Incentive Plans - Summary of Activity in Outstanding Grants (Detail)	12 Months Ended
	Dec. 31, 2012
Unit Based Compensation Arrangement [Line Items]
Outstanding grants at the beginning of the period	870,344
Grants during the period	272,150
Grants vested and paid during the period	(189,736)
Forfeitures during the period	(40,444)
Outstanding grants at the end of the period	912,314