Loans Receivable and Allowance for Credit Losses (Gross Charge-offs) (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	$ 8	$ 5
Year Two	6	12
Year Three	77	0
Year Four	0	0
Year Five	7	0
Prior Years	25	0
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Charge-offs	123	17
One- to Four-Family Segment [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	0	0
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Charge-offs	0	0
One- to Four-Family Segment [Member] \| Originated [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	0	0
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Charge-offs	0	0
One- to Four-Family Segment [Member] \| Correspondent Purchased [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	0	0
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Charge-offs	0	0
One- to Four-Family Segment [Member] \| Bulk Purchased [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	0	0
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Charge-offs	0	0
Commercial Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	0
Year Two	0	0
Year Three	77	0
Year Four	0	0
Year Five	0	0
Prior Years	25	0
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Charge-offs	102	0
Commercial Segment [Member] \| Commercial Real Estate [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	0	0
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Charge-offs	0	0
Commercial Segment [Member] \| Commercial and Industrial [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	0
Year Two	0	0
Year Three	77	0
Year Four	0	0
Year Five	0	0
Prior Years	25	0
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Charge-offs	102	0
Consumer Segment [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	8	5
Year Two	6	12
Year Three	0	0
Year Four	0	0
Year Five	7	0
Prior Years	0	0
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Charge-offs	21	17
Consumer Segment [Member] \| Home Equity [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	8	5
Year Two	6	11
Year Three	0	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 Charge-offs	14	16
Consumer Segment [Member] \| Other [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Year One	0	0
Year Two	0	1
Year Three	0	0
Year Four	0	0
Year Five	7	0
Prior Years	0	0
Revolving Line of Credit	0	0
Revolving Line of Credit Converted to Term Loan	0	0
Total Charge-offs	$ 7	$ 1

Capitol Federal Financial, Inc. 10-Q