NET INCOME PER COMMON UNIT (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended						1 Months Ended			12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009		Feb. 29, 2012 General Partner	May 31, 2011 General Partner	Nov. 30, 2009 General Partner	Dec. 31, 2011 General Partner
Common units and interest in the partnership
Additional percentage investment held by General Partner (as a percent)															2.00%	2.00%	2.00%	2.00%
Net income	$ 38.3	$ 40.7	$ 36.1	$ 42.3	$ 37.1	$ 38.6	$ 27.7	$ 33.7	$ 157.4	[1],[2]	$ 137.1	[1]	$ 106.1	[1],[3]
North Baja's contribution prior to acquisition													(8.3)
Net income allocated to partners									157.4		137.1		97.8
Net income allocated to General Partner:
General partner interest excluding Incentive distribution income									(3.1)		(2.7)		(1.9)
Incentive distribution income allocation													(5.3)
General partner interest									(3.1)		(2.7)		(7.2)
Net income allocable to common units									$ 154.3		$ 134.4		$ 90.6
Weighted average common units outstanding									51.1		46.2		38.7
Net income per common unit (in dollars per unit)	$ 0.70	$ 0.75	$ 0.69	$ 0.90	$ 0.79	$ 0.82	$ 0.59	$ 0.71	$ 3.02		$ 2.91		$ 2.34

[1] Recast as discussed in Notes 2 and 5 and includes equity earnings from GTN and Bison from May 3, 2011, date of acquisition, to December 31, 2011.

[2] Includes equity earnings from GTN and Bison from May 3, 2011, date of acquisition, to December 31, 2011.

[3] Recast as discussed in Notes 2 and 5.