Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share
Net income	$ 19,474	$ 4,276	$ 22,511	$ 22,897	$ 24,554	$ 24,383	$ 46,261	$ 71,834
Income allocated to participating securities	(16)			(16)			(38)	(35)
Net income available to common stockholders	$ 19,458			$ 22,881			$ 46,223	$ 71,799
Total basic average common shares outstanding	138,018,052			137,720,480			137,961,231	137,635,099
Effect of dilutive stock options	0			67,048			31,747	55,335
Total diluted average common shares outstanding	138,018,052			137,787,528			137,992,978	137,690,434
Net EPS:
Basic	$ 0.14			$ 0.17			$ 0.34	$ 0.52
Diluted	$ 0.14			$ 0.17			$ 0.34	$ 0.52
Antidilutive stock options, excluded from the diluted average common shares outstanding calculation	813,645			457,486			405,522	491,669
Average Common Shares Outstanding [Member]
Earnings Per Share
Total basic average common shares outstanding	137,935,000			137,637,428			137,919,631	137,593,497
Average Committed ESOP Shares Outstanding [Member]
Earnings Per Share
Total basic average common shares outstanding	83,052			83,052			41,600	41,602