Defined Benefit Pension and Other Postretirement Plans (Tables)

6 Months Ended

Mar. 31, 2018

Defined Benefit Plan [Abstract]

Schedule of Components of Net Periodic Pension Expense and Other Postretirement Benefit Costs

Net periodic pension expense and other postretirement benefit costs include the following components:

	Pension Benefits						Other Postretirement Benefits
Three Months Ended March 31,	2018			2017			2018			2017
Service cost	$	1,881		$	2,022		$	67		$	61
Interest cost	5,767			5,539			112			107
Expected return on assets	(7,777		)	(7,496		)	(177		)	(164		)
Amortization of:
Prior service cost (benefit)	63			82			(110		)	(160		)
Actuarial loss	2,984			3,706			24			29
Net benefit cost (benefit)	2,918			3,853			(84		)	(127		)
Change in associated regulatory liabilities	—			—			(123		)	(123		)
Net benefit cost (benefit) after change in regulatory liabilities	$	2,918		$	3,853		$	(207	)	$	(250	)
	Pension Benefits						Other Postretirement Benefits
Six Months Ended March 31,	2018			2017			2018			2017
Service cost	$	3,762		$	4,045		$	134		$	122
Interest cost	11,534			11,078			224			215
Expected return on assets	(15,554		)	(14,993		)	(354		)	(328		)
Amortization of:
Prior service cost (benefit)	126			163			(220		)	(320		)
Actuarial loss	5,968			7,413			48			57
Net benefit cost (benefit)	5,836			7,706			(168		)	(254		)
Change in associated regulatory liabilities	—			—			(246		)	(245		)
Net benefit cost (benefit) after change in regulatory liabilities	$	5,836		$	7,706		$	(414	)	$	(499	)