Selected Quarterly Financial Data (Unaudited) (Summary Of Quarterly Data) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Selected Quarterly Financial Information [Abstract]
Total interest and dividend income	$ 83,285	$ 82,211	$ 82,037	$ 82,421	$ 77,313	$ 82,161	$ 81,774	$ 80,644	$ 329,954	$ 321,892	$ 313,186
Net interest and dividend income	49,811	51,681	52,597	52,301	50,077	49,433	49,889	49,374	206,390	198,773	195,382
Provision for credit losses	300	450	0	0	0	0	0	0	750	0	0
Net income	$ 22,409	$ 22,897	$ 24,554	$ 24,383	$ 21,389	$ 22,372	$ 23,330	$ 31,836	$ 94,243	$ 98,927	$ 84,137
Basic EPS	$ 0.16	$ 0.17	$ 0.18	$ 0.18	$ 0.16	$ 0.17	$ 0.17	$ 0.24	$ 0.68	$ 0.73	$ 0.63
Diluted EPS	0.16	0.17	0.18	0.18	0.16	0.17	0.17	0.24	0.68	0.73	0.63
Dividends declared per share	$ 0.085	$ 0.335	$ 0.085	$ 0.475	$ 0.085	$ 0.335	$ 0.085	$ 0.375	$ 0.98	$ 0.88	$ 0.88
Average number of basic shares outstanding	137,801,000	137,720,000	137,635,000	137,551,000	135,500,000	134,484,000	134,428,000	134,373,000	137,676,923	134,698,344	134,082,420
Average number of diluted shares outstanding	137,867,000	137,788,000	137,691,000	137,592,000	135,556,000	134,530,000	134,475,000	134,467,000	137,735,401	134,758,991	134,243,862