Summary Of Significant Accounting Policies (Narrative) (Details) (USD $)			3 Months Ended
Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2011 Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Threshold amount of balance outstanding for secured loans receivable annually reviewed			$ 1,500,000
Related ACL	$ 3,498,000	$ 3,755,000

Minimum amount of loans which receive annual review if secured by property in one of the following categories: multi-family (five or more units) property, unimproved land, other improved commercial property, acquisition and development of land projects, developed building lots, office building, single-use building, or retail building.

No definition available.

Name:	cffn_AnnualReviewOfLoansReceivableSecuredByPropertyOutstandingAmount
Namespace Prefix:	cffn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration