Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share
Net income	$ 22,511	$ 24,383
Income allocated to participating securities	(19)	(9)
Net income available to common stockholders	$ 22,492	$ 24,374
Total basic average common shares outstanding	137,898,010	137,550,920
Effect of dilutive stock options	78,112	41,459
Total diluted average common shares outstanding	137,976,122	137,592,379
Net EPS:
Basic	$ 0.16	$ 0.18
Diluted	$ 0.16	$ 0.18
Antidilutive stock options, excluded from the diluted average common shares outstanding calculation	435,750	550,021
Average Common Shares Outstanding [Member]
Earnings Per Share
Total basic average common shares outstanding	137,897,561	137,550,471
Average Committed ESOP Shares Outstanding [Member]
Earnings Per Share
Total basic average common shares outstanding	449	449