Commercial Mortgage Residual Interests Commercial Mortgage Residual Interests (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended			12 Months Ended
	Sep. 30, 2013 securitizations	Sep. 30, 2012	Sep. 30, 2013 securitizations		Sep. 30, 2012	Dec. 31, 2012
Mortgage Loans on Real Estate [Line Items]
Number of securitizations			7
Discount rate						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
Number of securitizations, discount rate valuation adjustment at 20%	3		3
Number of securitization, discount rate valuation adjustment at 25%	4		4
Unrealized gains	$ 376	$ 0	$ 1,595		$ 213
Other than temporary valuation impairment	$ 16	$ 0	$ 16		$ 2,718
Maximum [Member]
Mortgage Loans on Real Estate [Line Items]
Discount rate			25.00%
Average life equivalent CPR speeds range			19.39%	[1]		24.31%	[1]
Foreclosures frequency curve default model			3.97%			4.49%
Minimum [Member]
Mortgage Loans on Real Estate [Line Items]
Discount rate			20.00%
Average life equivalent CPR speeds range			0.80%	[1]		0.80%	[1]
Foreclosures frequency curve default model			0.07%			0.09%

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