Summary of Unvested Restricted Stock and Share Units Transactions (Detail)	12 Months Ended
Dec. 31, 2017 $ / shares shares
Restricted Stock
Shares
Unvested, beginning balance \| shares	6,495,049
Granted, shares \| shares	3,793,925
Vested, shares \| shares	(2,571,398)
Forfeited, shares \| shares	(357,232)
Unvested, ending balance \| shares	7,360,344
Weighted average grant date fair value
Weighted average grant date fair value, beginning balance \| $ / shares	$ 24.04
Weighted average grant date fair value, granted \| $ / shares	27.54
Weighted average grant date fair value, vested \| $ / shares	22.98
Weighted average grant date fair value, forfeited \| $ / shares	24.77
Weighted average grant date fair value, ending Balance \| $ / shares	$ 26.18
Restricted Stock Units (RSUs)
Shares
Unvested, beginning balance \| shares	1,640,410
Granted, shares \| shares	524,350
Vested, shares \| shares	(211,689)
Forfeited, shares \| shares	(608,011)
Unvested, ending balance \| shares	1,345,060
Weighted average grant date fair value
Weighted average grant date fair value, beginning balance \| $ / shares	$ 29.52
Weighted average grant date fair value, granted \| $ / shares	24.13
Weighted average grant date fair value, vested \| $ / shares	41.12
Weighted average grant date fair value, forfeited \| $ / shares	35.85
Weighted average grant date fair value, ending Balance \| $ / shares	$ 22.73

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)(iv)(3)
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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)(iii)(3)
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- Definition

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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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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).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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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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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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-Name Accounting Standards Codification
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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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