Defined Benefit Pension and Other Postretirement Plans (Tables)

6 Months Ended

Mar. 31, 2017

Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [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,	2017			2016			2017			2016
Service cost	$	2,022		$	1,732		$	61		$	45
Interest cost	5,539			5,818			107			117
Expected return on assets	(7,496		)	(7,168		)	(164		)	(149		)
Amortization of:
Prior service cost (benefit)	82			87			(160		)	(160		)
Actuarial loss	3,706			2,393			29			25
Net benefit cost (income)	3,853			2,862			(127		)	(122		)
Change in associated regulatory liabilities	—			—			(123		)	876
Net benefit cost (income) after change in regulatory liabilities	$	3,853		$	2,862		$	(250	)	$	754
	Pension Benefits						Other Postretirement Benefits
Six Months Ended March 31,	2017			2016			2017			2016
Service cost	$	4,045		$	3,464		$	122		$	91
Interest cost	11,078			11,635			215			233
Expected return on assets	(14,993		)	(14,335		)	(328		)	(298		)
Amortization of:
Prior service cost (benefit)	163			174			(320		)	(320		)
Actuarial loss	7,413			4,786			57			49
Net benefit cost (income)	7,706			5,724			(254		)	(245		)
Change in associated regulatory liabilities	—			—			(245		)	1,754
Net benefit cost (income) after change in regulatory liabilities	$	7,706		$	5,724		$	(499	)	$	1,509