Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share
Net income	$ 18,187	$ 20,444	$ 18,898	$ 19,474	$ 4,276	$ 22,511	$ 57,529	$ 46,261
Income allocated to participating securities	(12)			(16)			(39)	(38)
Net income available to common stockholders	$ 18,175			$ 19,458			$ 57,490	$ 46,223
Total basic average common shares outstanding	135,504,869			138,018,052			135,450,951	137,961,231
Effect of dilutive stock options	32,283			0			26,615	31,747
Total diluted average common shares outstanding	135,537,152			138,018,052			135,477,566	137,992,978
Net EPS:
Basic	$ 0.13			$ 0.14			$ 0.42	$ 0.34
Diluted	$ 0.13			$ 0.14			$ 0.42	$ 0.34
Antidilutive stock options, excluded from the diluted average common shares outstanding calculation	93,565			813,645			210,529	405,522
Average Common Shares Outstanding [Member]
Earnings Per Share
Total basic average common shares outstanding	135,421,817			137,935,000			135,409,349	137,919,631
Average Committed ESOP Shares Outstanding [Member]
Earnings Per Share
Total basic average common shares outstanding	83,052			83,052			41,602	41,600