Equity-based Awards, Restricted Unit Awards (Details) - Restricted Common Unit Awards [Member] - USD ($) $ / shares in Units, $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting rate of restricted common unit awards (in hundredths)		25.00%
Summary of awards activity, equity instruments other than options [Roll Forward]
Beginning of period (in units)		1,960,520
Vested (in units)		(1,167,578)
Forfeited (in units)		(9,350)
End of period (in units)		783,592
Restricted units outstanding, weighted-average grant date fair value [Roll Forward]
Weighted-average grant date fair value per unit, at beginning of period (in dollars per unit)	[1]	$ 27.88
Vested weighted-average grant date fair value per unit (in dollars per unit)	[1]	27.39
Forfeited weighted-average grant date fair value per unit (in dollars per unit)	[1]	28.32
Weighted-average grant date fair value per unit, at end of period (in dollars per unit)	[1]	$ 28.60
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]
Cash distributions paid to restricted common unitholders		$ 0.8	$ 1.5
Total intrinsic value of our restricted common unit awards that vested during period		26.8	$ 62.4
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost		$ 4.7
Recognition period for total unrecognized compensation cost (in years)		10 months 24 days
Enterprise [Member]
Unrecognized Compensation Expense [Abstract]
Unrecognized compensation cost		$ 3.5

[1] Determined by dividing the aggregate grant date fair value of awards (before an allowance for forfeitures) by the number of awards issued.