Financial Instruments and Fair Value Measurement (Details) (USD $)	3 Months Ended			9 Months Ended
	Jun. 30, 2013	Dec. 31, 2012 item	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Sep. 30, 2012
Available-for-sale securities
Number of limited partnerships that entity sold shares of the partnership		3
Earnings per diluted share (in dollars per share)	$ 2.46		$ 1.38	$ 5.33	$ 3.88
Limited Liability Partnerships
Realized gain from sale of investment securities		$ 8,800,000
Non-qualified Supplemental Savings Plan
Assets held in Non-qualified Supplement Savings Plan, at Fair Value	10,100,000			10,100,000		8,200,000
Available-for-sale securities
Available-for-sale securities
Realized gain on shares sold in an available-for-sale security	153,400,000
After-tax gain	92,449,000			92,449,000
Earnings per diluted share (in dollars per share)	$ 0.86			$ 0.86
Equity securities
Available-for-sale securities
Cost	68,434,000			68,434,000		129,183,000
Gross unrealized gains	209,097,000			209,097,000		304,396,000
Estimated fair value	$ 277,531,000			$ 277,531,000		$ 433,579,000