Earnings Per Common Share - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net Income
Basic earnings per share	$ 112,992	$ 71,925	$ 281,879	$ 228,622
Stock options	0	0	0	0
Restricted stock and performance units	0	0	0	0
Diluted earnings per share	$ 112,992	$ 71,925	$ 281,879	$ 228,622
Shares
Basic earnings per share (in shares)	64,649,000	64,309,000	64,557,000	64,204,000
Stock options (in shares)	61,000	216,000	74,000	250,000
Restricted stock (in shares)	420,000	535,000	432,000	569,000
Diluted earnings per share (in shares)	65,130,000	65,060,000	65,063,000	65,023,000
Per Share Amount
Basic earnings per share (in dollars per share)	$ 1.75	$ 1.12	$ 4.37	$ 3.56
Stock options (in dollars per share)	0.00	0.00	0.00	(0.01)
Restricted stock (in dollars per share)	(0.02)	(0.01)	(0.04)	(0.02)
Diluted earnings per share (in dollars per share)	$ 1.73	$ 1.11	$ 4.33	$ 3.52
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Outstanding stock options, excluded in the calculation of earnings per share	873,000	0	867,000	0