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Activity Under Equity Incentive Plans Related to RSUs (Detail) - 2008 Equity Incentive Plan - Restricted Stock Units shares in Thousands	6 Months Ended
	Jun. 30, 2018 $ / shares shares
Activity under the Company's equity incentive plans related to restricted stock units
Number of Restricted Stock Units Outstanding, Beginning Balance | shares	1,256
Granted, Number of Restricted Stock Units Outstanding | shares	1,369	[1]
Vested, Number of Restricted Stock Units Outstanding | shares	(502)
Forfeited, Number of Restricted Stock Units Outstanding | shares	(121)
Number of Restricted Stock Units Outstanding, Ending Balance | shares	2,002
Weighted Average Exercise Price per Share
Weighted Average Exercise Price per Share, Beginning Balance | $ / shares	$ 4.53
Granted, Weighted Average Exercise Price per Share | $ / shares	4.42	[1]
Vested, Weighted Average Exercise Price per Share | $ / shares	4.37
Forfeited, Weighted Average Exercise Price per Share | $ / shares	4.17
Weighted Average Exercise Price per Share, Ending Balance | $ / shares	$ 4.51
[1] Includes the number of shares issuable under the performance-based restricted stock unit awards granted during the six months ended June 30, 2018.

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- Definition

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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