Defined Benefit Pension and Other Postretirement Plans (Tables)

9 Months Ended

Jun. 30, 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 June 30,	2016			2015			2016			2015
Service cost	$	1,731		$	1,741		$	46		$	48
Interest cost	5,818			5,628			116			119
Expected return on assets	(7,167		)	(7,225		)	(149		)	(153		)
Amortization of:
Prior service cost (benefit)	87			87			(160		)	(160		)
Actuarial loss	2,393			2,199			24			32
Net benefit cost (income)	2,862			2,430			(123		)	(114		)
Change in associated regulatory liabilities	—			—			878			938
Net benefit cost after change in regulatory liabilities	$	2,862		$	2,430		$	755		$	824
	Pension Benefits						Other Postretirement Benefits
Nine Months Ended June 30,	2016			2015			2016			2015
Service cost	$	5,195		$	5,222		$	137		$	145
Interest cost	17,453			16,883			349			356
Expected return on assets	(21,502		)	(21,674		)	(447		)	(459		)
Amortization of:
Prior service cost (benefit)	261			261			(480		)	(480		)
Actuarial loss	7,179			6,595			73			95
Net benefit cost (income)	8,586			7,287			(368		)	(343		)
Change in associated regulatory liabilities	—			—			2,632			2,813
Net benefit cost after change in regulatory liabilities	$	8,586		$	7,287		$	2,264		$	2,470