CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Thousands		12 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net income		$ 131,672	$ 180,960	$ 141,970
Other comprehensive income, net of tax:
Unrealized (loss) gain on available for sale securities, net of tax of $1,499, $(1,135) and $426, respectively	[1]	(2,187)	1,603	(618)
Net unrealized (loss) gain on derivatives, net of tax of $0, $(56), and $61, respectively		0	93	(105)
Adjustment to postemployment benefit obligation, net of tax of $2,466, $3,688 and $2,162, respectively		(3,574)	(5,496)	(3,250)
Other comprehensive (loss)		(5,761)	(3,800)	(3,973)
Comprehensive income		$ 125,911	$ 177,160	$ 137,997

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