Commercial Mortgage Residual Interests (Schedule of Amounts Recognized as Unrealized Gains and/or Losses Recorded as Other Comprehensive Income and Other Than Temporary Valuation Impairments Recorded in Earnings) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Commercial Mortgage Residual Interests [Abstract]
Unrealized gains (losses), net	$ (182)	$ (585)	$ 875
Other than temporary valuation impairment	$ 6,830	$ 531	$ 256