Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Earnings Per Share
Net income	$ 21,527	$ 19,234	$ 42,245	$ 39,706
Income allocated to participating securities	(16)	(27)	(43)	(69)
Net income available to common stockholders	$ 21,511	$ 19,207	$ 42,202	$ 39,637
Total basic average common shares outstanding	132,960,030	136,208,029	132,890,781	136,147,295
Effect of dilutive stock options	71,012	37,756	80,473	32,327
Total diluted average common shares outstanding	133,031,042	136,245,785	132,971,254	136,179,622
Net EPS:
Basic	$ 0.16	$ 0.14	$ 0.32	$ 0.29
Diluted	$ 0.16	$ 0.14	$ 0.32	$ 0.29
Antidilutive stock options, excluded from the diluted average common shares outstanding calculation	921,199	863,827	898,386	920,365
Average Common Shares Outstanding [Member]
Earnings Per Share
Total basic average common shares outstanding	132,918,277	136,166,271	132,869,793	136,126,419
Average Committed ESOP Shares Outstanding [Member]
Earnings Per Share
Total basic average common shares outstanding	41,753	41,758	20,988	20,876