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
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 - (in dollars)	(207)		(207)
Unit-based compensation expenses	2,294		2,294
Transfer of assets between entities under common control in excess of historical cost	136			136
Partner distributions	(158,226)		(151,579)	(6,647)
Accrued distributions to phantom units	(65)		(65)
Net income	58,227		52,186	4,993		1,048
Contributions from noncontrolling interest	9,834					9,834
Distributions to Series A Preferred Units	(3,891)		(3,826)	(65)
Accretion of Series A Preferred Units	(1,226)		(1,205)	(21)
Net cash flow hedge amounts reclassified to earnings	5,824				5,824
Balance at Jun. 30, 2012	$ 3,740,593		$ 3,367,505	$ 328,272	$ 1,065	$ 43,751
Balance - (in Units) at Jun. 30, 2012		170,113,566