Consolidated Statements of Comprehensive Income (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net income	$ 124,106	$ 102,098	$ 87,898
Net gains (losses) on derivative instruments (net of tax of $0, $(10,746) and $4,783, respectively)	0	15,153	(6,744)
Reclassifications of net losses on derivative instruments	1,567	471	1,111
Benefit plans (net of tax of $1,002, $(3,325) and $1,948, respectively)	(1,413)	4,689	(2,745)
Reclassifications of benefit plans actuarial losses and prior service costs to net income (net of tax of $(274), $(555) and $(333), respectively)	385	784	394
Other comprehensive income (loss)	539	21,097	(7,984)
Comprehensive income	$ 124,645	$ 123,195	$ 79,914