.00%
Volatility rate on publicly traded options	10.00%
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
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%
2019 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional shares reserved	86,093
Performance Based Compensation [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Compensation expense related to performance based compensation agreements	$ 10,484
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