LTIP Activity (Detail) (Long Term Incentive Plans, USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Long Term Incentive Plans
Number of LP Units
Beginning Balance	364,913		140,095
Granted	251,184		259,336
Vested	(17,553)		(18,642)
Forfeited	(13,227)		(15,876)
Ending Balance	585,317		364,913
Weighted Average Grant Date Fair Value per LP Unit
Beginning Balance	$ 51.11	[1]	$ 39.81	[1]
Granted	$ 64.88	[1]	$ 56.26	[1]
Vested	$ 55.53	[1]	$ 39.20	[1]
Forfeited	$ 57.03	[1]	$ 49.50	[1]
Ending Balance	$ 56.75	[1]	$ 51.11	[1]
Total Value
Beginning Balance	$ 18,650		$ 5,577
Granted	16,296		14,590
Vested	(975)		(731)
Forfeited	(754)		(786)
Ending Balance	$ 33,217		$ 18,650

[1] Determined by dividing the aggregate grant date fair value of awards by the number of awards issued. The weighted-average grant date fair value per LP Unit for forfeited and vested awards is determined before an allowance for forfeitures.