Foreclosed Assets (Narrative) (Details) - property	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Multi-Family Mortgage Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Properties transferred into REO		1
Single-Family Mortgage Loans [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Number of Properties transferred into REO	0

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_FinancingReceivableRecordedInvestmentPastDueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration