Consolidated Statements of Comprehensive Income Statement (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Statement of Comprehensive Income [Abstract]
Net income	$ 311,183	$ 277,314	$ 275,186
Foreign currency translation adjustment	(1,997)	(2,407)	295
Unrealized (losses) gains on securities, net of taxes of $101, $692, and $(1,350) for the years ended September 30, 2014, 2013, and 2012, respectively	(26)	(952)	2,397
Reclassification adjustment for realized gains included in net income, net of taxes of $86, $133, and $58 for the years ended September 30, 2014, 2013, and 2012, respectively	(147)	(226)	(99)
Net change in unrealized (losses) gains on available-for-sale securities, net of tax	(173)	(1,178)	2,298
Total other comprehensive (loss) income	(2,170)	(3,585)	2,593
Comprehensive income	$ 309,013	$ 273,729	$ 277,779