Defined Benefit Pension and Other Postretirement Plans (Tables)

9 Months Ended

Jun. 30, 2017

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 June 30,	2017			2016			2017			2016
Service cost	$	2,023		$	1,731		$	62		$	46
Interest cost	5,540			5,818			108			116
Expected return on assets	(7,497		)	(7,167		)	(164		)	(149		)
Amortization of:
Prior service cost (benefit)	81			87			(160		)	(160		)
Actuarial loss	3,706			2,393			28			24
Net benefit cost (income)	3,853			2,862			(126		)	(123		)
Change in associated regulatory liabilities	—			—			(123		)	878
Net benefit cost (income) after change in regulatory liabilities	$	3,853		$	2,862		$	(249	)	$	755
	Pension Benefits						Other Postretirement Benefits
Nine Months Ended June 30,	2017			2016			2017			2016
Service cost	$	6,068		$	5,195		$	184		$	137
Interest cost	16,618			17,453			323			349
Expected return on assets	(22,490		)	(21,502		)	(492		)	(447		)
Amortization of:
Prior service cost (benefit)	244			261			(480		)	(480		)
Actuarial loss	11,119			7,179			85			73
Net benefit cost (income)	11,559			8,586			(380		)	(368		)
Change in associated regulatory liabilities	—			—			(368		)	2,632
Net benefit cost (income) after change in regulatory liabilities	$	11,559		$	8,586		$	(748	)	$	2,264