Nonvested Performance Share Unit Awards (Detail) (Performance Share Units, USD $)	3 Months Ended
Mar. 31, 2013
Performance Share Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Nonvested at beginning of period, Shares	468,000
Granted, Shares	485,000
Nonvested at end of period, Shares	953,000
Nonvested at beginning of period, Weighted-Average Grant Date Fair Value	$ 12.84
Granted, Weighted-Average Grant Date Fair Value	$ 8.85
Nonvested at end of period, Weighted-Average Grant Date Fair Value	$ 10.81

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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- Definition

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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