Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions			3 Months Ended								12 Months Ended			14 Months Ended
	Feb. 15, 2017	Feb. 14, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015
Subsequent Event [Line Items]
Distributions per Limited Partner unit (in dollars per share)			$ 0.277000	$ 0.26375	$ 0.25000	$ 0.23500	$ 0.2200	$ 0.2050	$ 0.1900	$ 0.1750	$ 1.02575	$ 0.7900	$ 0.1042	$ 0.1042
Distributions declared and/or paid			$ 58.6	$ 53.9	$ 49.0	$ 41.7	$ 35.3	$ 30.3	$ 27.7	$ 24.1				$ 14.4
General Partner
Subsequent Event [Line Items]
Distributions declared and/or paid			1.2	1.1	1.0	0.9	0.7	0.6	0.5	0.5				0.3
General Public | Common Units
Subsequent Event [Line Items]
Distributions declared and/or paid			24.5	23.3	22.0	17.9	13.9	11.0	10.2	8.0				4.8
SPLC
Subsequent Event [Line Items]
Distributions declared and/or paid			18.7	17.8	16.9	15.8	14.8	13.9	12.8	11.8				7.1
SPLC | Common Units
Subsequent Event [Line Items]
Distributions declared and/or paid			5.9	5.7	5.4	5.1	4.7	4.4	4.1	3.8				2.2
General Partner Incentive | General Partner
Subsequent Event [Line Items]
Distributions declared and/or paid			$ 8.3	$ 6.0	$ 3.7	$ 2.0	$ 1.2	$ 0.4	$ 0.1	$ 0.0				$ 0.0
Subsequent Event
Subsequent Event [Line Items]
Distributions per Limited Partner unit (in dollars per share)		$ 0.277000
Distributions declared and/or paid		$ 58.6
Subsequent Event | General Partner
Subsequent Event [Line Items]
Distributions declared and/or paid		1.2
Subsequent Event | General Public | Common Units
Subsequent Event [Line Items]
Distributions declared and/or paid		24.5
Subsequent Event | SPLC | Common Units
Subsequent Event [Line Items]
Distributions declared and/or paid		24.6
Subsequent Event | General Partner Incentive | General Partner
Subsequent Event [Line Items]
Distributions declared and/or paid		$ 8.3
Subsequent Event | Common units
Subsequent Event [Line Items]
Shares converted (in shares)	67,475,068