Partners' Capital and Partnership Distributions (Details 2) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended												12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Capital Unit [Line Items]
Total amount paid	$ 0.0	$ 19.3	$ 30.6	$ 19.7	$ 0.0	$ 28.5	$ 32.9	$ 30.0	$ 19.7	$ 24.1	$ 27.8	$ 31.4
Per common unit (in dollars per share)	$ 0.00	$ 0.17	$ 0.27	$ 0.27	$ 0.00	$ 0.39	$ 0.45	$ 0.41	$ 0.27	$ 0.33	$ 0.38	$ 0.43
Common units outstanding (in thousands) (in units)	113,283,000	113,283,000	113,283,000	73,128,269	73,123,000	73,123,000	73,123,000	73,123,000	73,117,000	73,114,000	73,113,000	73,113,000	113,282,973	73,128,269	73,123,000
Total amount of cash distributions paid													$ 69.6	$ 91.4	$ 103.1
Per common unit of (in dollars per share)													$ 0.71	$ 1.25	$ 1.41
Affiliates
Capital Unit [Line Items]
Total amount paid	$ 0.0	$ 6.6	$ 10.5	$ 10.5	$ 0.0	$ 15.2	$ 17.5	$ 16.0	$ 10.5	$ 12.8	$ 14.8	$ 16.7
Total amount of cash distributions paid													$ 27.6	$ 48.7	$ 54.9
Public unitholders
Capital Unit [Line Items]
Total amount paid	$ 0.0	$ 12.7	$ 20.1	$ 9.2	$ 0.0	$ 13.3	$ 15.4	$ 14.0	$ 9.2	$ 11.3	$ 13.0	$ 14.7
Total amount of cash distributions paid													$ 42.0	$ 42.7	$ 48.2