Benefit Plans - Changes in Benefit Obligation for Postemployment Benefits (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Change in benefit obligation:
Beginning obligation	$ 137,575	$ 112,751
Service cost	16,399	13,327	11,409
Interest cost	5,639	5,054	4,379
Benefits paid	(51,989)	(42,572)
Actuarial loss	55,025	49,015
Benefit obligation at September 30	$ 162,649	$ 137,575	$ 112,751