Comprehensive Income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Sep. 30, 2011
Comprehensive Income
Net income	$ 149,925	$ 109,826	$ 423,930	$ 312,766
Other comprehensive income:
Unrealized (appreciation) depreciation on securities	(61,257)	(25,037)	32,851	133,424
Income taxes	23,185	9,389	(12,106)	(50,033)
Unrealized (appreciation) depreciation on securities, net of tax	(38,072)	(15,648)	20,745	83,391
Minimum pension liability adjustments	862	751	2,588	2,251
Income taxes	(306)	(282)	(953)	(845)
Minimum pension liability adjustments, net of tax	556	469	1,635	1,406
Total comprehensive income	112,409	94,647	446,310	397,563
Accumulated other comprehensive income, net of related income taxes
Unrealized appreciation on securities	146,871		146,871		126,126
Unrecognized actuarial loss and prior service cost	(25,583)		(25,583)		(27,218)
Accumulated other comprehensive income	$ 121,288		$ 121,288		$ 98,908