Investment Securities (Investment Securities Held at a Continuous Loss) (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Sep. 30, 2022
Schedule of Available For Sale Securities [Line Items]
Investments securities available-for-sale, continuous unrealized loss position, less than 12 Months	$ 216,204	$ 265,631
Investments securities available-for-sale, continuous unrealized loss position less than 12 Months, Accumulated Loss	10,316	17,702
Investments securities available-for-sale, continuous unrealized loss position, 12 months or longer	244,583	190,739
Investments securities available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	36,125	26,002
Investments securities available-for-sale, continuous unrealized loss position	460,787	456,370
Investments securities available-for-sale, continuous unrealized loss position, accumulated loss	46,441	43,704
REMIC's
Schedule of Available For Sale Securities [Line Items]
Investments securities available-for-sale, continuous unrealized loss position, less than 12 Months	215,958	261,795
Investments securities available-for-sale, continuous unrealized loss position less than 12 Months, Accumulated Loss	10,315	17,260
Investments securities available-for-sale, continuous unrealized loss position, 12 months or longer	240,933	190,739
Investments securities available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	35,722	26,002
Investments securities available-for-sale, continuous unrealized loss position	456,891	452,534
Investments securities available-for-sale, continuous unrealized loss position, accumulated loss	46,037	43,262
Fannie Mae Certificates
Schedule of Available For Sale Securities [Line Items]
Investments securities available-for-sale, continuous unrealized loss position, less than 12 Months	246	217
Investments securities available-for-sale, continuous unrealized loss position less than 12 Months, Accumulated Loss	1	4
Investments securities available-for-sale, continuous unrealized loss position, 12 months or longer	0	0
Investments securities available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	0	0
Investments securities available-for-sale, continuous unrealized loss position	246	217
Investments securities available-for-sale, continuous unrealized loss position, accumulated loss	1	4
U.S. government and agency obligations
Schedule of Available For Sale Securities [Line Items]
Investments securities available-for-sale, continuous unrealized loss position, less than 12 Months	0	3,619
Investments securities available-for-sale, continuous unrealized loss position less than 12 Months, Accumulated Loss	0	438
Investments securities available-for-sale, continuous unrealized loss position, 12 months or longer	3,650	0
Investments securities available-for-sale, continuous unrealized loss position, 12 months or longer, accumulated loss	403	0
Investments securities available-for-sale, continuous unrealized loss position	3,650	3,619
Investments securities available-for-sale, continuous unrealized loss position, accumulated loss	$ 403	$ 438

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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