Defined Benefit Pension and Other Postretirement Plans (Tables)

9 Months Ended

Jun. 30, 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 June 30,	2018			2017			2018			2017
Service cost	$	1,882		$	2,023		$	66		$	62
Interest cost	5,766			5,540			111			108
Expected return on assets	(7,776		)	(7,497		)	(178		)	(164		)
Amortization of:
Prior service cost (benefit)	61			81			(110		)	(160		)
Actuarial loss	2,984			3,706			23			28
Net benefit cost (benefit)	2,917			3,853			(88		)	(126		)
Change in associated regulatory liabilities	—			—			(122		)	(123		)
Net benefit cost (benefit) after change in regulatory liabilities	$	2,917		$	3,853		$	(210	)	$	(249	)
	Pension Benefits						Other Postretirement Benefits
Nine Months Ended June 30,	2018			2017			2018			2017
Service cost	$	5,644		$	6,068		$	200		$	184
Interest cost	17,300			16,618			335			323
Expected return on assets	(23,330		)	(22,490		)	(532		)	(492		)
Amortization of:
Prior service cost (benefit)	187			244			(330		)	(480		)
Actuarial loss	8,952			11,119			71			85
Net benefit cost (benefit)	8,753			11,559			(256		)	(380		)
Change in associated regulatory liabilities	—			—			(368		)	(368		)
Net benefit cost (benefit) after change in regulatory liabilities	$	8,753		$	11,559		$	(624	)	$	(748	)