Selected Quarterly Financial Data (Unaudited) (Summary Of Quarterly Data) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Selected Quarterly Financial Information [Abstract]
Total interest and dividend income	$ 71,606	$ 74,381	$ 78,955	$ 80,036	$ 83,285	$ 82,211	$ 82,037	$ 82,421	$ 304,978	$ 329,954	$ 321,892
Net interest and dividend income	45,683	46,287	48,668	48,697	49,811	51,681	52,597	52,301	189,335	206,390	198,773
Provision for credit losses	0	0	22,075	225	300	450	0	0	22,300	750	0
Net income	$ 18,279	$ 19,474	$ 4,276	$ 22,511	$ 22,409	$ 22,897	$ 24,554	$ 24,383	$ 64,540	$ 94,243	$ 98,927
Basic EPS	$ 0.13	$ 0.14	$ 0.03	$ 0.16	$ 0.16	$ 0.17	$ 0.18	$ 0.18	$ 0.47	$ 0.68	$ 0.73
Diluted EPS	0.13	0.14	0.03	0.16	0.16	0.17	0.18	0.18	0.47	0.68	0.73
Dividends declared per share	$ 0.085	$ 0.085	$ 0.085	$ 0.425	$ 0.085	$ 0.335	$ 0.085	$ 0.475	$ 0.68	$ 0.98	$ 0.88
Average number of basic shares outstanding	137,705,000	138,018,000	137,968,000	137,898,000	137,801,000	137,720,000	137,635,000	137,551,000	137,896,704	137,676,923	134,698,344
Average number of diluted shares outstanding	137,705,000	138,018,000	138,000,000	137,976,000	137,867,000	137,788,000	137,691,000	137,592,000	137,901,188	137,735,401	134,758,991