Defined Benefit Pension and Other Postretirement Plans (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Pension Benefits [Member]
Components of net periodic pension expense and other postretirement benefit costs [Abstract]
Service cost	$ 1,623	$ 2,053
Interest cost	5,721	5,196
Expected return on assets	(6,650)	(6,198)
Amortization of:
Prior service cost (benefit)	0	0
Actuarial loss	1,748	3,428
Net benefit cost	2,442	4,479
Change in associated regulatory liabilities	0	0
Net expense	2,442	4,479
Other Postretirement Benefits [Member]
Components of net periodic pension expense and other postretirement benefit costs [Abstract]
Service cost	41	51
Interest cost	127	143
Expected return on assets	(139)	(132)
Amortization of:
Prior service cost (benefit)	(160)	(105)
Actuarial loss	37	91
Net benefit cost	(94)	48
Change in associated regulatory liabilities	918	815
Net expense	$ 824	$ 863