CONDENSED CONSOLIDATED STATEMENTS OF PARTNERS' CAPITAL (USD $) In Thousands	Total	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	Limited Partners	Class B Units
Beginning balance at Dec. 31, 2011	$ 2,323,957	$ (127,741)	$ 20,788	$ 2,035,271	$ 395,639
Net income	194,752		3,298	176,640	14,814
Acquisition of additional interest in WesPac Memphis	(17,328)		(2,792)	(14,536)
Credits associated with agreement and plan of merger	422			422
Distributions paid to unitholders	(278,274)		3,837	(282,111)
Net proceeds from issuance of units	246,805			246,805
Amortization of unit-based compensation awards	10,534			10,534
Proceeds from exercise of unit options	1,067			1,067
Payment of tax withholding on issuance of LTIP awards	(1,608)			(1,608)
Distributions paid to noncontrolling interests	(8,900)		(8,900)
Other comprehensive income (loss)	(28,858)	(28,858)
Noncash accrual for distribution equivalent rights	(555)			(555)
Other	659		(29)	688
Ending balance at Sep. 30, 2012	2,442,673	(156,599)	16,202	2,172,617	410,453
Beginning balance at Dec. 31, 2012	2,388,840	(158,779)	16,527	2,117,788	413,304
Net income	246,120		3,095	226,306	16,719
Acquisition of additional interest in WesPac Memphis	(9,727)		(1,495)	(8,232)
Distributions paid to unitholders	(305,544)		2,915	(308,459)
Conversion of Class B Units to LP Units				430,023	(430,023)
Net proceeds from issuance of units	382,319			382,319
Amortization of unit-based compensation awards	12,438			12,438
Proceeds from exercise of unit options	1,201			1,201
Payment of tax withholding on issuance of LTIP awards	(3,741)			(3,741)
Distributions paid to noncontrolling interests	(5,629)		(5,629)
Other comprehensive income (loss)	36,102	36,102
Noncash accrual for distribution equivalent rights	(1,437)			(1,437)
Other	(19)		66	(85)
Ending balance at Sep. 30, 2013	$ 2,740,923	$ (122,677)	$ 15,479	$ 2,848,121