Condensed Consolidated Statement of Partners' Capital and Noncontrolling Interest (USD $) In Thousands, except Share data	Total USD ($)	Common Stock [Member]	Common Units [Member] USD ($)	General Partner Interest [Member] USD ($)	Accumulated Other Comprehensive Income (Loss) [Member] USD ($)	Noncontrolling Interest [Member] USD ($)
Balance at Dec. 31, 2011	$ 3,531,076		$ 3,173,090	$ 329,876	$ (4,759)	$ 32,869
Balance - (in Units) at Dec. 31, 2011		157,437,608
Common unit offering, net of costs - (in Units)		12,650,000
Common unit offering, net of costs	296,817		296,817
Common units issued under equity distribution program, units		691,129
Common units issued under equity distribution agreement	15,352
Issuance of common units under LTIP, net of forfeitures and tax withholding - (in Units)		25,958
Issuance of common units under LTIP, net of forfeitures and tax withholdings	(207)		(207)
Unit-based compensation expenses	3,470		3,470
Transfer of assets between entities under common control in excess of historical cost	436			436
Partner distributions	(240,304)		(230,262)	(10,042)
Accrued distributions to phantom units	(86)		(86)
Net income	56,773		48,334	7,012		1,427
Contributions from noncontrolling interest	23,836					23,836
Distributions to Series A Preferred Units	(5,836)		(5,738)	(98)
Accretion of Series A Preferred Units	(1,405)		(1,381)	(24)
Net cash flow hedge amounts reclassified to earnings	6,089				6,089
Balance at Sep. 30, 2012	$ 3,686,011		$ 3,299,389	$ 327,160	$ 1,330	$ 58,132
Balance - (in Units) at Sep. 30, 2012		170,804,695