Stock Based Compensation - Summary of Changes in Non Vested Shares of Restricted Stock Outstanding (Detail)	6 Months Ended
Jun. 30, 2018 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Non-vested shares, beginning balance \| shares	4,026,110
Granted (unaudited), shares \| shares	1,277,491
Vested shares \| shares	(1,041,748)
Forfeited (unaudited), shares \| shares	(178,957)
Non-vested shares, ending balance \| shares	4,082,896
Non-vested, weighted average grant-date fair value, beginning of period \| $ / shares	$ 35.63
Granted, weighted average grant-date fair value \| $ / shares	52.47
Vested, weighted average grant-date fair value \| $ / shares	47.10
Forfeited, weighted average grant-date fair value \| $ / shares	37.27
Non-vested, weighted average grant-date fair value, end of period \| $ / shares	$ 37.90

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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-SubTopic 10
-Section 50
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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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- Definition

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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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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No definition available.

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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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- Definition

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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Number of shares related to Restricted Stock Award forfeited during the period.

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Total number of shares issued during the period, including shares forfeited, as a result of Restricted Stock Awards.

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