Defined Benefit Pension and Other Postretirement Plans (Tables)

6 Months Ended

Mar. 31, 2013

Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]

Component of net periodic pension expense and other postretirement benefit costs

Net periodic pension expense and other postretirement benefit costs relating to our employees include the following components:

	Pension Benefits						Other Postretirement Benefits
	Three Months Ended						Three Months Ended
	March 31,						March 31,
	2013			2012			2013			2012
Service cost	$	2,053		$	1,756		$	51		43
Interest cost	5,196			5,594			143			166
Expected return on assets	(6,198		)	(5,940		)	(132		)	(127		)
Amortization of:
Prior service cost (benefit)	62			62			(105		)	(106		)
Actuarial loss	3,366			1,963			91			99
Net benefit cost	4,479			3,435			48			75
Change in associated regulatory liabilities	—			—			815			784
Net expense	$	4,479		$	3,435		$	863		$	859
	Pension Benefits						Other Postretirement Benefits
	Six Months Ended						Six Months Ended
	March 31,						March 31,
	2013			2012			2013			2012
Service cost	$	4,105		$	3,512		$	102		$	86
Interest cost	10,391			11,188			286			332
Expected return on assets	(12,396		)	(11,880		)	(264		)	(254		)
Amortization of:
Prior service cost (benefit)	124			124			(210		)	(212		)
Actuarial loss	6,732			3,926			182			198
Net benefit cost	8,956			6,870			96			150
Change in associated regulatory liabilities	—			—			1,630			1,568
Net expense	$	8,956		$	6,870		$	1,726		$	1,718