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Commercial Mortgage Residual Interests (Narrative) (Details) | 12 Months Ended
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Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($) securitization | Dec. 31, 2015 USD ($) securitization
Commercial Mortgage Residual Interests [Abstract] |  |  |
Number of securitizations | securitization |  | 5 | 7
Other than temporary valuation impairment | $ | $ 0 | $ 6,830,000 | $ 531,000
Remaining number of securitizations | securitization |  | 2 |
Residuals at fair value | $ | $ 36,000 |  |

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- Definition Commercial Mortgage Residual Interests [Abstract] + References No definition available. + Details
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- Definition Number of Securitizations + References No definition available. + Details
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- Definition Remaining Number of Securitizations + References No definition available. + Details
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- Definition The charge against earnings to reduce the carrying value of an interest continued to be held by the transferor in a securitized financial instrument. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 325 -SubTopic 40 -Section 35 -Paragraph 4 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=82899219&loc=d3e44297-111616 + Details
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- Definition Fair value portion of interest continued to be held by a transferor after transferring financial assets to a third party. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 10 -Section 15 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=77996609&loc=d3e94415-111705 + Details
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