Unit-Based Compensation (Phantom Common Unit Awards) (Details) - $ / shares	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2019
Nonvested, Weighted Average Grant Date Fair Value [Roll Forward]
Beginning balance (in dollars per unit)	$ 29.21	$ 29.15
Granted (in dollars per unit)	29.77	30.70
Vested (in dollars per unit)	30.67	30.04
Forfeited (in dollars per unit)	29.13	28.16
Ending balance (in dollars per unit)	$ 29.10	$ 29.21
Phantom common units [Member]
Nonvested, Number of Shares [Roll Forward]
Beginning balance (in units)	2,113,322	2,124,012
Granted (in units)	17,235	655,630
Vested (in units)	155,655	477,256
Forfeited (in units)	122,706	189,064
Ending balance (in units)	1,852,196	2,113,322