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STOCKHOLDERS' EQUITY - Summary of Restricted Stock, Restricted Stock Unit and Performance-based Stock Unit Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2018 USD ($) $ / shares shares
Restricted Stock, Restricted Stock Units, and Performance-Based Stock Units
Restricted Stock, Restricted Stock Units, and Performance Stock Units
Outstanding at beginning of period (in shares)	1,091
Granted (in shares)	228
Forfeited (in shares)	(1)
Outstanding at end of period (in shares)	940
Unvested, at end of period (in shares)	1,390
Weighted Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 9.81
Granted (in dollars per share) | $ / shares	24.87
Forfeited (in dollars per share) | $ / shares	19.28
Outstanding at end of period (in dollars per share) | $ / shares	14.62
Unvested at end of period (in dollars per share) | $ / shares	$ 14.79
Weighted Average Remaining Contractual Term (in years) and Aggregate Intrinsic Value
Weighted Average Remaining Contractual Term, Outstanding	1 year 23 days
Weighted Average Remaining Contractual Term, Unvested	1 year 20 days
Aggregate Intrinsic Value, Outstanding at end of period | $	$ 15,452
Aggregate Intrinsic Value, Unvested at end of period | $	$ 22,614
Restricted Stock, Restricted Stock Units, and Performance-Based Stock Units | Class A Common Stock
Restricted Stock, Restricted Stock Units, and Performance Stock Units
Class A Common Stock Vested (in shares)	(378)
Weighted Average Grant Date Fair Value
Class A Common Stock Vested (in dollars per share) | $ / shares	$ 6.91
Performance-Based Stock Units
Weighted Average Remaining Contractual Term (in years) and Aggregate Intrinsic Value
Performance-based stock units, percentage of attainment level	100.00%
Performance-Based Stock Units | Class A Common Stock
Weighted Average Remaining Contractual Term (in years) and Aggregate Intrinsic Value
Number of performance-based stock units (in shares)	450

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Additional shares of Class A Common Stock potentially issuable if maximum attainment levels are met.

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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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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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Percentage of vesting of share-based compensation awards.

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Intrinsic value of equity-based compensation awards outstanding. Excludes stock and unit options.

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