Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share
Net income	$ 19,688	$ 17,715	$ 37,501	$ 35,278
Income allocated to participating securities	(44)	(51)	(94)	(111)
Net income available to common stockholders	$ 19,644	$ 17,664	$ 37,407	$ 35,167
Total basic average common shares outstanding	139,489,033	145,381,605	141,204,147	146,645,899
Total diluted average common shares outstanding	139,489,324	145,381,718	141,204,751	146,646,006
Net earnings per share:
Basic	$ 0.14	$ 0.12	$ 0.26	$ 0.24
Diluted	$ 0.14	$ 0.12	$ 0.26	$ 0.24
Antidilutive stock options, excluded from the diluted average common shares outstanding calculation	2,060,216	2,463,165	2,396,610	2,466,339
Average Common Shares Outstanding [Member]
Earnings Per Share
Total basic average common shares outstanding	139,447,275	145,242,074	141,183,271	146,576,142
Average Committed ESOP Shares Outstanding [Member]
Earnings Per Share
Total basic average common shares outstanding	41,758	139,531	20,876	69,757
Effect Of Dilutive Stock Options [Member]
Earnings Per Share
Total diluted average common shares outstanding	291	113	604	107