Supplemental Guarantor / Non-Guarantor Financial Information Condensed Consolidating Statement of Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Revenues [Abstract]
Affiliates	$ 54,224	$ 37,139	$ 107,017	$ 71,246
Third parties	9,468	13,801	20,190	24,711
Total revenues	63,692	50,940	127,207	95,957
Operating costs and expenses [Abstract]
Operations	17,923	14,366	34,911	27,162
Depreciation and amortization	9,132	7,713	19,396	15,353
General and administrative	2,487	1,573	4,526	2,936
Total operating costs and expenses	29,542	23,652	58,833	45,451
Operating income (loss)	34,150	27,288	68,374	50,506
Equity in earnings of SLC Pipeline	794	467	1,625	1,207
Interest expense	(11,324)	(8,724)	(21,729)	(17,273)
Loss on early extinguishment of debt	(383)	0	(2,979)	0
Other				(12)
Other nonoperating income (expense) and equity earnings	(10,913)	(8,257)	(23,083)	(16,078)
Income before income taxes	23,237	19,031	45,291	34,428
State income tax expense	(75)	(18)	(150)	(246)
Net income	23,162	19,013	45,141	34,182
Other comprehensive income (loss)	(235)	271	685	1,554
Comprehensive Income	22,927	19,284	45,826	35,736
Subsidiaries [Member]
Operating costs and expenses [Abstract]
Equity in earnings of subsidiaries	0	0	0	0
SLC Pipeline [Member]
Operating costs and expenses [Abstract]
Equity in earnings of SLC Pipeline	794	467	1,625	1,207
Parent [Member]
Revenues [Abstract]
Affiliates	0	0	0	0
Third parties	0	0	0	0
Total revenues	0	0	0	0
Operating costs and expenses [Abstract]
Operations	0	0	0	0
Depreciation and amortization	0	0	0	0
General and administrative	484	952	1,926	1,703
Total operating costs and expenses	484	952	1,926	1,703
Operating income (loss)	(484)	(952)	(1,926)	(1,703)
Interest expense	(8,310)	(6,121)	(15,018)	(12,243)
Loss on early extinguishment of debt	(383)		(2,979)
Other				0
Other nonoperating income (expense) and equity earnings	23,646	19,965	47,067	35,885
Income before income taxes	23,162	19,013	45,141	34,182
State income tax expense	0	0	0	0
Net income	23,162	19,013	45,141	34,182
Other comprehensive income (loss)	(235)	271	685	1,554
Comprehensive Income	22,927	19,284	45,826	35,736
Parent [Member] | Subsidiaries [Member]
Operating costs and expenses [Abstract]
Equity in earnings of subsidiaries	32,339	26,086	65,064	48,128
Parent [Member] | SLC Pipeline [Member]
Operating costs and expenses [Abstract]
Equity in earnings of SLC Pipeline	0	0	0	0
Guarantor Subsidiaries [Member]
Revenues [Abstract]
Affiliates	54,224	37,139	107,017	71,246
Third parties	9,468	13,801	20,190	24,711
Total revenues	63,692	50,940	127,207	95,957
Operating costs and expenses [Abstract]
Operations	17,923	14,366	34,911	27,162
Depreciation and amortization	9,132	7,713	19,396	15,353
General and administrative	2,003	621	2,600	1,233
Total operating costs and expenses	29,058	22,700	56,907	43,748
Operating income (loss)	34,634	28,240	70,300	52,209
Interest expense	(3,014)	(2,603)	(6,711)	(5,030)
Loss on early extinguishment of debt	0		0
Other				(12)
Other nonoperating income (expense) and equity earnings	(2,220)	(2,136)	(5,086)	(3,835)
Income before income taxes	32,414	26,104	65,214	48,374
State income tax expense	(75)	(18)	(150)	(246)
Net income	32,339	26,086	65,064	48,128
Other comprehensive income (loss)	0	0	0	0
Comprehensive Income	32,339	26,086	65,064	48,128
Guarantor Subsidiaries [Member] | Subsidiaries [Member]
Operating costs and expenses [Abstract]
Equity in earnings of subsidiaries	0	0	0	0
Guarantor Subsidiaries [Member] | SLC Pipeline [Member]
Operating costs and expenses [Abstract]
Equity in earnings of SLC Pipeline	794	467	1,625	1,207
Eliminations [Member]
Revenues [Abstract]
Affiliates	0	0	0	0
Third parties	0	0	0	0
Total revenues	0	0	0	0
Operating costs and expenses [Abstract]
Operations	0	0	0	0
Depreciation and amortization	0	0	0	0
General and administrative	0	0	0	0
Total operating costs and expenses	0	0	0	0
Operating income (loss)	0	0	0	0
Interest expense	0	0	0	0
Loss on early extinguishment of debt	0		0
Other				0
Other nonoperating income (expense) and equity earnings	(32,339)	(26,086)	(65,064)	(48,128)
Income before income taxes	(32,339)	(26,086)	(65,064)	(48,128)
State income tax expense	0	0	0	0
Net income	(32,339)	(26,086)	(65,064)	(48,128)
Other comprehensive income (loss)	0	0	0	0
Comprehensive Income	(32,339)	(26,086)	(65,064)	(48,128)
Eliminations [Member] | Subsidiaries [Member]
Operating costs and expenses [Abstract]
Equity in earnings of subsidiaries	(32,339)	(26,086)	(65,064)	(48,128)
Eliminations [Member] | SLC Pipeline [Member]
Operating costs and expenses [Abstract]
Equity in earnings of SLC Pipeline	$ 0	$ 0	$ 0	$ 0