Period of cliff vesting for option valuation.

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- Definition

Period of graded vesting for option valuation.

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No definition available.

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- Definition

Share Based Compensation Arrangement By Share Based Payment Award Accrued Liabilities

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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 remaining outstanding for issuance when additional shares were reserved for issuance.

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No definition available.

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- Definition

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

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No definition available.

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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- Definition

Unrecognized cost of unvested share-based compensation awards.

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- Definition

Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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- 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 an established share-based compensation plan.

+ References

No definition available.

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- Definition

The maximum number of shares (or other type of equity) originally approved (usually by shareholders and board of directors), net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan. As stock or unit options and equity instruments other than options are awarded to participants, the shares or units remain authorized and become reserved for issuance under outstanding awards (not necessarily vested).

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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.

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- Definition

Description of pertinent provisions of equity-based compensation awards that have actual or potential impact upon the company's financial statements.

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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, 2018	Dec. 31, 2017	Dec. 31, 2016
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	$ 2,837
Weighted average number of years over which compensation cost related to nonvested awards is expected to be recognized	1 year 9 months 7 days
Shares available for future stock option and restricted share grants to employees and directors under existing plans	975,215
Aggregate intrinsic value of options outstanding	$ 16,821
Aggregate intrinsic value of options exercisable	16,143
Total intrinsic value of options exercised	12,378
Accrued expenses, liability	$ 19,211	$ 4,793
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	15,500,000
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	$ 18,929
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
2009 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future stock option and restricted share grants to employees and directors under existing plans	183,244	225,418
Additional shares reserved under 2009 ESPP	83,838
2009 Employee Stock Purchase Plan [Member] \| Common Class A [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance to directors and employees	588,154
Employee stock purchase plan, which available for issuance of common stock	88,154
Additional shares reserved under 2009 ESPP	83,838