Quarterly Financial Data (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	1 Months Ended	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011		Dec. 31, 2010
Quarterly Financial Data [Abstract]
Cash distribution per unit applicable to limited partners	$ 0	$ 0.470	$ 0.462	$ 0.455	$ 0.448		$ 0	$ 0	$ 0	$ 1.835	$ 1.740		$ 1.660
Net Income (Loss) Per Outstanding Limited Partnership Unit Basic and Diluted	$ 0	$ 0.37	$ 0.32	$ 0.30	$ 0.30		$ 0	$ 0	$ 0	$ 1.29	$ 1.38	[1]	$ 1.00	[1]
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	$ 27,560	$ 28,932	$ 23,909	$ 19,204	$ 19,431		$ 12,431	$ 18,391	$ 14,441	$ 91,476	$ 72,823	[1]	$ 56,525	[1]
Operating Income (Loss)	36,705	40,973	35,572	30,116	31,602		20,598	26,648	22,262	138,263	106,213	[1]	88,109	[1]
Total revenues	69,087	81,431	74,054	68,660	68,415		49,151	50,908	45,122	292,560	214,268	[1]	182,137	[1]
Net Income (Loss) Attributable to Parent	30,894	27,039	23,336	22,003	21,774		15,632	18,673	14,600	94,152	79,799	[1]	56,323	[1]
Correction of Error to Net Income	48		(1,157)	(1,159)	(205)		(1,112)	(339)	(569)		(1,972)
Correction of error - limited partners per unit interest			$ (0.02)	$ (0.02)		$ 0.00	$ (0.03)	$ 0.00	$ (0.01)		$ (0.04)		$ (0.06)
Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest	$ 27,495	$ 28,848	$ 23,773	$ 19,128	$ 19,356		$ 12,508	$ 18,373	$ 14,213	$ 91,105	$ 72,589	[1]	$ 56,229	[1]

[1] (1) Restated as described in Note 2.