Loans Receivable And Allowance For Credit Losses (Classified Loans) (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Sep. 30, 2025
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	$ 640,990	$ 1,033,723
Year Two	954,820	560,108
Year Three	489,733	1,067,458
Year Four	877,469	1,215,877
Year Five	1,165,848	1,385,026
Prior Years	3,876,625	2,748,460
Revolving Line of Credit	127,716	117,327
Revolving Line of Credit Converted to Term Loan	7,603	8,021
Total Amortized Cost	8,140,804	8,136,000
One- to Four-Family Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	118,393	233,573
Year Two	227,503	233,389
Year Three	211,670	601,344
Year Four	565,970	972,071
Year Five	933,385	1,266,835
Prior Years	3,659,951	2,607,234
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	5,716,872	5,914,446
One- to Four-Family Segment [Member] \| Originated [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Amortized Cost	3,679,335	3,776,443
One- to Four-Family Segment [Member] \| Originated [Member] \| Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	118,393	233,573
Year Two	227,023	232,879
Year Three	210,407	296,339
Year Four	278,931	529,728
Year Five	508,747	739,138
Prior Years	2,312,503	1,722,587
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	3,656,004	3,754,244
One- to Four-Family Segment [Member] \| Originated [Member] \| Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	0
Year Two	480	0
Year Three	763	1,409
Year Four	1,501	1,099
Year Five	1,213	1,672
Prior Years	4,555	4,614
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	8,512	8,794
One- to Four-Family Segment [Member] \| Originated [Member] \| Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	363
Year Four	361	568
Year Five	299	469
Prior Years	14,159	12,005
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	14,819	13,405
One- to Four-Family Segment [Member] \| Correspondent Purchased [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Amortized Cost	1,927,514	2,023,397
One- to Four-Family Segment [Member] \| Correspondent Purchased [Member] \| Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	0
Year Two	0	510
Year Three	500	301,792
Year Four	282,798	439,538
Year Five	422,286	524,927
Prior Years	1,212,420	748,902
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	1,918,004	2,015,669
One- to Four-Family Segment [Member] \| Correspondent Purchased [Member] \| Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	1,441
Year Four	1,668	523
Year Five	0	366
Prior Years	722	367
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	2,390	2,697
One- to Four-Family Segment [Member] \| Correspondent Purchased [Member] \| Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	0
Year Four	711	615
Year Five	840	263
Prior Years	5,569	4,153
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	7,120	5,031
One- to Four-Family Segment [Member] \| Bulk Purchased [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Amortized Cost	110,023	114,606
One- to Four-Family Segment [Member] \| Bulk Purchased [Member] \| Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	0
Year Four	0	0
Year Five	0	0
Prior Years	106,343	110,862
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	106,343	110,862
One- to Four-Family Segment [Member] \| Bulk Purchased [Member] \| Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	0
Year Four	0	0
Year Five	0	0
Prior Years	1,596	1,564
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	1,596	1,564
One- to Four-Family Segment [Member] \| Bulk Purchased [Member] \| Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	0
Year Four	0	0
Year Five	0	0
Prior Years	2,084	2,180
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	2,084	2,180
Commercial Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	518,709	790,804
Year Two	719,945	319,284
Year Three	271,791	461,181
Year Four	307,332	239,182
Year Five	228,562	116,952
Prior Years	213,641	139,000
Revolving Line of Credit	49,776	41,536
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	2,309,756	2,107,939
Commercial Segment [Member] \| Commercial Real Estate [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Amortized Cost	2,077,923	1,898,183
Commercial Segment [Member] \| Commercial Real Estate [Member] \| Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	439,207	639,555
Year Two	624,768	292,900
Year Three	248,004	396,152
Year Four	280,838	208,604
Year Five	200,794	111,266
Prior Years	205,043	134,388
Revolving Line of Credit	11,144	9,775
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	2,009,798	1,792,640
Commercial Segment [Member] \| Commercial Real Estate [Member] \| Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	7,587
Year Two	6,847	0
Year Three	0	36,266
Year Four	0	16,060
Year Five	15,090	0
Prior Years	0	80
Revolving Line of Credit	415	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	22,352	59,993
Commercial Segment [Member] \| Commercial Real Estate [Member] \| Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	40,386	39,962
Year Two	0	142
Year Three	297	2,681
Year Four	2,631	0
Year Five	160	106
Prior Years	2,101	2,609
Revolving Line of Credit	198	50
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	45,773	45,550
Commercial Segment [Member] \| Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Amortized Cost	231,833	209,756
Commercial Segment [Member] \| Commercial and Industrial [Member] \| Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	38,932	103,700
Year Two	88,088	25,950
Year Three	23,359	26,082
Year Four	23,840	14,387
Year Five	12,409	5,555
Prior Years	6,497	1,923
Revolving Line of Credit	36,930	31,287
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	230,055	208,884
Commercial Segment [Member] \| Commercial and Industrial [Member] \| Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	114	0
Year Two	0	0
Year Three	0	0
Year Four	0	44
Year Five	30	0
Prior Years	0	0
Revolving Line of Credit	220	355
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	364	399
Commercial Segment [Member] \| Commercial and Industrial [Member] \| Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	70	0
Year Two	242	292
Year Three	131	0
Year Four	23	87
Year Five	79	25
Prior Years	0	0
Revolving Line of Credit	869	69
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	1,414	473
Consumer Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	3,888	9,346
Year Two	7,372	7,435
Year Three	6,272	4,933
Year Four	4,167	4,624
Year Five	3,901	1,239
Prior Years	3,033	2,226
Revolving Line of Credit	77,940	75,791
Revolving Line of Credit Converted to Term Loan	7,603	8,021
Total Amortized Cost	114,176	113,615
Consumer Segment [Member] \| Home Equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Amortized Cost	106,849	105,179
Consumer Segment [Member] \| Home Equity [Member] \| Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	2,347	5,609
Year Two	4,961	5,532
Year Three	4,891	3,513
Year Four	3,196	3,755
Year Five	3,233	1,064
Prior Years	2,921	2,166
Revolving Line of Credit	77,486	75,067
Revolving Line of Credit Converted to Term Loan	7,490	7,937
Total Amortized Cost	106,525	104,643
Consumer Segment [Member] \| Home Equity [Member] \| Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	0
Year Two	0	0
Year Three	0	33
Year Four	13	0
Year Five	0	0
Prior Years	0	0
Revolving Line of Credit	64	251
Revolving Line of Credit Converted to Term Loan	79	42
Total Amortized Cost	156	326
Consumer Segment [Member] \| Home Equity [Member] \| Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	100
Year Two	98	0
Year Three	0	0
Year Four	0	0
Year Five	0	0
Prior Years	4	11
Revolving Line of Credit	32	57
Revolving Line of Credit Converted to Term Loan	34	42
Total Amortized Cost	168	210
Consumer Segment [Member] \| Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Total Amortized Cost	7,327	8,436
Consumer Segment [Member] \| Other [Member] \| Pass [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	1,538	3,629
Year Two	2,311	1,877
Year Three	1,359	1,354
Year Four	958	824
Year Five	641	175
Prior Years	107	49
Revolving Line of Credit	358	416
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	7,272	8,324
Consumer Segment [Member] \| Other [Member] \| Special Mention [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	0
Year Two	0	0
Year Three	10	0
Year Four	0	0
Year Five	0	0
Prior Years	0	0
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	10	0
Consumer Segment [Member] \| Other [Member] \| Substandard [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	3	8
Year Two	2	26
Year Three	12	33
Year Four	0	45
Year Five	27	0
Prior Years	1	0
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Amortized Cost	$ 45	$ 112

Capitol Federal Financial, Inc. 10-Q