Defined Benefit Pension and Other Postretirement Plans (Tables)

6 Months Ended

Mar. 31, 2016

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,	2016			2015			2016			2015
Service cost	$	1,732		$	1,740		$	45		$	49
Interest cost	5,818			5,628			117			118
Expected return on assets	(7,168		)	(7,225		)	(149		)	(153		)
Amortization of:
Prior service cost (benefit)	87			87			(160		)	(160		)
Actuarial loss	2,393			2,198			25			31
Net benefit cost (income)	2,862			2,428			(122		)	(115		)
Change in associated regulatory liabilities	—			—			876			938
Net benefit cost after change in regulatory liabilities	$	2,862		$	2,428		$	754		$	823
	Pension Benefits						Other Postretirement Benefits
Six Months Ended March 31,	2016			2015			2016			2015
Service cost	$	3,464		$	3,481		$	91		$	97
Interest cost	11,635			11,255			233			237
Expected return on assets	(14,335		)	(14,449		)	(298		)	(306		)
Amortization of:
Prior service cost (benefit)	174			174			(320		)	(320		)
Actuarial loss	4,786			4,396			49			63
Net benefit cost (income)	5,724			4,857			(245		)	(229		)
Change in associated regulatory liabilities	—			—			1,754			1,875
Net benefit cost after change in regulatory liabilities	$	5,724		$	4,857		$	1,509		$	1,646