STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Statement of Comprehensive Income [Abstract]
Net Income	$ 44,232	$ 29,775	$ 79,525	$ 55,517
Net gains (losses) on cash flow hedging derivative instruments:
Net hedging gain arising during the period	57	147	66	203
Reclassification adjustment for (gains) losses included in net income	(55)	(38)	(113)	(85)
Net unrealized (loss) gains on cash flow hedging derivative instruments	2	109	(47)	118
Defined benefit pension and other postretirement benefit plans:
Amortization of actuarial loss included in net periodic pension and postretirement benefit cost	97	90	195	181
Other Comprehensive (Loss) Income, Before Tax	99	199	148	299
Income Tax (Benefit) Expense Related to Items of Other Comprehensive Income	41	76	77	124
Other Comprehensive (Loss) Income, Net of Tax	59	123	71	175
Comprehensive Income	$ 44,291	$ 29,898	$ 79,596	$ 55,692