Commercial Mortgage Residual Interests (Schedule of Key Assumptions Used in Determining the Value of the Residuals) (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Mortgage Loans On Real Estate [Line Items]
Discount rate		20.00%	20.00%
Loss severity of loans in foreclosure		20.00%	20.00%
LIBOR		Forward 3-month curve	Forward 3-month curve
Prime		Forward curve	Forward curve
Fair value at December 31		$ 36	$ 11,115
Minimum
Mortgage Loans On Real Estate [Line Items]
Average life equivalent CPR speeds range (percent)	[1]	0.87%	0.87%
Foreclosures frequency curve default model (percent)		0.00%	0.72%
Maximum
Mortgage Loans On Real Estate [Line Items]
Average life equivalent CPR speeds range (percent)	[1]	21.56%	21.73%
Foreclosures frequency curve default model (percent)		1.33%	1.57%

[1] Conditional prepayment rate