Earnings Per Common Share - Narrative (Details) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Net Income
Basic earnings per share	$ 73,300	$ 85,519	$ 156,697	$ 158,350
Stock options	0	0	0	0
Restricted stock	0	0	0	0
Diluted earnings per share	$ 73,300	$ 85,519	$ 156,697	$ 158,350
Shares
Basic earnings per share (in shares)	64,238	65,733	64,175	65,631
Stock options (in shares)	227	388	267	399
Restricted stock (in shares)	566	468	586	311
Diluted earnings per share (in shares)	65,031	66,589	65,028	66,341
Per Share Amount
Basic earnings per share (in dollars per share)	$ 1.14	$ 1.30	$ 2.44	$ 2.41
Stock options (in dollars per share)	$ 0.00	$ (0.01)	$ (0.01)	$ (0.01)
Restricted stock (in dollars per share)	$ (0.01)	$ (0.01)	$ (0.02)	$ (0.01)
Diluted earnings per share (in dollars per share)	$ 1.13	$ 1.28	$ 2.41	$ 2.39
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding stock options, excluded in the calculation of earnings per share	252	289	252	289