Segment Information - Balance Sheet Information by Segment (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Property, plant and equipment, net	$ 10,371,147	$ 9,259,182
Total assets	11,874,437	10,749,596
Operating Segments | Distribution
Segment Reporting Information [Line Items]
Property, plant and equipment, net	7,644,693	6,849,517
Total assets	11,109,128	10,050,164
Operating Segments | Pipeline and Storage
Segment Reporting Information [Line Items]
Property, plant and equipment, net	2,726,454	2,409,665
Total assets	2,963,480	2,621,601
Eliminations | Eliminations
Segment Reporting Information [Line Items]
Property, plant and equipment, net	0	0
Total assets	$ (2,198,171)	$ (1,922,169)