Condensed Consolidated Statements of Comprehensive Income (unaudited) Condensed Consolidated Statements of Comprehensive Income (Parenthetical) (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]
Tax on (loss) gain on derivative instruments	$ 0	$ (2,538)	$ 0	$ (4,337)
Tax on reclassifications of net losses (gains) on derivative instruments	(278)	(84)	(556)	(168)
Tax on benefit plans	$ (67)	$ (139)	$ (137)	$ (278)