Commercial Mortgage Residual Interests Commercial Mortgage Residual Interests (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended			12 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013 securitizations		Jun. 30, 2012	Dec. 31, 2012
Mortgage Loans on Real Estate [Line Items]
Number of securitizations			7
Discount rate			25.00%			25.00%
Loss severity of loans in foreclosure			20.00%			20.00%
LIBOR			Forward 3-month curve			Forward 3-month curve
Prime			Forward curve			Forward curve
Unrealized gains	$ 350	$ 213	$ 1,219		$ 213
Other than temporary valuation impairment	$ 0	$ 2,718	$ 0		$ 2,718
Maximum [Member]
Mortgage Loans on Real Estate [Line Items]
Average life equivalent CPR speeds range			23.71%	[1]		24.31%	[1]
Foreclosures frequency curve default model			4.07%			4.49%
Minimum [Member]
Mortgage Loans on Real Estate [Line Items]
Average life equivalent CPR speeds range			0.80%	[1]		0.08%	[1]
Foreclosures frequency curve default model			0.08%			0.09%

[1] Conditional prepayment rate.