Allowance for Loan Losses (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Commercial [Member]
Financing Receivable, Impaired [Line Items]
Unpaid principal balance of impaired securitized loans	$ 0	$ 4,724
Basis adjustments related to impaired securitized loans	0	8
Amortized cost basis of impaired securitized loans	0	4,732
Interest income recognized on impaired securitized loans		109	609
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance at beginning of period	(2,268)	(4,200)	(3,935)
Provision for loan losses	24	848	1,194
Credit losses, net of recoveries	(2,142)	(2,780)	(929)
Allowance at end of period	(150)	(2,268)	(4,200)
Single-family [Member]
Financing Receivable, Impaired [Line Items]
Unpaid principal balance of impaired securitized loans	3,380	3,000
Basis adjustments related to impaired securitized loans	50	48
Amortized cost basis of impaired securitized loans	3,430	3,048
Interest income recognized on impaired securitized loans	179	162	205
Financing Receivable, Allowance for Credit Losses [Roll Forward]
Allowance at beginning of period	(231)	(270)	(277)
Provision for loan losses	168	23	0
Credit losses, net of recoveries	(110)	(62)	(7)
Allowance at end of period	$ (289)	$ (231)	$ (270)