Leases - Additional Information (Details)	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Operating Leased Assets [Line Items]
Operating leases placed in services dates description	SDTS, SDTS FERC and SPLLC have entered into various leases with Sharyland and SU FERC for all of our placed in service T&D assets. The master lease agreements, as amended, expire at various dates from December 31, 2015 through December 31, 2022.
Maximum [Member]
Operating Leased Assets [Line Items]
Additional rent, percentage	37.00%
Minimum [Member]
Operating Leased Assets [Line Items]
Additional rent, percentage	23.00%
Sharyland
Operating Leased Assets [Line Items]
Percentage of rent recognized	0.00%	0.00%