Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share
Net income	$ 20,210	$ 19,983	$ 19,688	$ 17,813	$ 16,067	$ 17,995	$ 17,715	$ 17,563	$ 77,694	$ 69,340	$ 74,513
Income allocated to participating securities									(176)	(205)	(69)
Net income available to common stockholders									$ 77,518	$ 69,135	$ 74,444
Total basic average common shares outstanding	137,047,000	138,332,000	139,489,000	142,882,000	142,856,000	143,263,000	145,382,000	147,883,000	139,440,073	144,847,156	157,912,978
Effect of dilutive stock options									1,891	853	3,422
Total diluted average common shares outstanding	137,051,000	138,334,000	139,489,000	142,883,000	142,858,000	143,263,000	145,382,000	147,883,000	139,441,964	144,848,009	157,916,400
Net EPS:
Basic	$ 0.15	$ 0.14	$ 0.14	$ 0.12	$ 0.11	$ 0.13	$ 0.12	$ 0.12	$ 0.56	$ 0.48	$ 0.47
Diluted	$ 0.15	$ 0.14	$ 0.14	$ 0.12	$ 0.11	$ 0.13	$ 0.12	$ 0.12	$ 0.56	$ 0.48	$ 0.47
Antidilutive stock options, excluded from the diluted average common shares outstanding calculation									2,060,748	2,430,629	1,308,925
Average Common Shares Outstanding [Member]
Earnings Per Share
Total basic average common shares outstanding									139,377,615	144,638,458	157,704,473
Average Committed ESOP Shares Outstanding [Member]
Earnings Per Share
Total basic average common shares outstanding									62,458	208,698	208,505