Performance based awards eliminated minimum vesting period.

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- Definition

Share based compensation arrangement by share based payment award award contractual term.

+ References

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- Definition

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

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Aggregate number of common shares reserved for future issuance.

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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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Amount of cost to be recognized for nonvested award under share-based payment arrangement. Excludes share and unit options.

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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

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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- Definition

Date the equity-based award expires, in CCYY-MM-DD format.

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

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

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Equity Incentive Plans - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Securities remaining available for future issuance	5,000,000
Employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options granted (in shares)	0	0
Share-based compensation expenses			$ 0.1
Employee Stock Options \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	1 year
Employee Stock Options \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	4 years
Restricted Stock And Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Performance-based restricted stock and restricted stock units, eliminated minimum vesting period under amended 2004 plan	3 years
Share-based compensation expenses	$ 4.4	$ 5.8	6.0
Total unrecognized compensation expense related to grants of restricted stock and restricted stock units	$ 3.8
Weighted average period for unrecognized compensation expense related to grants of stock options	1 year 8 months 12 days
Shares vested related to grants of restricted stock and restricted stock units	$ 5.0	$ 5.2	$ 6.0
2000 Plan \| Employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Contractual term of stock options	ten years
2000 Plan \| Employee Stock Options \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	4 years
2000 Plan \| Employee Stock Options \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period	5 years
2000 Plan \| Class A common stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares authorized under 2000 plan and 2004 plan	11,500,000
2004 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation award extended expiration date	May 29, 2024
2004 Plan \| Employee Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Contractual term of stock options	ten years
Vesting period	4 years
2004 Plan \| Class A common stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock shares authorized under 2000 plan and 2004 plan	10,000,000