Compensation Programs - Schedule of Performance- and Service- Based Stock Award Activity (Detail) (USD $)	3 Months Ended
Mar. 31, 2013
Statement Of Partners Capital [Abstract]
Unvested stock awards outstanding at beginning of period	657,720
Vestings	(143,523)
Forfeitures	(19,969)
Unvested stock awards outstanding at end of period	494,228
Unvested stock awards outstanding at beginning of period	$ 12.48
Vestings	$ 12.17
Forfeitures	$ 12.65
Unvested stock awards outstanding at end of period	$ 12.56

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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- 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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