Equity-Based Compensation Plans (Summary of Service-Based And Performance-Based Awards) (Details) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Service-Based Awards
Number of Phantom Units
Unvested at December 31, 2016 (in shares) | shares	181,230
Granted (in shares) | shares	102,868
Forfeited (in shares) | shares	(3,402)
Settled (in shares) | shares	(40,859)
Unvested at December 31, 2017 (in shares) | shares	239,837.000
Average Grant Date Fair Value
Unvested at December 31, 2016 (in dollars per share) | $ / shares	$ 40.59
Granted (in dollars per share) | $ / shares	32.27
Forfeited (in dollars per share) | $ / shares	37.22
Settled (in dollars per share) | $ / shares	53.84
Unvested at December 31, 2017 (in dollars per share) | $ / shares	$ 34.81
Total Value (in thousands)
Unvested at December 31, 2016 | $	$ 7,356
Granted | $	3,320
Forfeited | $	(127)
Settled | $	(2,200)
Unvested at December 31, 2017 | $	$ 8,349
Performance-Based Awards
Number of Phantom Units
Unvested at December 31, 2016 (in shares) | shares	483,232
Granted (in shares) | shares	194,346
Forfeited (in shares) | shares	(17,410)
Settled (in shares) | shares	(77,793)
Unvested at December 31, 2017 (in shares) | shares	582,375.000
Average Grant Date Fair Value
Unvested at December 31, 2016 (in dollars per share) | $ / shares	$ 38.82
Granted (in dollars per share) | $ / shares	32.43
Forfeited (in dollars per share) | $ / shares	35.43
Settled (in dollars per share) | $ / shares	54.18
Unvested at December 31, 2017 (in dollars per share) | $ / shares	$ 34.73
Total Value (in thousands)
Unvested at December 31, 2016 | $	$ 18,757
Granted | $	6,303
Forfeited | $	(617)
Settled | $	(4,215)
Unvested at December 31, 2017 | $	$ 20,228