Unit-Based Compensation Arrangements - Summary of Activity for the Restricted Units Plans (Details) - Restricted Stock Units (RSUs) [Member]	6 Months Ended
	Mar. 31, 2018 $ / shares shares
Restricted Units [Rollforward]
Outstanding, beginning of period (in units) | shares	621,045
Awarded (in units) | shares	424,431
Forfeited (in units) | shares	(12,659)
Vested (with Common Units issued) (in units) | shares	(333,346)
Outstanding, end of period (in units) | shares	699,471
Weighted Average Grant Date Fair Value Per Unit [Abstract]
Outstanding, beginning of period (in dollars per unit) | $ / shares	$ 22.10
Awarded (in dollars per unit) | $ / shares	19.52
Forfeited (in dollars per unit) | $ / shares	(19.73)
Vested (with Common Units issued) (in dollars per unit) | $ / shares	(24.41)
Outstanding, end of period (in dollars per unit) | $ / shares	$ 19.48