Condensed Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012	Mar. 31, 2011
Net income	$ 47,871	$ 60,163	$ 80,539	$ 101,237
Net gains in fair value of derivative instruments (net of tax $(1,869), $0, $(592) and ($3,007))	2,635	578	834	4,819
Reclassifications of net losses on derivative instruments (net of tax of ($403), ($121), $(524) and $(242))	570	170	740	340
Benefit plans, (net of tax of ($81), $78, $(162) and ($1,461), respectively)	77	(110)	216	2,061
Comprehensive income	$ 51,153	$ 60,801	$ 82,329	$ 108,457