CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Statement of Comprehensive Income [Abstract]
Net income		$ 180,960	$ 141,970	$ 114,809
Other comprehensive income, net of tax
Unrealized gain (loss) on available for sale securities, net of tax of $(1,135), $426 and $(330), respectively	[1]	1,603	(618)	479
Net unrealized gain (loss) on derivatives, net of tax of $(56), $61 and $23, respectively		93	(105)	(39)
Adjustment to postemployment benefit obligation, net of tax of $3,688, $2,162 and $(5,934), respectively		(5,496)	(3,250)	8,710
Other comprehensive (loss) income		(3,800)	(3,973)	9,150
Comprehensive income		$ 177,160	$ 137,997	$ 123,959

[1] Available for sale securities are included in other noncurrent assets on the Consolidated Balance Sheets.